TWI672482B - Indoor navigation system - Google Patents

Abstract

An indoor navigation system capable of capturing a spatial image feature point existing in an image of a previous scene through an analysis electronic device, and designing a spatial position of the indoor space to accurately locate an indoor location of the electronic device, and further according to the indoor location a space map of the space and a target location to be set, and a navigation route from the current location to the target location is planned, and displayed in the augmented reality mode in the front scene image currently displayed by the electronic device to guide the navigation The navigation icon of the route, and can accurately guide the user to walk in the indoor space by augmented real-time navigation, is an innovative indoor navigation technology.

Description

Indoor navigation system

The present invention relates to a navigation system, and more particularly to an indoor navigation system.

The common outdoor navigation is mainly through satellite positioning system. By analyzing the pre-established map map and satellite positioning data, navigation of specific locations can be performed. Since the satellite signal is blocked by the building, it is not suitable for indoor space navigation.

The traditional indoor navigation mainly arranges a plurality of communication nodes in the indoor space, and analyzes the strength of the communication signal between the electronic device and the communication node, so that the electronic device locates its position in the space, and The current location is indicated in a spatial plane map of the display, and the navigation icon is displayed on the space plane to facilitate the user to view, and the display content of the spatial plane map is changed as the current location changes. The purpose of navigation. However, this way of positioning and navigation through the spatial plane map, in addition to the large positioning error, is still easy to go wrong for those who do not look at the map or the concept of space is poor.

Although some operators have tried to use the Augmented Reality (AR) technology to directly overlay the navigation indicators in the scene images captured by the user's electronic device, thereby improving the navigation problem of the traditional space plane map. However, the positioning of such an AR navigation is performed by the communication signal between the electronic device and the positioning nodes, and there is still a problem of large positioning error.

Accordingly, it is an object of the present invention to provide an indoor navigation system that improves at least one of the disadvantages of the prior art.

Therefore, the indoor navigation system of the present invention is suitable for implementation in an electronic device, so that the electronic device can be used for navigation of an indoor space. The indoor navigation system comprises an image control unit, a navigation start unit, a spatial positioning unit, and a navigation planning control unit. The image control unit can drive the electronic device to capture and display a front scene image, and can display a navigation icon in an augmented reality manner in the front scene image. The navigation activation unit can be configured to set at least one target location to issue a navigation request. The spatial positioning unit stores a spatial map corresponding to the indoor space, and a plurality of spatial models respectively corresponding to the plurality of spatial positions in the spatial map, each spatial model having a plurality of spatial image feature points, and the spatial positioning unit The navigation request is triggered by the navigation activation unit, and the spatial image feature points of the front scene image currently displayed by the electronic device are analyzed according to the spatial image feature points of the spatial model to locate the electronic device. The current location is obtained by obtaining a current location, and the spatial location unit can also compare the spatial location corresponding to the at least one target location. The navigation planning control unit stores a plurality of navigation icons, and a navigation route from the current location to the spatial location corresponding to the at least one target location is planned according to the spatial map, and a navigation route is compared to guide the navigation route. The navigation icon corresponding to the direction of travel in the front scene image corresponding to the current position, and driving the image control unit to superimpose and display the compared navigation icon on the front scene image.

The effect of the invention is that the indoor navigation system can analyze the spatial image feature points in the front scene image captured by the electronic device for positioning, and can accurately locate the indoor location of the electronic device and accurately plan The navigation route is provided, and the user can accurately guide the user to walk in the indoor space by displaying the navigation icon in real time on the augmented reality instant navigation mode of the front scene image, which is an innovative indoor navigation technology.

The invention will be further illustrated by the following examples, but it should be understood that this embodiment is for illustrative purposes only and is not to be construed as limiting The number is indicated.

Referring to Figures 1, 2 and 3, an embodiment of the indoor navigation system 3 of the present invention is adapted to be implemented by an electronic circuit and/or a software program in an electronic device 800 that can be used by the user 600 to move through the electronic device. The device 800 performs spatial positioning and indoor navigation in an indoor space 700 of a building. The electronic device 800 has, for example but is not limited to, a mobile phone, a tablet computer, smart glasses or a smart watch. The electronic device 800 has a display 801, a lens 803 and a speaker 802.

