CN111133494B

CN111133494B - Sea chart image display device

Info

Publication number: CN111133494B
Application number: CN201780094427.4A
Authority: CN
Inventors: 樋口和树
Original assignee: Honda Electronics Co Ltd
Current assignee: Honda Electronics Co Ltd
Priority date: 2017-09-01
Filing date: 2017-09-01
Publication date: 2022-04-05
Anticipated expiration: 2037-09-01
Also published as: JP6911230B2; JPWO2019043931A1; CN111133494A; WO2019043931A1

Abstract

For each mesh obtained by dividing a chart image by the number of pixels smaller than the number of pixels of a chart screen of the chart image, the depth of water at the bottom of the water measured for the mesh is assigned (S1), and smoothing is performed on the depth of water assigned to the bottom of the water of each mesh (S2). The depth of water at the bottom of the water allocated to the mesh after the smoothing process is expanded, and the depth of water at the bottom of the water for each pixel of the chart image is allocated (S3). Using the water depth of the water bottom, an image showing the water depth of the water bottom at each position is displayed on the chart screen.

Description

Sea chart image display device

Technical Field

The present invention relates to a chart image display device mounted on a ship and displaying a chart image showing a state in water measured at each position on a chart on a display unit.

Background

Conventionally, a fish finder device has been known (for example, patent document 1) which is mounted on a ship, and has a plotter function of displaying a map image (a marine image) of an ocean, a lake, a river, a pond, or the like around the ship on a display device and showing a track, which is a track of a route through which the ship passes, on the marine image. In this fish finder, there are the following devices: based on the depth from the water surface to the water bottom (track data) at each point measured while the ship is underway, the depth from the water surface to the water bottom at each position of the ocean or the like is expressed by color on the chart image, or the depth from the water surface to the water bottom at each position of the ocean or the like is expressed by an isobath. With such a fish finder, the user can grasp the topography of the water bottom and guide the ship to a place where the topography may exist while viewing the course of the ship.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 3047028

Non-patent document

Non-patent document 1: an "iso-red ear," a "method of drawing a high-altitude profile" (a method of drawing an iso-contour), [ online ], 6/month and 2/2002, a "green-month house," a "search 5/8/2017", and the internet < URL: http:// hp.vector.co.jp/authors/VA019223/Tips/Alg _02.html >.

Disclosure of Invention

Problems to be solved by the invention

In order to more accurately represent the topography of the water bottom on a chart image, a chart image is generated based on a large amount of track data. However, when interpolation processing is performed using a large amount of track data, a huge amount of calculation is required.

For example, conventionally, as a method for drawing a deep line such as a deep line on a chart image, the following method is known (for example, non-patent document 1): every time all the track data is searched, 3 adjacent points are selected, a virtual plane of a triangle having the 3 adjacent points as vertexes is generated by interpolation processing, and an isobath passing through the virtual plane is obtained. Here, when the neighboring 3 points are selected from the 10000-point track data, it is necessary to perform the calculation of the distance between the two points and the comparison calculation by the order of 10000.

As described above, in order to more accurately represent the topography of the water bottom on the marine map image, a CPU having high computation capability is required in the conventional technology.

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a chart image display device capable of accurately representing a state in water on a chart image with a small amount of computation.

Means for solving the problems

To achieve the object, a chart image display device according to claim 1 is mounted on a ship and displays a chart image showing a state in water obtained by measurement at each position on a chart on a display unit, the chart image display device including: an acquisition unit that acquires position information of a ship; a vibrator capable of transmitting ultrasonic waves into water and receiving reflected waves of the ultrasonic waves; a measurement unit that drives the transducer to transmit ultrasonic waves and measures the state of the ship in water around the ship's position based on a reception signal obtained by receiving a reflected wave of the ultrasonic waves by the transducer; a storage unit that stores information indicating the state in the water measured by the measurement unit so as to correspond to the position of the ship acquired by the acquisition unit; an assigning unit that divides the chart image displayed on the display unit into a plurality of meshes, and assigns information indicating the state in the water measured at a position corresponding to each mesh, from the information stored in the storage unit; a smoothing unit that performs smoothing processing on each of the meshes based on the information indicating the state in water distributed to the mesh by the distribution unit and the information indicating the state in water distributed to the neighboring meshes by the distribution unit; and an image generating unit that generates a chart image to be displayed on the display unit based on information showing the state in water of each mesh smoothed by the smoothing unit.

The chart image display device according to claim 2 is the chart image display device according to claim 1, wherein the assigning unit assigns information showing the state in the water to the meshes divided by the number of pixels smaller than the number of pixels of the chart image displayed on the display unit.

The chart image display device according to claim 3 is the chart image display device according to claim 2, further comprising an expansion processing unit that performs expansion processing on information showing a state in water of each mesh smoothed by the smoothing processing unit to calculate information showing the state in water for each pixel of the chart image,

the image generating unit generates a chart image to be displayed on the display unit based on the information indicating the state in the water of each of the pixels calculated by the expansion processing unit.

The chart image display device according to claim 4 is the chart image display device according to claim 3, wherein the expansion process is an expansion process based on bilinear interpolation.

The chart image display device according to claim 5 is the chart image display device according to any one of claims 1 to 4, wherein the smoothing unit performs smoothing processing on each mesh using only the mesh to which information indicating the state in the water has been assigned.

The chart image display device according to claim 6 is the chart image display device according to any one of claims 1 to 5, wherein the assignment unit assigns information indicating the state in the water that is most recently measured in terms of time to one grid, when a plurality of pieces of information indicating the state in the water measured at a position corresponding to the one grid are present in the storage unit.

The chart image display device according to claim 7 is the chart image display device according to claim 6, wherein the assigning unit assigns, to each mesh, information showing the state in the water measured at a position corresponding to the mesh in order to cover the information showing the state in the water measured earlier in time from the information showing the state in the water stored in the storage unit.

The chart image display device according to claim 8 is the chart image display device according to any one of claims 1 to 7, including: a color specification unit that classifies the information indicating the state in the water measured by the measurement unit for each predetermined range, and specifies a different color for each range; a color specifying information assigning unit that assigns information for specifying the color specified by the color specifying unit to the state in water measured at each position included in the chart image displayed on the display unit, based on the information showing the state in water of each mesh smoothed by the smoothing unit; a second image generating unit that generates an image showing the state in the water measured at each position, using the color specified by the information assigned by the color specifying information assigning unit; a color tone change position detection unit that detects a change position of a color tone of the color in the image generated by the second image generation unit; and a replacement unit configured to replace the change position detected by the color tone change position detection unit with a specific color with respect to the image generated by the second image generation unit, wherein the image generation unit generates a chart image to be displayed on the display unit based on the image in which the change position has been replaced with the specific color by the replacement unit.

