KR20150124112A - Method for Adaptive LOD Rendering in 3-D Terrain Visualization System - Google Patents

Abstract

The present invention relates to an adaptive rendering method in visualizing a 3D terrain image. The adaptive rendering method comprises: a data building step of building terrain mesh data; a static rendering step of rendering the terrain mesh data according to a detailed level value based on a terrain; a skip level setting step of setting a skip level; and a dynamic rendering step of rendering the terrain mesh data by dynamically changing a vertex coordinate of a polygon while maintaining resolution of the 3D terrain image according to the set skip level. Therefore, the adaptive rendering method minimizes lowering of real time visualization quality of the 3D terrain image.

Description

[0001] The present invention relates to an adaptive rendering method for three-dimensional terrain image visualization,

The present invention relates to an adaptive rendering method in 3D terrain image visualization, and more particularly, to an adaptive rendering method in 3D terrain image visualization, in which a static detail level scheme and a dynamic detail level are variably applied based on a reference frame rate value, The present invention relates to an adaptive rendering method in a three-dimensional terrain image visualization capable of minimizing visual quality degradation of a 3D terrain image.

The 3D Geographical Information System (GIS) represents real ground facilities and underground objects at the same time in digital elevation model (DEM) or digital terrain model (DTM) And it is possible to continuously manage the location information of the ground facilities or underground objects.

In particular, 3D GIS technology has been applied to general areas such as urban landscape planning, disaster management system, navigation, SNS service, and big data analysis as well as searching for and modifying the location of ground facilities or underground objects, assuming that the real world is ultimately 3D The application target is gradually expanding.

In this way, it takes a lot of time and cost to construct 3D data, and in order to operate the data on a mobile device, a higher specification equipment is required.

Recently, as a virtual reality system, a computer game, and the like have rapidly developed, techniques for expressing three-dimensional objects and terrain of a real world using a computer system have been researched and developed. A mesh model is a typical technique for representing the real world as a three-dimensional image on a computer.

A mesh model consists of a set of interconnected triangles, squares or polygons to represent a three-dimensional surface such as an object or a terrain. In order to represent large-scale data such as large-scale terrain in a computer system three-dimensionally by using a mesh model, proper terrain generation, management and presentation techniques are required to effectively use limited graphic resources of a computer system.

To this end, technologies such as PM (Progressive Mesh) -based technology, DEM (Digital Elevation Model) and ROAM (Real-time Optimally Adaptive Meshes) technology have been provided. Especially, polygon based rendering method using DEM technology can represent 3D object and terrain of real world using triangles.

In the conventional polygon-based rendering technology, a parent node or a child node is created according to the rendering level set by the level setting means by loading the terrain and the image mesh data, and the mesh of the node is rendered in detail according to the rendering means. So that the 3D terrain data can be visualized in real time.

At this time, a general 3D visualization detail level setting method is roughly divided into a static detail level (SLOD) and a dynamic detail level (DLOD) according to a data storage method, Based detailed level (LOD) and area-based detailed level according to the value calculation method.

Based on the distance-based detailed level and the area-based detailed level, the LOD level value is obtained by calculating the distance value or the area of the topography between the point of view and the center point of the tile of the tile to be represented as a reference for setting the LOD level value.

The static detail level method visualizes and displays a list of indexes to be expressed according to the level combination of the patches close to their own levels calculated according to the distance. This method requires a lot of memory because the load of the processor is small but all data must be prepared by the preprocessing.

On the other hand, the dynamic detail level method is a method of dynamically visualizing data according to the LOD level value of each terrain, which allows detailed control as compared with the static detail level method. However, the load of the processor must be increased correspondingly, So that the bottleneck of the processor may occur.

When the static detail level method is applied to the mobile terminal, it takes a lot of data load, and when the dynamic detailed level method is applied to the mobile terminal, it takes a lot of processor load, There is a problem.

As prior art data, Korean Patent Laid-Open Publication No. 2010-0060194 describes techniques for point-based rendering methods and devices in navigation devices.