The indoor navigation system 3 has a location map corresponding to the spatial locations of the indoor space 700, and a spatial map of all the walkway data connected between the spatial locations, and includes an image control unit 31 and a voice control. The unit 32, a navigation starting unit 33, a spatial positioning unit 34, a navigation planning control unit 36, a walkway recognizing unit 35, a moving speed judging unit 37, an obstacle recognizing unit 38, and a model correcting unit 39.

The image control unit 31 can control the electronic device 800 to capture the scene image in front of the lens 803 to obtain a front scene image 310, and drive the electronic device 800 to display the front scene image 310 on the display 801. The Augmented Reality (AR) technology controls the electronic device 800 to superimpose and display a navigation icon 360 transmitted by the navigation planning control unit 36 on the front scene image 310 displayed by the display 801. Since the augmented reality technology is numerous and not the improvement focus of the present invention, it will not be described in detail.

The voice control unit 32 can control the electronic device 800 to output a navigation voice transmitted by the navigation planning control unit 36 via the speaker 802 for the user 600 of the electronic device 800 to listen.

The navigation activation unit 33 can be operated to issue a positioning request, and when the operation is issued to send the positioning request, the image control unit 31 is driven to control the electronic device 800 to capture and display the front scene image 310, and touch the spatial positioning. The unit 34 performs positioning of the indoor space 700 based on the front scene image 310.

The navigation starting unit 33 stores a plurality of location options respectively corresponding to a plurality of spatial locations of the indoor space 700, and can be operated to set a location option as a target location to establish and issue a navigation request, and can be used in one Set multiple target locations in the navigation request. Each location option is set to identify the location and floor information of the respective spatial location in the spatial map, but the content of the location option is not limited thereto.

In addition, the navigation starting unit 33 also has an automatic planning mode and a manual planning mode that can be selectively activated when the navigation request is established. The navigation initiation unit 33 directly transmits the navigation request to the navigation planning control unit 36 when the automatic planning mode is selected to be activated to drive the navigation planning control unit 36 to plan the navigation route for the navigation request. When the manual planning mode is selected to be activated, the navigation starting unit 33 can operate to arrange the order of the target locations in the navigation request to set an arrival order, and transmit the navigation request with the arrival order set. The navigation planning control unit 36 is provided for the navigation planning control unit 36 to plan the navigation route for the navigation request. When the navigation activation unit 33 transmits the navigation request, the image control unit 31 synchronously drives the electronic device 800 to continuously capture and display the front scene image 310, and triggers the spatial positioning unit 34 to start according to the front scene image 310. The positioning of the indoor space 700 is performed.

The spatial location unit 34 has the spatial map built in, and a plurality of spatial models corresponding to the spatial locations. Each spatial model has a plurality of spatial image feature points for identifying corresponding spatial locations. In this embodiment, the feature image feature points are created by an image capturing device (not shown) to photograph the surrounding environment at a corresponding spatial position to obtain one or more images, and then Performing image analysis on the image or the content of the images, for example, analyzing road signs, signs, door numbers and door bodies fixed on the wall, or wall patterns and patterns, wall corner structures, or indicator symbols set on the ground, Directing the image features of the image of the object such as the line and the color of the tile to establish the feature points of the spatial image. However, in practice, since there are many ways to establish the spatial image feature points of a spatial position, the implementation is not limited thereto. .

The spatial positioning unit 34 is triggered by the positioning request, and the spatial image feature points existing in the front scene image 310 are currently obtained according to the spatial model to identify the spatial position corresponding to the front scene image 310. And get a current location. In addition, the spatial positioning unit 34 also compares the corresponding spatial location from the spatial map according to the location option of each target location in the navigation requirement.

The aisle recognition unit 35 has a walkway image feature point of the walkway image of the indoor space 700, and the front view image 310 can be analyzed according to the walkway image feature points to identify the walkway area in the front scene image 310. 311, and the distribution position of the aisle area 311 to obtain a walkway space data corresponding to the front scene image 310.

Since there are many techniques for image recognition using image feature points, and are not the improvement points of the present invention, they will not be described in detail.

The navigation planning control unit 36 has a plurality of navigation icons 360 and a plurality of navigation voices respectively corresponding to the navigation icons 360. Each navigation icon 360 is a line image, an arrow image, and/or a text symbol image that can be used to guide the direction of travel, and each navigation voice is a voice description material corresponding to the direction of travel represented by the navigation icon 360.