A chart image display device according to claim 9 is mounted on a ship, and displays a chart image showing a state in water obtained by measurement at each position on a chart on a display unit, the chart image display device including: an acquisition unit that acquires position information of a ship; a vibrator capable of transmitting ultrasonic waves into water and receiving reflected waves of the ultrasonic waves; a measurement unit that drives the transducer to transmit ultrasonic waves and measures the state of the ship in water around the ship's position based on a reception signal obtained by receiving a reflected wave of the ultrasonic waves by the transducer; a storage unit that stores information indicating the state in the water measured by the measurement unit so as to correspond to the position information of the ship acquired by the acquisition unit; a color specification unit that classifies the information indicating the state in the water measured by the measurement unit for each predetermined range, and specifies a different color for each range; a color specifying information assigning unit that assigns information for specifying the color specified by the color specifying unit to the state in the water measured at each position included in the chart image displayed on the display unit, based on the information stored in the storage unit; a second image generating unit that generates an image showing the state in the water measured at each position, using the color specified by the information assigned by the color specifying information assigning unit; a color tone change position detection unit that detects a change position of a color tone of the color in the image generated by the second image generation unit; a replacement unit configured to replace the change position detected by the color tone change position detection unit for the image generated by the second image generation unit with a specific color; and a display control unit that generates the chart image based on the image in which the change position has been changed to a specific color by the changing unit, and displays the chart image on the display unit.

The chart image display device according to claim 10 is the chart image display device according to claim 8 or 9, wherein the color tone change position detection unit performs a spatial differentiation process using information for specifying the color assigned by the color specifying information assignment unit to each position included in the chart image displayed on the display unit, and detects a pixel having a differential value whose absolute value is larger than a predetermined value as the change position of the color tone of the color.

The chart image display device according to claim 11 is the chart image display device according to any one of claims 8 to 10, including:

a color information storage unit that stores information for specifying a color specified by the color specification unit for each predetermined range so as to correspond to the range;

a range width specifying unit configured to specify that a width of the predetermined range specified as a different color by the color specifying unit is 1/n of a width of the one predetermined range, where n is a natural number of 2 or more; and

a calculation unit that multiplies n by information showing the state in the water at each position when the range width specification unit specifies that the width of the predetermined range is 1/n of the width of the one predetermined range,

wherein, when the range width specification unit specifies that the width of the predetermined range is 1/n of the width of the one predetermined range, the color specification information assignment unit assigns information for specifying the color specified by the color specification unit to the state in the water measured at each position included in the chart image displayed on the display unit, based on the information showing the state in the water multiplied by n by the calculation unit.

The chart image display device according to claim 12 is the chart image display device according to any one of claims 1 to 11, wherein the underwater state is a depth from a water surface to a water bottom.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the chart image display device described in claim 1, the ultrasonic wave is transmitted from the transducer, and the reflected wave of the ultrasonic wave is received by the transducer. The underwater state in the vicinity of the position of the ship is measured by the measurement unit based on the reception signal obtained by receiving the reflected wave. Information indicating the state in the water obtained by the measurement is stored in the storage unit so as to correspond to the position information of the ship acquired by the position information acquisition unit. On the other hand, the chart image displayed on the display unit is divided into a plurality of meshes, and the distribution unit distributes, to each mesh, information showing the state in water measured at a position corresponding to the mesh, from among the information stored in the storage unit. Then, for each mesh, the smoothing unit performs smoothing processing based on the information showing the state in water distributed to the mesh by the distribution unit and the information showing the state in water distributed to the neighboring mesh by the distribution unit. The image generating unit generates a chart image based on the information showing the state in water of each mesh smoothed by the smoothing unit, and displays the chart image on the display unit. In this way, the amount of computation required to generate the chart image depends on the number of meshes, because the chart image is divided into meshes, information indicating the measured state in water is assigned to each mesh, and the chart image is generated after smoothing is performed on each mesh. Therefore, the following effects are obtained: even when there is a large amount of information showing the measured state in water, the state in water can be accurately represented on the chart image with a small amount of computation.

According to the chart image display device of claim 2, the following effects are obtained in addition to the effects obtained by the chart image display device of claim 1. That is, the information showing the state in water is assigned by the assigning unit to the mesh divided by the number smaller than the number of pixels of the chart image displayed on the display unit. This has the effect of enabling the underwater state to be represented on the chart image with a smaller amount of computation and with higher accuracy than in the case where the chart image is divided into meshes by the same number as the number of pixels of the chart image, for example.

According to the chart image display device of claim 3, the following effects are obtained in addition to the effects obtained by the chart image display device of claim 2. That is, the information showing the state in water of each mesh subjected to the smoothing processing by the smoothing processing unit is subjected to the expansion processing by the expansion processing unit, and the information showing the state in water is calculated for each pixel of the marine map image. The image generating unit generates a chart image to be displayed on the display unit based on the information indicating the state in water of each pixel calculated by the expansion processing unit. This has the following effects: even if the information showing the underwater state is assigned by the assigning unit to the mesh divided by the number smaller than the number of pixels of the chart image displayed on the display unit, the underwater state can be accurately represented on the chart image.

According to the chart image display device of claim 4, the following effects are obtained in addition to the effects obtained by the chart image display device of claim 3. That is, the information showing the state in water of each mesh subjected to the smoothing processing by the smoothing processing unit is subjected to the extension processing by bilinear interpolation, and the information showing the state in water is calculated for each pixel of the marine image. This has the following effects: even if the information showing the underwater state is distributed by the distribution unit to the meshes divided by the number smaller than the number of pixels of the chart image displayed on the display unit, the underwater state can be accurately represented on the chart image with a small amount of computation.

According to the chart image display device of claim 5, the following effects are obtained in addition to the effects obtained by the chart image display device of any one of claims 1 to 4. That is, the smoothing unit smoothes each mesh using only the mesh to which information indicating the state in water has been assigned. This has the following effects: since it is possible to suppress smoothing processing using a mesh in which information indicating the state in water does not exist effectively, the state in water can be represented on the chart image more accurately.

According to the chart image display device of claim 6, the following effects are obtained in addition to the effects obtained by the chart image display device of any one of claims 1 to 5. That is, when a plurality of pieces of information showing the state in water measured at a position corresponding to one grid exist in the storage unit, the assignment unit assigns, to the one grid, information showing the state in water that is measured most recently in time. This has the following effects: the latest measurement result can be reflected on the state in water shown on the chart image.