The conventional point-based rendering method and apparatus include a process of generating a point of a grid structure using altitude information included in DEM terrain data, a process of determining a size of a rectangular splat generated around the point, The rendering speed can be improved since the number of primitives is generated by the inter-grid intersection of the DEM data, including the process of rendering the 3D terrain using a rectangular splat of the size.

The conventional point-based rendering method and apparatus is a rectangular spattle modeling a three-dimensional height value expressed by a DEM using a simple linear interpolation method, and is suitable for flat modeling because it is fast and simple. However, It is difficult to accurately express the feature in the image.

In addition, since the conventional point-based rendering method and apparatus are composed of a very large number of grid points in the case of complicated terrain, a preprocessing procedure for simplifying all vertex information for LOD control should be performed. This preprocessing procedure requires a large amount of memory because it requires a large amount of calculation, and there is a problem that high-end equipment must be used for fast operation processing.

Korean Patent Publication No. 2010-0060194 "Point-Based Rendering Method and Apparatus in Navigation Device"

The present invention can reduce the real-time visual quality degradation of a 3D terrain image by applying a static detail level scheme to the texture level itself and applying the dynamic detail level scheme so that the vertex information is changed according to the reference frame rate value An adaptive rendering method in 3D terrain visualization is provided.

Among the embodiments, the adaptive rendering method in the 3D terrain image visualization includes a data construction step of constructing terrain mesh data composed of the divided topographic tiles by dividing the terrain into tiles based on the topographic data of the area to be visualized; A plurality of vertex coordinates of the polygon are calculated in a terrain tile constituting a plurality of polygons, vertex information is stored, and a level of detail of the three-dimensional terrain of the terrain mesh data is calculated according to a user's viewpoint A static rendering step of loading the terrain mesh data corresponding to the position information according to the change of the user's view point and rendering the terrain mesh data according to the detailed level value according to the terrain; Dimensional terrain image of a preset resolution by performing image mapping for every vertex in the terrain tile, measuring the number of frames to be reproduced per predetermined time, and when the number of frames measured is equal to or less than a preset reference frame value, A skip level setting step of setting a skip level so that the number of polygons within the polygon is reduced; And a dynamic rendering step of dynamically varying the vertex coordinates of the polygon while maintaining the resolution of the 3D terrain image according to the set skip level to render the terrain mesh data.

The skip level setting step sets the skip level to '0' when the number of frames measured is equal to or greater than a preset reference frame value, and transmits the vertex information to the dynamic rendering step so that an N × N mesh is visualized .

The skip level setting step sets the skip level to '1' when the measured number of frames is equal to or less than the predetermined reference frame value, and applies the skip level '1' to the M × M (M <N) And transmits the vertex information corresponding to the M × M mesh to the dynamic rendering step so as to be visible.

Wherein the skip level setting step measures a number of frames to be reproduced per a predetermined time while the M 占 메시 mesh whose skip level is set to '1' is visualized and skips the frame if the measured number of frames is equal to or less than a preset reference frame value Level is set to '2', and vertex information corresponding to the L × L mesh is transmitted to the dynamic rendering step so that the L × L mesh is visualized by applying the skip level '2'.

Wherein the skip level setting step adjusts the skip level in one of an automatic setting method and a fixed setting method so that the number of polygons in the terrain tile is increased when the measured number of frames is upward and equal to or greater than the reference frame value .

The adaptive rendering method in the 3D terrain image visualization of the present invention applies the static detail level scheme to the texture level itself and applies the dynamic detail level scheme to vary the vertex information according to the reference frame rate value, It is possible to minimize degradation of real-time visualization quality of the terrain image.

In addition, the present invention can improve the rendering speed by reducing the number of polygons according to the skip level while maintaining the resolution of the 3D terrain image at a high resolution, It is possible to secure a frame rate higher than the frame rate value, which can improve map operation and productivity, and can be applied to mobile terminals and low-end equipment.

1 is a view for explaining the configuration of an adaptive rendering system in 3D terrain image visualization according to an embodiment of the present invention.
2 is a flowchart illustrating an adaptive rendering method in 3D terrain image visualization according to an exemplary embodiment of the present invention.
FIG. 3 is a view showing a change state of a polygon according to a skip level applied to FIG. 2. FIG.
4 is a diagram illustrating an example of a 3D terrain image using the number of vertexes of an existing LOD.
5 is a diagram illustrating an example of a 3D terrain image to which a skip level is applied according to an embodiment of the present invention.