When the navigation initiation unit 33 issues the navigation request, if the navigation initiation unit 33 is activated in the automatic planning mode, the navigation planning control unit 36 analyzes the spatial mapping unit 34 according to the spatial map. The current location of the front scene image 310 is located, and the spatial positioning unit 34 analyzes the spatial locations identified by the target locations, and automatically plans a navigation route from the current location to the target locations. And further analyzing each spatial position along the navigation route, and comparing the spatial locations of the navigation route and the spatial models corresponding to the target locations, and comparing the plurality of spatial models respectively. The navigation icon 360 guiding the navigation route to the direction of travel through the spatial locations and the target locations, and comparing the navigation voice corresponding to each of the navigation icons 360.

In this embodiment, the navigation route established by the navigation planning control unit 36 in the automatic planning mode is a route having the shortest walking distance from the current location to the target locations, but when implemented, In another embodiment of the present invention, the navigation route may also be the route with the best travel convenience. Since the navigation route is planned in many ways and is not an improvement focus of the present invention, it will not be described in detail.

When the navigation request is to set the arrival sequence, the navigation planning control unit 36 plans the navigation route from the current location to the target locations in sequence according to the arrival order of the target locations, and compares the navigation routes. The spatial models, the navigation icons 360, and the navigation voices corresponding to the target locations are located along the navigation route.

The moving speed determining unit 37 analyzes changes in the appearance, movement, and/or disappearance of the plurality of image feature points that are sequentially positioned by the spatial positioning unit 34 over a period of time to obtain the movement of the electronic device 800 during the period of time. The speed, and when the moving speed is less than or equal to a speed threshold, triggers the navigation planning control unit 36 to re-plan to provide another navigation route for the user 600 to select.

The obstacle recognition unit 38 has a plurality of obstacle image feature points respectively representing a plurality of obstacles 701 that are disposed in the indoor space 700 to restrict passage, and the obstacle recognition unit 38 analyzes the front scene image 310. Whether or not the obstacle image feature points exist is present to determine whether the obstacle 701 is present. And when it is determined that the navigation route has one or more obstacles 701 in the traveling direction of the front scene image 310, the navigation planning control unit 36 is triggered to re-plan to provide another avoidable obstacle 701 to go to the target locations. Navigation route.

When the navigation planning control unit 36 re-plans the other navigation route, the electronic device 800 is driven to display a change route inquiry message corresponding to another navigation route, and the electronic device 800 is operated to inquire for the change route. When the message replies with a confirmation change message, the original navigation route is replaced by the other navigation route.

The model correction unit 39 is triggered to be activated during the navigation of the navigation planning control unit 36 according to a navigation route, and the spatial image feature points that are compared by the spatial positioning unit 34 according to the front scene image 310, and When there is a difference in the spatial image feature points of the spatial model of the spatial location currently scheduled to arrive, for example, an obstacle image feature point that does not exist originally, or one or more image features that should exist in the missing space At the time of the point, the spatial image feature points of the spatial model are replaced by the spatial image feature points existing in the front scene image.

When the indoor navigation system 3 of the present invention is used, if the user 600 wants to locate the current space location, the navigation activation unit 33 can be operated to issue the positioning request, and then the electronic device 800 can be placed to capture its traveling direction. The angular posture of the front view image. The image control unit 31 will start to drive the electronic device 800 to capture and display the front scene image 310. The spatial positioning unit 34 analyzes and obtains the spatial image feature points existing in the front scene image 310, and analyzes the spatial position corresponding to the front scene image 310 to obtain the current position. And driving the electronic device 800 to display, on the display 801, related information of the spatial location currently located for viewing.

When the user 600 wants to perform indoor navigation for one or more target locations, the navigation activation unit 33 can be operated to issue a navigation request for the predetermined target location, and when the navigation requires setting a plurality of target locations, the startup can be selected. The automatic planning mode, or initiating the manual planning mode, sorts the target locations by themselves to set the arrival order. The navigation planning control unit 36 plans the navigation route from the current location to the target locations according to the spatial map, and analyzes the spatial locations distributed along the traveling direction of the navigation route, and the spatial locations and The spatial models corresponding to the target locations, the navigation icons 360, and the navigation voices.