According to the chart image display device of claim 7, the following effects are obtained in addition to the effects obtained by the chart image display device of claim 6. That is, the distribution unit distributes, in order to be overlaid, information showing the state in water measured at a position corresponding to the mesh, from information showing the state in water measured earlier in time among the information showing the state in water stored in the storage unit. This has the following effects: even if the information showing the state in water newly measured in time out of the information showing the state in water measured at the position corresponding to one grid is not searched out from the storage unit, the information showing the state in water newly measured in time out of the information showing the state in water measured at the position corresponding to the one grid can be easily assigned.

According to the chart image display device of claim 8, the following effects are obtained in addition to the effects obtained by the chart image display device of any one of claims 1 to 7. That is, the color specification unit classifies the information indicating the state in water measured by the measurement unit for each predetermined range, and specifies different colors for each range. The color specifying information assigning unit assigns information for specifying the color specified by the color specifying unit to the state in water measured at each position included in the chart image displayed on the display unit, based on the information showing the state in water of each mesh smoothed by the smoothing unit. The second image generating unit generates an image showing the state of the water measured at each position, using the color specified by the information assigned by the color specifying information assigning unit. The color tone change position detection unit detects a change position of the color tone of the color in the image generated by the second image generation unit. Here, the changing position detected by the color tone changing position detecting unit with respect to the image generated by the second image generating unit is replaced with a specific color by the replacing unit. The image generating unit generates a chart image to be displayed on the display unit based on the image in which the changing position has been changed to the specific color by the changing unit. Thus, the state in water displayed on the chart image is displayed in a specific color at a division of a predetermined range displayed in different colors. The lines connected by the specific color are contour lines formed by connecting points in the same state in water within the width of each predetermined range. In this way, the position of the contour line is detected only by determining the color tone change position of the color displayed in a different color within each predetermined range. Therefore, the underwater state can be accurately represented on the chart image with a small amount of computation.

According to the chart image display apparatus of claim 9, the ultrasonic wave is transmitted from the transducer, and the reflected wave of the ultrasonic wave is received by the transducer. The underwater state in the vicinity of the position of the ship is measured by the measurement unit based on the reception signal obtained by receiving the reflected wave. Information indicating the state in the water obtained by the measurement is stored in the storage unit so as to correspond to the position information of the ship acquired by the position information acquisition unit. On the other hand, the color specification unit classifies the information indicating the state in water measured by the measurement unit for each predetermined range, and specifies different colors for each range. The color specifying information assigning unit assigns information for specifying the color specified by the color specifying unit to the state in water measured at each position included in the chart image displayed on the display unit, based on the information stored in the storage unit. The second image generating unit generates an image showing the state of the water measured at each position, using the color specified by the information assigned by the color specifying information assigning unit. The color tone change position detection unit detects a change position of the color tone of the color in the image generated by the second image generation unit. Here, the changing position detected by the color tone changing position detecting section with respect to the image generated by the second image generating section is replaced with a specific color by the replacing section. The display control unit generates a chart image based on the image whose change position has been changed to a specific color by the changing unit, and displays the chart image on the display unit. Thus, the state in water displayed on the chart image is displayed in a specific color at a division of a predetermined range displayed in different colors. The lines connected by the specific color are contour lines formed by connecting points in the same state in water within the width of each predetermined range. In this way, the position of the contour line is detected only by determining the color tone change position of the color displayed in a different color within each predetermined range. Therefore, the underwater state can be accurately represented on the chart image with a small amount of computation.

According to the chart image display device of the invention 10, the following effects are obtained in addition to the effects obtained by the chart image display device of the invention 8 or 9. That is, the color tone change position detection unit performs spatial differentiation processing using information for specifying the color assigned by the color specifying information assignment unit to each position included in the chart image displayed on the display unit, and detects a pixel whose absolute value of the differential value is larger than a predetermined value as the change position of the color tone of the color. This has the effect that the position of the contour can be determined with a smaller amount of computation.

According to the chart image display device of claim 11, the following effects are obtained in addition to the effects obtained by the chart image display device of any one of claims 8 to 10. That is, the color information storage unit stores information for specifying the color specified by the color specification unit for each predetermined range so as to correspond to the range. When the range width specification unit specifies that the width of a predetermined range in which different colors are specified by the color specification unit is 1/n (n is a natural number of 2 or more) of the width of one predetermined range, the arithmetic unit multiplies the information indicating the state in water at each position by n. Then, the color specifying information assigning unit assigns information for specifying the color specified by the color specifying unit to the state in water measured at each position included in the chart image displayed on the display unit, based on the information showing the state in water multiplied by n by the arithmetic unit. This has the following effects: by storing information for specifying the color specified by the color specifying unit in the range in advance so as to correspond to each of the predetermined ranges, the width of the predetermined range in which the color specifying unit specifies a different color can be easily set to 1/n of the width of the predetermined range. In this case, the arithmetic unit multiplies the information indicating the state in water at each position of the chart image by n. Thus, compared to the case where the width of the predetermined range in which the different color is specified by the color specification unit is actually 1/n (divided), there is an effect that the width of the predetermined range in which the different color is specified by the color specification unit can be substantially 1/n of the width of one predetermined range by an operation (multiplication) with a small operation amount.

According to the chart image display device according to claim 12, in addition to the effects of the chart image display device according to any one of claims 1 to 11, the following effects are obtained: since the state in water shown in the chart image is the depth from the water surface to the water bottom, the depth from the water surface to the water bottom can be accurately represented in the chart image with a small amount of computation.

Drawings

Fig. 1 is a schematic diagram schematically showing a configuration of a fish school detection device as an embodiment of a chart image display device according to the present invention.

Fig. 2 is a schematic diagram showing, from the side of the ship, a state in which the fish finder device performs detection of the water bottom right under the ship and acquires position information of the ship.

Fig. 3 is a block diagram showing an electrical configuration of the fish finder.

Fig. 4 is a schematic diagram schematically showing an example of a water depth color mapping table stored in the flash memory.

Fig. 5 is a diagram showing a relationship between pixels of a chart image displayed on a display device and a grid set in the chart image.

Fig. 6 is a flowchart showing a chart image generation process executed by the CPU.

Fig. 7 (a) is a diagram showing an image in which the depth of water in water allocated to each position included in the chart image is indicated by a corresponding display color, and (b) is a diagram showing an image in which an iso-depth line is added to the image shown in (a).

Detailed Description

Hereinafter, a mode for carrying out the present invention will be described with reference to the accompanying drawings. First, an outline of the fish school detection device 12 as an embodiment of the nautical chart image display device according to the present invention will be described with reference to fig. 1 and 2. Fig. 1 is a schematic diagram schematically showing the structure of the fish finder 12. Fig. 2 is a schematic diagram showing, from the side of the ship 11, a state in which the fish finder 12 finds the bottom of the water directly below the ship 11 and acquires position information of the ship 11.