The description of the present invention is merely an example for structural or functional explanation, and the scope of the present invention should not be construed as being limited by the embodiments described in the text. That is, the embodiments are to be construed as being variously embodied and having various forms, so that the scope of the present invention should be understood to include equivalents capable of realizing technical ideas. Also, the purpose or effect of the present invention should not be construed as limiting the scope of the present invention, since it does not mean that a specific embodiment should include all or only such effect.

Meanwhile, the meaning of the terms described in the present invention should be understood as follows.

The terms "first "," second ", and the like are intended to distinguish one element from another, and the scope of the right should not be limited by these terms. For example, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component.

It is to be understood that when an element is referred to as being "connected" to another element, it may be directly connected to the other element, but there may be other elements in between. On the other hand, when an element is referred to as being "directly connected" to another element, it should be understood that there are no other elements in between. On the other hand, other expressions that describe the relationship between components, such as "between" and "between" or "neighboring to" and "directly adjacent to" should be interpreted as well.

It should be understood that the singular " include "or" have "are to be construed as including a stated feature, number, step, operation, component, It is to be understood that the combination is intended to specify that it does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

In each step, the identification code (e.g., a, b, c, etc.) is used for convenience of explanation, the identification code does not describe the order of each step, Unless otherwise stated, it may occur differently from the stated order. That is, each step may occur in the same order as described, may be performed substantially concurrently, or may be performed in reverse order.

All terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, unless otherwise defined. Commonly used predefined terms should be interpreted to be consistent with the meanings in the context of the related art and can not be interpreted as having ideal or overly formal meaning unless explicitly defined in the present invention.

1 is a view for explaining the configuration of an adaptive rendering system in 3D terrain image visualization according to an embodiment of the present invention.

1, an adaptive rendering system 100 in a 3D terrain visualization includes a terrain generation module 110, an LOD module 120, a rendering module 130, an image mapping module 140, and a database 150 , But it is not limited thereto and includes a display means, an input means, a buffer, a CPU, and the like provided in a three-dimensional terrain image visualization system in general.

The terrain generation module 110 acquires the terrain data of the area to be visualized according to the input data of the user and divides the 3D terrain into terrain tiles to construct the terrain mesh data composed of the divided terrain tiles. At this time, the terrain generation module 110 may adjust the number of tiles and the size of the tiles constituting the three-dimensional terrain according to the user setting.

The LOD module 120 calculates and stores a plurality of vertex coordinates of each polygon in a terrain tile constituting a plurality of polygons, and calculates a detailed level value of the three-dimensional terrain of the terrain mesh data corresponding to the corresponding position information And polygons converted into a two-dimensional coordinate system (for example, UV coordinate system) serving as a conversion reference are assigned to the tiles and prepared for rendering so as to texture the polygons in the three-dimensional space according to the detailed level value.

The UV coordinate system is a coordinate system for associating the image and the surface of the image when performing the image mapping, and is a coordinate that sets the relative position of the image separately for all the points constituting one surface of the terrain.

In order to smoothly manage large-sized data such as satellite images and aerial images in a 3D visualization system, the LOD divides one terrain data into several levels of resolution, and then displays the terrain mesh data at an appropriate resolution according to the user's viewpoint position to be.

A polygon is a polygon that is the smallest unit used to represent a three-dimensional shape in a three-dimensional terrain. A polygon is a polygon whose start and end points are connected by lines in a three-dimensional space. Is used to indicate the edge of the frame. Therefore, when the 3D terrain model is modeled, it is possible to obtain a faster processing speed without deteriorating the picture quality by variably adjusting the number of polygons considering the change of the position of the user point.

The rendering module 130 sets a detailed level by applying a texture level (SLOD) method to the texture image, applies a DLOD (Dynamic Level Of Detail) method to the vertex coordinates of the polygon according to the reference frame (FPS) . The rendering module 130 sets a detailed level value for the terrain mesh data according to the user's point of view, loads the terrain mesh data, and performs rendering according to the set detailed level value.