During the navigation of the indoor navigation system 3 according to the navigation route, the user 600 needs to continuously maintain the electronic device 800 in an angular posture capable of capturing a scene image in front of the traveling direction during the traveling, the image control unit. 31 continuously controls the electronic device 800 to capture and display the front scene image 310, so the current scene image changes as the user 600 holds the movement of the electronic device 800.

The spatial positioning unit 34 can analyze the current front scene image 310 to locate the spatial position corresponding to the current position according to the spatial models of the spatial positions that are to be passed by the navigation route, and at the same time, The walkway recognition unit 35 analyzes the front scene image 310 to obtain the walkway space data, and the navigation plan control unit 36 compares the navigation icon 360 corresponding to the current position with the navigation voice, and drives the image control unit 31 to The navigation area 360 in the front scene image 310 currently displayed by the electronic device 800 instantly displays the navigation icon 360, and synchronously drives the voice control unit 32 to control the electronic device 800 to play the navigation voice. Therefore, the user 600 can view the direction of the navigation icon 360 in the front scene image 310 displayed by the electronic device 800, and listen to the navigation voice content, and clearly know which direction to go forward, and can reach The purpose of instant augmented reality navigation in the indoor space 700.

In this embodiment, the spatial positioning unit 34 analyzes the currently received front scene image 310 by using the spatial model corresponding to the spatial position that the navigation route is to reach next to determine whether the electronic device 800 is Moved to the reserved location. However, in implementation, the spatial model of the plurality of spatial locations that are to be followed by the navigation route may be navigated to analyze the currently received front scene image 310 to determine whether the electronic device 800 has moved to the predetermined spatial location. Since the front scene image 310 is analyzed by the spatial model to have a large number of modes for locating the current position, the implementation is not limited to the above two methods.

When the spatial positioning unit 34 is unable to analyze the front scene image 310 by the spatial models of the spatial locations that the navigation route is about to reach to locate the current location, it indicates that the user 600 may have been displaced from the navigation route. At this time, the spatial positioning unit 34 analyzes the current front scene image 310 with the spatial models distributed at a plurality of spatial locations around the current position that was previously positioned, thereby relocating the electronic device 800. The current location is located, and the navigation plan control unit 36 re-plans another navigation route to the remaining target locations according to the current location currently located.

In addition, during the navigation of the indoor navigation system 3, the moving speed determining unit 37 continuously analyzes the changes in the appearance, movement, and/or disappearance of the plurality of image feature points that the spatial positioning unit 34 compares over a period of time. To obtain the moving speed of the electronic device 800 during the period of time, and when determining that the moving speed of the electronic device 800 is less than the speed threshold, driving the navigation planning control unit 36 to the currently positioned current position and not yet arrived. The remaining target locations re-plan a new navigation route, and the navigation planning control unit 36 drives the electronic device 800 to display a change route inquiry message on the display 801 for the user 600 to operate to select whether to accept the change navigation route. .

When the user 600 chooses to accept the change navigation route, the navigation plan control unit 36 replaces the original navigation route with the newly planned navigation route, and navigates according to the new navigation route. The navigation planning control unit 36 continues to perform the navigation operation on the original navigation route when the user 600 does not accept the operation selection.

Furthermore, the obstacle recognition unit 38 further analyzes whether there is an obstacle image feature point in the front scene image 310 corresponding to the current position during the navigation process, so as to determine whether the front scene image 310 is located in the front scene image 310. The obstacle 701 on the route is navigated, and when it is determined that the obstacle 701 is present on the navigation route, as shown in FIG. 3(A), the navigation plan control unit 36 is driven to re-plan a navigation route capable of avoiding the obstacle 701. The navigation planning control unit 36 compares the navigation icon 360 corresponding to the current location with the navigation voice according to the new navigation route, and then drives the image re-unit to control the electronic device 800 to display the corresponding image in the front scene image 310. The navigation icon 360 of the new navigation route is as shown in FIG. 3(B), and drives the voice control unit 32 to control the electronic device 800 to synchronously play the navigation voice corresponding to the new navigation route to guide the use. The person 600 travels in a direction away from the obstacle 701.