The fish finder 12 is mounted on the ship 11, detects a detection target object such as a fish in water directly under the ship 11 by transmission and reception of ultrasonic waves, and displays a detection image on the display device 15. The fish finder 12 switches the display mode to the chart display mode to display a chart image of the ocean, lake, river, pond, etc. around the ship 11 on the display 15. Fig. 1 shows a state where the chart image is displayed on the display device 15.

The fish finder 12 is configured to measure the depth (depth) d of water from the water surface to the water bottom by transmission and reception of the ultrasonic beam TB. The fish finder 12 is configured to show the depth d of the water bottom at each position by a color and an isobath on the chart image displayed on the display device 15 based on the depth d of the water bottom at each position in the ocean or the like measured by the fish finder 12 while the ship 11 is underway.

The detailed structure of the fish finder 12 will be described. The fish finder 12 is constituted by: a main body 13; an operation button 14 provided on the main body 13 and receiving an input from a user; a display device 15 integrally formed with the main body 13; a transducer 16 that transmits and receives an ultrasonic beam TB; and a GPS antenna 17 for receiving a signal transmitted from a GPS satellite S as an artificial satellite for a global positioning system.

The vibrator 16 is fixed to the vessel 11 and electrically connected to the main body 13 by a cable. The transducer 16 is driven based on a signal transmitted from the main body 13, and transmits (irradiates) an ultrasonic beam TB in one direction (for example, directly below the ship 11). The transducer 16 receives a reflected wave of the ultrasonic beam TB reflected from the object to be detected or the bottom of the sea, the lake bottom, the river bottom, the pond bottom, or the like, and transmits a received signal obtained by the reception to the main body 13.

The GPS antenna 17 is fixed to the vessel 11 and electrically connected to the main body 13 by a cable. The signals transmitted from the plurality of GPS satellites S are received by the GPS antenna 17, and the received signals are transmitted to the main body 13.

The main body 13 of the fish finder 12 is disposed in a steering room of the ship 11, for example. When receiving a reception signal obtained by receiving a reflected wave of the ultrasonic beam TB by the transducer 16, the main body 13 generates a probe image based on the reception signal, and displays the probe image on the display device 15.

The main body 13 calculates the water depth d of the water bottom based on the time from the transmission of the ultrasonic beam TB until the reception of the reflected wave, receives the reception signals from the plurality of GPS satellites S from the GPS antenna 17, and acquires the position (latitude and longitude) of the ship (own ship) 11 based on the reception signals. Then, when the main body 13 calculates the water depth d of the water bottom, the positional information of the ship 11 at this time is associated with the calculated water depth d of the water bottom, and is sequentially stored as track data 22b (see fig. 3). Here, the track data 22b is stored in the flash memory 22 in the order of the depth d of the water bottom measured (i.e., in the order from the track data 22b measured earlier in time).

When the display mode is the chart display mode, the main body 13 displays the chart image around the ship 11 on the display device 15, and based on the track data 22b, the depth d of the water at each position of the chart image is shown by a color and an equal depth line on the chart image displayed on the display device 15.

Next, an electrical configuration of the fish finder 12 will be described with reference to fig. 3. Fig. 3 is a block diagram showing an electrical configuration of the fish finder 12. The fish finder 12 has a control device 20 inside the main body 13. The control device 20 controls the operation of the fish finder 12, and includes a Central processing Unit (cpu) 21, a flash Memory 22, a Random Access Memory (RAM) 23, a transmission/reception circuit 31, a display controller 32, a Video RAM (Video RAM) 33, and a GPS interface circuit (hereinafter, referred to as "GPS I/F") 34.

The CPU 21 is connected to the flash memory 22, the RAM 23, the transmission/reception circuit 31, the display controller 32, and the GPS I/F34, and further connected to the operation buttons 14 (see fig. 1) from the outside of the control device 20. The transducer 16 (see fig. 1) is connected to the transmission/reception circuit 31. The VRAM 33 and the display device 15 (see fig. 1) are connected to the display controller 32. The GPS antenna 17 (see fig. 1) is connected to the GPS I/F34.

The CPU 21 is an arithmetic device that executes various arithmetic operations for controlling the operation of the fish finder 12 in accordance with the program data 22a stored in the flash memory 22.

The flash memory 22 is a rewritable nonvolatile memory for storing fixed value data and the like in addition to the program data 22 a. The program data and a part of the fixed value data may be stored not in the flash memory 22 but in a nonvolatile memory (for example, a mask ROM) provided separately from the flash memory 22 and not to be rewritten.

The flash memory 22 stores at least the chart data 22c and the water depth color conversion table 22d in addition to the track data 22 b. The chart data 22c is data for displaying a chart of the ocean, lake, river, pond, etc. in the area where the fish school determination device 12 is supposed to be used on the display device 15. When the display mode of the fish finder 12 is the chart display mode, the CPU 21 reads chart data 22c around the position of the ship 11 determined based on the reception signal of the GPS satellite S from the flash memory 22. Then, based on the read chart data 22c, a chart around the ship 11 is displayed on the display device 15.

The water depth color conversion table 22d is a table for assigning the display color at each position on the chart according to the water depth d at the water bottom when the water depth d of the water bottom at the position is expressed in color on the chart displayed on the display device 15 in the chart display mode. Here, details of the water depth color conversion table 22d will be described with reference to fig. 4. Fig. 4 is a schematic diagram schematically showing an example of the water depth color conversion table 22 d.

As shown in fig. 4, the water depth color conversion table 22d is prepared as an index 22d1 expressing the color of the water depth d of the water bottom by "0" - "99", and defines a color palette of the color (display color) displayed by the index 22d1 by the luminance of each of red (R)22d2, green (G)22d3, and blue (B)22d4 in correspondence with each index 22d 1. That is, the water depth color conversion table 22d divides the water depth d of the water bottom into 100 indexes 22d1, and specifies different display colors in a form corresponding to each index 22d 1. That is, the value Id of the index 22d1 is information for determining a display color to be displayed for the water depth d of the water bottom, and is composed of 8 bits. In addition, the number of indexes 22d1 for dividing the water depth d of the water bottom does not need to be 100, and may be any number.

For example, the depth d of the water bottom is associated with each index 22d1 in the depth-color conversion table 22d as follows. That is, the water depth d of the water bottom is divided by the width of 8m, and the water depth d of the water bottom is associated with each index 22d1 by the following expression (1) so that a different display color 22d2 is specified for each range.