The image mapping module 140 provides a more realistic and realistic three-dimensional topographic image by applying an actual three-dimensional topographic image to the outer surface of the polygon when the three-dimensional polygon is visualized.

The database 150 indexes and stores the terrain data, the terrain mesh data, and the 3D terrain image, respectively, and stores the terrain data, the terrain mesh data, and the 3D terrain image according to categories according to a predetermined classification system.

FIG. 2 is a flowchart for explaining an adaptive rendering method in 3D terrain image visualization according to an embodiment of the present invention, and FIG. 3 is a diagram illustrating a change state of a polygon according to a skip level applied in FIG.

2 and 3, in the adaptive rendering method in the 3D terrain image visualization, the terrain mesh data composed of each divided terrain tile is constructed by dividing the terrain into tiles based on the terrain data of the visualization target area And stores it in the database 150. (S1)

The adaptive rendering system 100 calculates a plurality of vertex coordinates of each polygon in a terrain tile constituting a plurality of polygons and stores the vertex coordinates in the database 150 as vertex information. The LOD module 120 calculates the level of detail of the three-dimensional topography of the terrain mesh data according to the user's point of view and controls the level of the mesh to be adjusted in stages.

The rendering module 130 applies a SLOD (Static Level Of Detail) method to the texture level and applies a DLOD (dynamic LOD) method so that the vertex coordinates dynamically change according to the FPS value.

In this case, the SLOD calculates the vertex information corresponding to the LOD value in advance, and a precise mesh is used for an object located close to the camera in the state where the accuracy of the mesh is determined from the beginning, and as the distance between the camera and the object becomes longer, Mesh is used to process the LOD value of each terrain at rendering time. And, DLOD can change the precision of real-time mesh according to the distance to prevent popping phenomenon and enable detailed control.

That is, the rendering module 130 loads the terrain mesh data corresponding to the position information according to the change of the user view point and renders the terrain mesh data according to the detailed level value according to the terrain (S3)

 The adaptive rendering system 100 designates the skip level as '0', and causes the N × N mesh, which is a 3D terrain image having a resolution of 256 × 256, to be visualized on the screen (S4) .

The adaptive rendering system 100 measures the frame per second (FPS) in order to respond faster to user response when the 3D visualization is not finished (S5 and &lt; RTI ID = 0.0 &gt; S6)

The adaptive rendering system 100 designates the skip level to '1' so that the number of polygons in the terrain tile is reduced when the measured FPS value is less than or equal to the reference FPS value, and causes the M × M mesh to be visualized on the screen. (S7 and S8 ) Where M can be 33.

Generally, a user recognizes that the screen is smooth when the number of frames per second is at least 10 or more. Therefore, the skip level can be forcibly changed from '0' to '1' when the current measured FPS value is less than 10 under the assumption that the reference FPS value is set to 10 and the 3D terrain image is continuously visualized.

At this time, when the skip level is adjusted from '0' to '1', the rendering module 130 uses 256 × 256 as the resolution of the 3D terrain image and uses the vertex information of the polygon as the vertex corresponding to the N × N mesh It passes vertex information corresponding to M × M mesh, not information.

FIG. 3 (a) shows a 65 × 65 mesh designated by a skip level '0', FIG. 3 (b) shows a 33 × 33 mesh with a skip level of '1' The 17 x 17 mesh designated by this '2' is shown.

Referring to FIG. 3, it can be seen that the number of polygons is greatly reduced according to a skip level in a 3D terrain image. As described above, if the number of polygons is reduced, the rendering speed is improved. As a result, the frame rate (FPS) of the 3D terrain image becomes very high, so that the 3D terrain image can be displayed smoothly with discontinuity.

The adaptive rendering system 100 measures the FPS while the M × M mesh whose skip level is set to '1' is being visualized on the screen, and changes the skip level from '1' to '2' when the measured FPS value is less than the reference FPS value. (S9, S10, S11). Here, L can be 17.

Meanwhile, the adaptive rendering system 100 measures the FPS while the L × L mesh whose skip level is set to '2' is visualized on the screen, and when the FPS value is upwardly rendered smoothly, the skip level is set to '1' So that the M × M mesh is displayed on the screen.