In addition, during the navigation process, the model correction unit 39 selects the spatial image feature points that are compared by the spatial positioning unit 34 according to the front scene image, and the space that is currently scheduled to arrive at the spatial position of the navigation route. There are some differences in the spatial image feature points of the model, for example, there is a 20% difference, and when it is not corresponding to the spatial model of any spatial position around the navigation route, the spatial position of the navigation route currently scheduled to arrive is determined. The spatial image feature points have been changed, and the spatial image feature points of the spatial model that replace the spatial position currently scheduled to arrive are corrected by the spatial image feature points existing in the front scene image.

In this embodiment, the image control unit 31 superimposes the navigation icon 360 on the aisle region 311 of the front scene image 310 by using the augmented reality technology. However, in implementation, another embodiment of the present invention The image control unit 31 does not display the navigation icon 360 in the aisle region 311 of the front scene image 310, and can be displayed on other parts of the front scene image 310, and can also achieve the function of guiding the traveling direction. .

In summary, the indoor navigation system 3 analyzes the spatial image feature points in the front scene image 310 that the electronic device 800 currently captures to perform the positioning of the indoor space 700, and can accurately locate the electronic device 800. Which spatial location of the indoor space 700 is located, and the navigation route from the current location to the target locations can be accurately planned, and the navigation icon 360 can be superimposed and displayed on the electronic in the augmented manner during the navigation process. The device 800 currently displays the front scene image 310, and drives the electronic device 800 to synchronously play the corresponding navigation voice, and can accurately guide the user 600 to walk in the indoor space 700 in an augmented reality instant navigation manner to go to the predetermined one. The target location is an innovative indoor navigation technology. Therefore, the object of the present invention can be achieved.

However, the above is only the embodiment of the present invention, and the scope of the invention is not limited thereto, and all the simple equivalent changes and modifications according to the scope of the patent application and the patent specification of the present invention are still Within the scope of the invention patent.

3‧‧‧ indoor navigation system

31‧‧‧Image Control Unit

310‧‧‧ Front scene image

311‧‧‧Aisle area

32‧‧‧Voice Control Unit

33‧‧‧Navigation starter unit

34‧‧‧ Spatial Positioning Unit

35‧‧‧Aisle identification unit

36‧‧‧Navigation planning control unit

360‧‧‧ navigation icons

37‧‧‧Moving speed judgment unit

38‧‧‧ obstacle recognition unit

39‧‧‧Model Correction Unit

600‧‧‧Users

700‧‧‧ indoor space

701‧‧‧ obstacles

800‧‧‧Electronic devices

801‧‧‧ display

802‧‧‧ Speaker

803‧‧‧ lens

Other features and advantages of the present invention will be apparent from the embodiments of the present invention, wherein: Figure 1 is a schematic diagram illustrating an embodiment of the indoor navigation system of the present invention implemented in an electronic device for indoor navigation FIG. 2 is a functional block diagram of the embodiment; and FIG. 3 is a schematic diagram of an image control unit of the embodiment superimposing a navigation icon in a scene before the display of an electronic device, wherein (A) is schematically illustrated Describe the situation when an obstacle appears in the direction of travel indicated by a navigation icon; (B) schematically illustrates the navigation route of the embodiment that re-plans to avoid the obstacle, and correspondingly changes the navigation icon displayed in the front scene image Happening.

Claims (10)