Here, Id is the value of index 22d1 corresponding to the water depth d [ m ] at the water bottom. The value obtained on the right side of the expression (1) is rounded off to a decimal point or less. When the depth d of water at the bottom is 800m or more, Id is set to 99.

In the fish finder 12, the depth d of the water bottom is assigned the value Id of the corresponding index 22d1 by equation (1), and the display color (color determined by the brightness of each color RGB) corresponding to the value Id in the depth-color conversion table 22d is set as the display color indicating the depth d of the water bottom.

In the water depth color conversion table 22d, the color of the isobath to be displayed is defined for the index 22d1 being "255" in association with the display of the water depth d of the water bottom on the chart image by color. The index 22d1 "255" is associated with a specific color (black here) as a display color. Therefore, when the depth d of the water bottom is displayed in color on the chart image, a contour line is displayed in a specific color (black). The specific color is preferably a color different from the display color assigned to the water depth d at the water bottom (the display color determined by the indices 22d1 "0" - "99").

The water depth color conversion table 22d does not correspond to the display colors (RGB) of "100" to "254" in the index 22d1, and is not used.

The description is continued with reference to fig. 3. The RAM 23 is a rewritable volatile memory and temporarily stores various data when the CPU 21 executes a program. The RAM 23 stores at least mesh data 23 a.

The mesh data 23a is data obtained by associating each of a plurality of meshes 42 set in the chart image displayed on the display device 15 with a value of the water depth d of the water bottom measured at a position included in the mesh 42.

Here, the mesh 42 set for the chart image will be described with reference to fig. 5. Fig. 5 is a diagram showing a relationship between pixels 41 of a chart image displayed on the display device 15 and a grid 42 set in the chart image. The chart image is constituted by pixels of 1280 dots in the horizontal direction × 1280 dots in the vertical direction, for example, in accordance with the resolution of the display device 15. One grid 42 is set for each set of 8 horizontal pixels 41 × 8 vertical pixels. Each grid 42 is set so that pixels included in the grid do not overlap with each other. In addition, all the pixels 41 are included in an arbitrary grid 42. Thus, a grid 42 of 160 dots in the horizontal direction × 160 dots in the vertical direction is set for the chart image.

When the chart image is displayed on the display device 15, the CPU 21 reads the track data 22b from the flash memory 22 in the order from the old to the new. Then, it is determined whether or not the track data 22b is data showing the water depth d of the water bottom measured at the point included in the chart image displayed on the display device 15, based on the position information included in the read track data 22 b. When it is determined that the track data 22b is data showing the water depth d of the water bottom measured at the point included in the chart image, the water depth d of the water bottom included in the track data 22b is stored as the mesh data 23a in association with the mesh 42 corresponding to the measurement point. The grid data 23a is used to assign a water depth d of the water bottom at a position on the chart corresponding to each grid 42.

Here, when the depth d of the water bottom is measured, the ultrasonic beam TB used for the measurement has a fixed pointing angle θ (see fig. 2), and therefore the detection range of the water bottom (beam radius r of the ultrasonic wave) also has a predetermined width. That is, the measured water depth d of the water bottom does not indicate the water depth d of the water bottom at an accurate position, but can be referred to as the water depth d of the water bottom within a range having a predetermined width. Therefore, even if the depth d of the water bottom to be measured is assigned to the grid 42 having a fixed width, the accuracy of the topography of the water bottom shown in the chart image is not affected.

When it is determined that one piece of track data 22b is data showing the water depth d of the water bottom measured at the point included in the chart image, if the water depth d of the water bottom has already been associated with the grid 42 corresponding to the measurement point, the water depth d of the water bottom included in the one piece of track data 22b is overwritten in an overlaying manner. As described above, the track data 22b is stored in the flash memory 22 in the order of the measurement of the water depth d of the water bottom from old to new in time, and when the chart image is displayed on the display device 15, the track data 22b is read from the flash memory 22 in the order of the measurement of the water depth d of the water bottom from old to new.

This allocates the water depth d of the water bottom that is measured most recently in time to the grid 42. Therefore, the depth d of the water bottom reflecting the latest measurement result can be shown on the chart image displayed on the display device 15. Further, even if the water depth d of the water bottom measured at the position included in one grid 42 is not searched for from the track data 22b, the water depth d of the water bottom measured at the position included in the one grid 42 can be easily assigned to the one grid 42.

The description is continued with reference to fig. 3. The transmission and reception circuit 31 is a circuit for driving the transducer 16 based on control from the CPU 21 to transmit the ultrasonic beam TB from the transducer 16 and also receiving input of a reception signal obtained by receiving a reflected wave of the transmitted ultrasonic beam TB by the transducer 16. The transmitting and receiving circuit 31 digitizes the reception signal inputted from the transducer 16 and stores the digitized reception signal as reception signal data in the RAM 23 connected to the CPU 21.

The display controller 32 is a controller that controls display on the display device 15 based on control from the CPU 21. The VRAM 33 is a memory provided with a frame buffer for storing one frame of image such as a chart image to be displayed on the display device 15.

When receiving an instruction to draw an image to be displayed on the display device 15, the display controller 32 draws an image having an instruction at a position instructed by the CPU 21 to the frame buffer of the VRAM 33 using the chart data 22c stored in the flash memory 22 and image data not shown. Then, the display controller 32 reads the image drawn in the frame buffer and displays the image on the display device 15.

The GPS I/F34 is a device that inputs signals from GPS satellites S received by the GPS antenna 17 to the CPU 21.

Next, details of the chart image generation process executed by the CPU 21 will be described with reference to fig. 6 and 7. The chart image generation processing is processing for generating a chart image to be displayed on the display device 15, and is executed by the CPU 21 every predetermined time when the display mode is set to the chart display mode. Fig. 6 is a flowchart showing the chart image generation processing. Fig. 7 is a diagram showing an image generated in the middle of execution of the chart image generation process. Specifically, (a) of fig. 7 shows the depth d of water in water allocated to each position included in the chart image in the corresponding display color, and (b) of fig. 7 shows the image shown in (a) of fig. 7 with the isobath added thereto.

In the chart image generation process, as shown in fig. 6, first, a mesh registration process is executed (S1). In the mesh registration processing, each of a plurality of meshes 42 (see fig. 5) set in the chart image displayed on the display device 15 is associated with a value of the water depth d of the water bottom measured at a position included in the mesh 42 based on the course data 22b and stored as mesh data 23 a.

Specifically, as described above, the track data 22b is read from the flash memory 22 in the order of the water depths d at the bottom of the water being measured, and when it is determined that the read track data 22b is data showing the water depths d at the bottom of the water measured at the points included in the chart image, the water depths d at the bottom of the water included in the track data 22b are stored as the grid data 23a so as to be overlappingly associated with the grid 42 including the measurement points.

In the chart image generation process, an inter-mesh smoothing process is next performed (S2). In the inter-grid smoothing processing, for each grid 42 set for the chart image, smoothing is performed by applying a spatial filter based on the water depth d of the water bottom allocated to the grid 42 by the processing of S1 and the water depth d of the water bottom allocated to 8 grids 42 existing around the grid 42 by the processing of S1. Specifically, the spatial filter is applied by the following equation, where xy is the coordinate in the space where the grid 42 is set, uv is the coordinate of the filter coefficient, Dxy is the water depth d of the water bottom at the grid 42 after the application of the spatial filter, Dxy is the water depth d of the water bottom at the grid 42 before the application of the spatial filter and the grid 42 existing in the periphery of the grid 42, Cuv is the spatial filter coefficient, Axy is the coefficient indicating whether or not the water depth Dxy of the water bottom effective by distributing the water depth d of the water bottom to the grid 42 at the coordinate xy by the processing of S1.

[ mathematical formula 1]

At the stage of the processing of S1, the time (time) for measurement may be greatly different between the water depth d of the water bottom allocated to one grid 42 and the water depth d of the water bottom allocated to the grid 42 in the vicinity thereof. When the measurement time is different, an error occurs in the depth d of the water bottom due to the rise and fall of the water surface, the change of the topography of the water bottom, and the like. Further, the calculation of the water depth d at the bottom of the water by the transmission and reception of the ultrasonic beam TB also generates a measurement error. Therefore, the water depth d of the water bottom allocated to each grid 42 may be different from the actual water depth of the water bottom by more than a certain amount. In contrast, by performing the inter-grid smoothing process of S2, the variation in the water depth d at the bottom of the water between the grids 42 can be suppressed.

In addition, by applying the spatial filter of the above equation 1, it is possible to perform operations 160 × 160=25600 times as the number of meshes 42 and perform the inter-mesh smoothing processing with a small amount of operations. In particular, in the present embodiment, a spatial filter is applied to the number of grids 42 smaller than the number of pixels of the chart image. For example, in the example shown in fig. 5, the number of pixels of the chart image is 1280 × 1280 dots, and the grid 42 is 160 × 160 dots. Thus, compared to the case where the depth d of the water bottom is assigned to each pixel of the marine image and the spatial filter is applied, smoothing processing can be performed with an amount of calculation of 1/8 × 1/8= 1/64.

In the present embodiment, the spatial filter is applied using only the grid 42 having the depth d of water where the effective water bottom exists, using the above equation 1. This can suppress smoothing of the grid 42 including the water depth d in which the water bottom does not effectively exist, and thus can accurately represent the water depth d of the water bottom on the chart image.

In the chart image generation process, the expansion process is next performed (S3). In this expansion processing, the grid 42 of 160 × 160 points to which the water depth d of the water bottom is assigned after the inter-grid smoothing processing of S2 is expanded to each pixel of 1280 × 1280 points which is the same as the number of pixels of the chart image, and the water depth d of the water bottom is assigned to each pixel. As a method of the extension processing, various kinds of processing are known, but for example, bilinear interpolation can be applied. The amount of computation required for the bilinear interpolation can be reduced compared to the amount of computation required for the smoothing process using the spatial filter in S2, and the resolution of the distribution of the water depth d at the bottom of the water can be made to match the resolution of the marine image. Therefore, the depth d of the water bottom can be smoothly expressed on the chart image.

In the chart image generation process, the color specific information assignment process is executed next (S4). In this color specifying information assignment process, the value Id of the index 22d1 corresponding to the water depth d of the water bottom assigned to each pixel obtained by the extension process of S3 is assigned to each pixel based on the water depth color conversion table 22 d. As described above, the value Id of the index 22d1 is information for determining the display color corresponding to the water depth d at the water bottom. The image shown in fig. 7 (a) is an image obtained by assigning, to each pixel, the value Id of the index 22d1 for specifying the display color corresponding to the water depth d of the water bottom at the pixel by the color specific information assignment process. As shown in fig. 7 (a), since different display colors are assigned according to the water depth d of the water bottom, it is possible for the user to easily grasp the topography of the water bottom at each position included in the chart image by the display colors.

In the chart image generation process, a spatial differentiation process is next performed (S5). In this spatial differentiation, spatial differentiation is performed for all of the values Id of the index 22d1 that have been assigned for determining a display color by the process of S4. Specifically, when Id (x, y) is a value Id of the index 22d1 assigned to a sample of coordinates (x, y), the sample of the coordinates (x, y) is spatially differentiated by the following expression (2), and a differential value a (x, y) is calculated.

In the chart image generation process, the iso-deepline rendering process is executed next (S6). In the deep line drawing process, it is determined whether or not the absolute value of the differential value a (x, y) calculated for each sample by the spatial differentiation process of S5 is equal to or greater than a predetermined value (for example, 1), and if the absolute value is equal to or greater than the predetermined value, the value Id of the index 22d1 for specifying the display color of the sample is set to "255" instead of being assigned by the color specifying information assignment process of S4. Thereby, the display color of the sample is set to a specific color (black) which is the display color of the isobath.

Here, the sample in which the absolute value of the differential value a (x, y) is equal to or greater than the predetermined value is a point at which the hue of the display color determined by the information assigned in the color specifying information assignment process of S4 changes. Thus, for example, the image shown in fig. 7 (a) (the image to which different display colors are assigned according to the water depth d of the water bottom) generated by the processing at S4 is a line 51 in which a specific color (black) is drawn at a place where the color tone of the display color changes, as shown in fig. 7 (b).

On the other hand, according to the water depth color conversion table 22d shown in fig. 4, the hue (hue) of the display color changes every time the water depth d at the bottom of the water changes by 8 m. Thus, the line 51 of the specific color drawn at the place where the hue of the display color is changed as shown in fig. 7 (b) becomes an equal-depth line per 8 m. Therefore, the iso-deep line can be drawn by the processing of S6.

Here, the amount of calculation required for the processing at S5 is the number of pixels × 5 times according to the above expression (2). This amount of calculation is only required because the value Id of the index 22d1 made of 8 bits for specifying the display color is spatially differentiated, not the display color (RGB data) itself. As described above, first, the value Id of the index 22d1 for specifying the display color that changes for each width (8 m in the present embodiment) over a predetermined range is assigned to the water depth d assigned to the water bottom of each pixel, spatial differentiation is performed using the assigned value Id of the index 22d1, and pixels corresponding to the change points of the color tone of the display color that can be determined as a result of the spatial differentiation are displayed with a specific color, whereby the contour line showing the water depth d of the water bottom can be shown on the marine map image with a small amount of computation. In the water depth color conversion table 22d, even between colors having similar hues of the corresponding display colors, the value Id of the index 22d1 is assigned with a difference of 1 or more for each display color. Therefore, even when the change in the color tone of the display color is small, the point of the change in the color tone can be reliably determined by performing the spatial differentiation process using the value Id of the index 22d 1.