An indoor navigation system is adapted to be implemented in an electronic device, and the electronic device can be used for navigating an indoor space. The indoor navigation system includes: an image control unit capable of driving the electronic device to capture and display a front a scene image, and a navigation icon can be superimposed and displayed on the front scene image in an augmented reality manner; a navigation starting unit can set at least one target location to issue a navigation request; a spatial positioning unit stores one a spatial map corresponding to the indoor space, and a plurality of spatial models respectively corresponding to the plurality of spatial positions in the spatial map, each spatial model having a plurality of spatial image feature points, the spatial positioning unit issuing the same at the navigation starting unit Navigating the spatial image feature points of the front scene image currently displayed by the electronic device according to the spatial image feature points of the spatial model to locate the current spatial location of the electronic device to obtain a current Position, the spatial positioning unit can also compare the a spatial location corresponding to the target location; and a navigation planning control unit storing a plurality of navigation icons, and a navigation route from the current location to the spatial location corresponding to the at least one target location is planned according to the spatial map And at least one spatial location on the navigation route, and comparing the spatial models corresponding to the spatial location of the at least one spatial location on the navigation route corresponding to the at least one target location; When the navigation is started, the spatial positioning unit analyzes the front scene image to locate the current position according to the spatial model of the navigation planning control unit, and the navigation planning control unit compares one to guide the navigation route. The navigation icon corresponding to the direction of travel in the front scene image corresponding to the current position, and driving the image control unit to superimpose and display the compared navigation icon on the front scene image. The indoor navigation system of claim 1, wherein the navigation planning control unit further analyzes a plurality of spatial locations along the navigation route according to the spatial map, and compares the plurality of corresponding spatial positions. a spatial model, and a plurality of navigation icons respectively corresponding to the spatial positions, when the navigation is started, the spatial positioning unit analyzes the front scene image according to the spatial model of the navigation planning control unit to locate the current position. The navigation planning control unit compares the navigation icon corresponding to the current location. The indoor navigation system of claim 2, further comprising a walkway recognition unit that analyzes and identifies the walkway area in the front scene image to obtain a walkway space data, and the image control unit uses the walkway space data to guide the navigation The icons are superimposed on the walkway area in the front scene image. The indoor navigation system of claim 2, further comprising a model correction unit, wherein the spatial correction unit compares the spatial image feature points that are compared by the spatial positioning unit according to the front scene image, and the current navigation route When there is a difference in the spatial image feature points of the spatial model at a spatial location scheduled to arrive, the space exists in the front scene image The image feature point correction replaces the original spatial image feature points of the spatial model. The indoor navigation system of claim 1, 2, 3 or 4, wherein the navigation planning control unit further stores a plurality of navigation voices respectively corresponding to the navigation icons, and the navigation is compared according to the current comparison. The icon is compared with the corresponding navigation voice, and the indoor navigation system further includes a voice control unit, and the voice control unit synchronously controls the image control unit to control the electronic device to display the navigation icon on the front scene image. The electronic device plays and outputs the navigation voice that is compared by the navigation planning control unit. The indoor navigation system of claim 1, 2, 3 or 4, wherein the indoor navigation system further comprises a moving speed determining unit, wherein the moving speed determining unit analyzes the spatial positioning unit for comparison within a period of time The occurrence, movement, and/or disappearance of the plurality of image feature points to obtain a moving speed of the electronic device during the period of time, and triggering the navigation planning control when the moving speed is less than or equal to a speed threshold The unit re-planning provides another navigation route, and the navigation planning control unit drives the electronic device to display a change route inquiry message corresponding to another navigation route, and receives a confirmation change sent back to the change route inquiry message. In the case of a message, the original navigation route is replaced by the other navigation route. The indoor navigation system according to claim 1, 2, 3 or 4, further comprising an obstacle recognition unit, wherein the obstacle recognition unit has a plurality of built-in plurality of representations respectively arranged in the indoor space to restrict passage An obstacle image feature point of the obstacle, the obstacle recognition unit analyzes whether the front scene image has the obstacle image feature points to determine whether the obstacle exists. Blocking the object, and determining that there is an obstacle in the direction of travel of the navigation route in the front scene image, triggering the navigation planning control unit to re-plan to provide another navigation that can avoid the obstacle to go to the at least one target location a route, and the navigation planning control unit compares the navigation icon to guide the direction of travel of the other navigation route to the current location, and drives the image control unit to compare the navigation route to the other navigation route. The navigation icon is displayed in the front scene image. The indoor navigation system of claim 1, 2, 3 or 4, wherein the navigation activation unit is configured to set a plurality of target locations in the navigation request, and the navigation planning control unit plans the current location according to the spatial map. Location to the navigation route for these target locations. The indoor navigation system of claim 8, wherein the navigation request is configured with a plurality of target locations, and the navigation initiation unit has an automatic planning mode and a manual planning mode that can be selected to be activated, and the manual is When the planning mode is started, the target location can be arranged to operate to set an arrival order in the navigation requirement. When the navigation initiation unit starts the automatic planning mode, the navigation planning control unit automatically plans the current location according to the spatial map. Positioning the navigation route to the target locations, and when the navigation request is set to the arrival order, according to the arrival order of the space map and the navigation request, planning the order from the current location to the target locations Navigation route. The indoor navigation system of claim 1, 2, 3 or 4, wherein each navigation icon is a line image, an arrow image, and/or a text symbol image that can be used to indicate the direction of travel of the navigation route.