After the generation of the chart image, the chart-seafloor topography image synthesis process is executed (S7), and the chart image generation process is terminated. In the chart and seafloor topography image synthesis process, first, the seafloor topography image in which each pixel is represented by a display color (specific color) corresponding to the value Id is generated by the processes of S4 and S6, based on information to which the value Id of the index 22d1 for determining the display color showing the water depth d of the water bottom at each position and the value Id (255) of the index 22d1 for determining the specific color showing the isobath have been assigned. Then, the submarine topography image is synthesized with the corresponding chart image. The sea chart image obtained by synthesizing the sea floor topography image is displayed on the display device 15.

As described above, the fish finder 12 performs the chart image generation process by the CPU 21, thereby providing the following effects. That is, with respect to each grid 42 set for the nautical chart image, the depth d of the water bottom is assigned to the grid 42, the depth d of the water bottom assigned to each grid 42 is smoothed, and an image showing the depth d of the water bottom at each position is displayed on the nautical chart screen using the depth d of the water bottom after the smoothing, so even when there are a plurality of track data 22b, the depth d of the water bottom can be displayed on the nautical chart screen with a small amount of computation and with high accuracy.

Further, since the depth d of the water bottom is assigned to the grid 42 divided by the number smaller than the number of pixels of the chart image and the smoothing process is performed, the depth d of the water bottom can be accurately displayed on the chart image with a smaller amount of computation than in the case where the depth d of the water bottom is assigned to each pixel of the chart image and the smoothing process is performed.

Further, by assigning the water depth d of the water bottom for each pixel of the marine image by the extension processing from the water depth d of the water bottom assigned to each mesh 42 after the smoothing processing, the resolution of assigning the water depth d of the water bottom can be matched with the resolution of the marine image. Therefore, the depth d of the water bottom can be smoothly expressed on the chart image. Further, by performing the extension processing by bilinear interpolation with a smaller amount of computation than the smoothing processing, the resolution at which the water depth d of the water bottom is distributed can be made to match the resolution of the chart image with a smaller amount of computation. Therefore, even if the water depth d of the water bottom is allocated to the grid 42 divided by the number smaller than the number of pixels of the chart image, the water depth d of the water bottom can be accurately represented on the chart image with a small amount of calculation.

In addition, the above-described effects can be achieved by the respective processes included in the chart image generation process.

The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments at all, and it can be easily estimated that various modifications and variations can be made without departing from the gist of the present invention. For example, the above-described embodiment described below may be configured by the modifications described below, or may be configured by a combination of these modifications. In addition, the numerical values, the filters, and the display colors corresponding to the depth lines such as the depth d · of the water bottom, which are listed in the above embodiments, are just examples, and it is needless to say that other numerical values, filters, and display colors may be adopted.

In the above-described embodiment, in the mesh registration processing (S1) of the chart image generation processing, the case where the depth d of the water bottom included in the track data 22b is associated with the mesh 42 including the measurement point when it is determined that the track data 22b read from the flash memory 22 is data showing the depth d of the water bottom measured at the point included in the chart image has been described.

On the other hand, as described above, the ultrasonic beam TB used for measuring the water depth d of the water bottom has a predetermined width, and the measured water depth d of the water bottom can be referred to as the water depth d of the water bottom within a range having the predetermined width. Further, a case is also assumed where the prescribed width is out of the range shown by one grid 42. In particular, when the depth d of water at the bottom of the water is large (the depth of water is deep), the predetermined width becomes larger.

Therefore, in the mesh registration processing (S1), when it is determined that the track data 22b read from the flash memory 22 is data showing the water depth d of the water bottom measured at the point included in the chart image, the water depth d of the water bottom included in the track data 22b may be associated with the mesh 42 including the measurement point and the mesh 42 existing in the periphery thereof. Thus, the depth d of the water bottom measured can be associated with the grid 42 according to the detection range of the ultrasonic beam TB, and therefore the depth d of the water bottom can be displayed more accurately on the chart screen.

In this case, the range of the grid 42 to which the water depth d of the water bottom is allocated may be changed. For example, the range of the grid 42 that distributes the water depth d at the bottom may be changed according to the place (sea area) where the ship 11 is located. For example, in the case of a location having a deep water bottom where the ship 11 is located, the depth of the water bottom can be associated with the grid 42 so that the detected depth d of the ultrasonic beam TB is more accurately reflected by increasing the range and in the case of a location having a flat and shallow water bottom where the ship 11 is located, by reducing the range.

The range of the grid 42 to which the water depth d of the water bottom is assigned may be changed according to the scale of the chart image displayed on the display device 15. For example, by increasing the range when the scale of the chart image is large and decreasing the range when the scale of the chart image is small, the depth d of the water bottom to be measured can be associated with the grid 42 so as to more accurately reflect the detection range of the ultrasonic beam TB.

Further, the range of the grid 42 to which the water depth d of the water bottom is allocated may be set by the user operating the operation button 14. This allows the user to freely adjust the range according to the intention of the user, and thus the depth d of the water bottom can be displayed on the chart image more accurately.

In the above embodiment, the following case is explained in the water depth color conversion table 22 d: in the color specifying information assigning process (S4) of the nautical chart image generating process, the different display colors at intervals of 8m are assigned to the water depths d assigned to the water bottom of each pixel based on the water depth color conversion table 22 d. In contrast, the interval of the water depths d of the water bottom to which different display colors are assigned may be changed according to user settings, a scale of the chart image, a setting of the fish finding depth when the fish finding image is displayed together with the chart image on the display device 15, and the like. This makes it possible to display the depth d of the water bottom on the chart image more accurately.

In this case, the water depth color conversion table 22d may be prepared for each interval of the water depths d of the water bottom to which different display colors are assigned. On the other hand, the interval of the water depths d of the water bottom to which different display colors are assigned in the color specifying information assigning process (S4) may be made variable while using one water depth color lut 22 d. For example, the interval of the water depths d of the water bottom to which different display colors are assigned by the single water depth color conversion table 22d may be set so that the interval of the water depths d of the water bottom to which different display colors are assigned in the color specifying information assignment process (S4) is 1/n (n is a natural number of 2 or more). The value of n may be determined according to user settings, a scale of the chart image, a setting of the fish finding depth when the fish finding image is displayed together with the chart image on the display device 15, and the like. Thus, even when the interval of the water depths d of the water bottom to which different display colors are assigned can be changed, it is not necessary to store a large number of water depth color look-up tables 22d in the flash memory 22, and therefore the storage capacity required by the flash memory 22 can be suppressed.

In this case, the depth d of the water bottom assigned to each pixel may be multiplied by n, and the display color may be assigned using one depth color conversion table 22d based on the depth (d × n) of the water bottom multiplied by n. Thus, the interval of the water depths d at the bottom of the water to which different display colors are assigned can be substantially set to 1/n by an operation (multiplication) with a smaller amount of operation than the case of multiplying the water depths d at the bottom of the water by 1/n.

In the above-described embodiment, the case where the specific color of the line 51 to be the iso-dark line is set to, for example, black in the iso-dark line drawing process (S6) of the chart image generation process has been described, but it is not always necessary to set one color, and a plurality of colors may be set as the specific color of the line 51. For example, black may be set as the color of the line 51 when the display color indicating the water depth d of the water bottom assigned to the pixels around the inlet line 51 is bright, and white may be set as the color of the line 51 when the display color indicating the water depth d of the water bottom assigned to the pixels around the inlet line 51 is dark. This makes it possible to make the line 51 that becomes an isobath conspicuous. The specific color of the line 51 is preferably a color other than a display color defined as a display color corresponding to the depth d of water at the bottom of the water.

In the above embodiment, the case where the depth d of the water bottom is measured by the ultrasonic beam TB and the depth d of the water bottom is indicated by a color or an isocontour line on the chart screen has been described, but the present invention is not limited to this. For example, the present invention can be applied to a case where the elements measured by the ultrasonic beam TB and shown by colors and contours on a chart screen are tidal currents, water temperatures, and bottom materials of the water bed.

In the above embodiment, the fish finder 12 is exemplified as the chart image display device, but the present invention is not limited thereto. For example, the present invention can also be applied to a plotter device that displays a chart and displays a track as a track on which the ship 11 travels. The present invention is also applicable to a sonar-type fish finder or plotter device that performs underwater and underwater detection over a predetermined range while changing the transmission direction of an ultrasonic beam TB transmitted in one direction.

Description of the reference numerals

11: a vessel; 12: a fish school detection device (chart image display device); 15: a display device (display unit); 16: a vibrator; 17: a GPS antenna (acquisition unit); 21: a CPU (part of the measurement unit); 22 b: track data (storage unit); 22 d: a water depth color conversion table (color specification unit, color information storage unit); 31: a transmission/reception circuit (part of the measurement section); 42: a grid; s1: (a distributing section); s2: (smoothing unit); s3: (expansion processing unit); s4: (color specifying information assigning unit, second image generating unit); s5; (spatial differentiation processing); s6: (replacement section); s7: (image generation unit, display control unit); TB: an ultrasound beam.

Claims

1. A marine map image display device that is mounted on a ship and displays a marine map image showing a state in water obtained by measurement at each position on a marine map on a display unit, the marine map image display device comprising:

an acquisition unit that acquires position information of a ship;

a vibrator capable of transmitting ultrasonic waves into water and receiving reflected waves of the ultrasonic waves;

a measurement unit that drives the transducer to transmit ultrasonic waves and measures the state of the ship in water around the ship's position based on a reception signal obtained by receiving a reflected wave of the ultrasonic waves by the transducer;

a storage unit that stores information indicating the state in the water measured by the measurement unit so as to correspond to the position information of the ship acquired by the acquisition unit;

an assigning unit that divides the chart image displayed on the display unit into a plurality of meshes in a number smaller than the number of pixels of the chart image, and assigns information indicating the state in the water measured at a position corresponding to each mesh from the information stored in the storage unit;

a smoothing unit that performs smoothing processing on each of the meshes based on the information indicating the state in water distributed to the mesh by the distribution unit and the information indicating the state in water distributed to the neighboring meshes by the distribution unit;

a color specification unit that classifies the information indicating the state in the water measured by the measurement unit for each predetermined range, and specifies a different color for each range;

a color specifying information assigning unit that assigns information for specifying the color specified by the color specifying unit to the state in water assigned to each pixel in the image corresponding to each mesh, based on the information showing the state in water of each mesh smoothed by the smoothing unit;

an image generating unit that generates an image showing the state in the water measured at each position, using the color specified by the information assigned by the color specifying information assigning unit;

a color tone change position detection unit that detects a change position of a color tone of the color in the image generated by the image generation unit, based on the information assigned by the color specific information assignment unit;

a replacement unit configured to replace the change position detected by the color tone change position detection unit for the image generated by the image generation unit with a specific color; and

and a display control unit that generates the chart image based on the image in which the change position has been changed to a specific color by the changing unit, and displays the chart image on the display unit.

2. The chart image display apparatus according to claim 1,

the smoothing unit performs smoothing processing on each mesh using only the mesh to which information indicating the state in the water has been assigned, and can perform smoothing processing while suppressing the mesh including information indicating that the state in the water does not exist effectively.

3. The chart image display apparatus according to claim 2,

when a plurality of pieces of information showing the state in the water measured at a position corresponding to one grid exist in the storage unit, the assignment unit assigns, to the one grid, information showing the state in the water newly measured in terms of time.

4. The chart image display apparatus according to claim 3,

the distribution unit distributes, in order from the information showing the state in water that is measured earlier in time among the information showing the state in water stored in the storage unit, information showing the state in water that is measured at a position corresponding to the mesh to each mesh in an overlaid manner.

5. A chart image display device which is mounted on a ship and displays a chart image showing a state in water measured at each position on a chart on a display unit, the chart image display device comprising:

an acquisition unit that acquires position information of a ship;

a color specifying information assigning unit that assigns information for specifying the color specified by the color specifying unit to the state in the water measured at each position included in the chart image displayed on the display unit, based on the information stored in the storage unit;

a color tone change position detection section that detects a change position of a color tone of the color in the image generated by the image generation section based on the information assigned by the color specific information assignment section;

6. The chart image display device according to any one of claims 1 to 5,

the color tone change position detection unit performs spatial differentiation processing on all of the values Id assigned to the index for specifying the display color by the processing performed by the color specifying information assignment unit, and detects a pixel whose differential value has an absolute value greater than a predetermined value as a change position of the color tone of the color.

7. The chart image display device according to any one of claims 1 to 5, comprising:

8. The chart image display device according to any one of claims 1 to 5,

the state in the water is the depth from the surface to the bottom.