At this time, the adaptive rendering system 100 may cause the skip level to be automatically adjusted up or down according to the FPS value, and may be fixed to a specific skip level regardless of the FPS value.

In the case where the skip level is 65 占 65 meshes for the 0 level, 33 占 33 meshes for the 1 level, 17 占 17 meshes for the 2 levels, 9x9 meshes for the 3 levels, and 4 levels 5 x 5 meshes, and 3 x 3 meshes in the case of 5 levels.

However, a screen that is visible when the skip level is two or more levels is displayed in a substantially flat state. If the skip level is at the 0 level, it is almost flat from the 3rd level. Therefore, the visualization effect of the 3KCKDNJS terrain image falls exponentially and the meaning of 3D rendering is lost.

Accordingly, the adaptive rendering system 100 can increase the number of levels by setting the skip level to 0 level to 5 level or subdividing the level according to the mesh size, but in order to improve the visualization effect of the 3D terrain image, Can be adjusted at 0 level, 1 level, and 2 level.

As described above, the adaptive rendering system 100 can smoothly express the 3D terrain image by performing the adaptive rendering method until the 3D terrain image visualization is completed by the user command.

When the adaptive rendering system 100 needs to express a lot of ground facilities or underground objects rather than a flat terrain, if the FPS value is reduced to a frame of 5 or less, the skip level is applied and the frame can be significantly improved, So that the 3D terrain image visualization system can be operated. At this time, the adaptive rendering system 100 may vary the enhancement rate of the visualized frame according to the graphics performance of the mobile system.

The 3D terrain image simultaneously displays real ground facilities and underground objects with digital elevation model (DEM) data representing the topography or topography numerically, and stores the DEM data in the database 150.

Table 1 shows the number of vertices of the existing LOD and the resolution, and FIG. 4 is an illustration for explaining a 3D terrain image using the number of vertices of the existing LOD.

(A) 256 × 256 resolution image, (b) 128 × 128 resolution image, and (c) 64 × 128 resolution image as shown in Table 1 and FIG. × 64 resolution image is outputted, and the resolution and the number of vertices of the image are different according to the LOD value.

Table 2 shows the number of vertices and resolution of the adaptive LOD according to an exemplary embodiment of the present invention, and FIG. 5 is an exemplary view illustrating a 3D terrain image to which a skip level is applied according to an embodiment of the present invention.

As shown in Table 2 and Fig. 5, (a) an original image, (b) a 65x65 mesh screen and (c) a 33x33 mesh screen are output, and the adaptive LOD displays a 65x65 mesh screen And the 33x33 mesh screen are visualized differently.

Table 3 shows the FPS comparison values between the existing LOD and the adaptive LOD.

As shown in Table 3, when the skip level is set to '2', the frame rate of the device C is improved from 5FPS to 10FPS, and the frame rate of the information C is doubled.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention as defined by the following claims It can be understood that

110: terrain generation module 120: LOD module
130: Rendering module 140: Image mapping module
150: Database

Claims (5)

A data constructing step of constructing a topography mesh data composed of the divided topographic tiles by dividing the topography into tiles based on the topographic data of the visualization target area;
A plurality of vertex coordinates of the polygon are calculated in a terrain tile constituting a plurality of polygons, vertex information is stored, and a level of detail of the three-dimensional terrain of the terrain mesh data is calculated according to a user's viewpoint A static rendering step of loading the terrain mesh data corresponding to the position information according to the change of the user's view point and rendering the terrain mesh data according to the detailed level value according to the terrain;
Dimensional terrain image of a preset resolution by performing image mapping for every vertex in the terrain tile, measuring the number of frames to be reproduced per predetermined time, and if the measured number of frames is less than a preset reference frame value, A skip level setting step of setting a skip level so that the number of polygons within the polygon is reduced; And
And a dynamic rendering step of dynamically varying the vertex coordinates of the polygon while maintaining the resolution of the 3D terrain image according to the set skip level to render the terrain mesh data. In an adaptive rendering method.
2. The method of claim 1, wherein the skip level setting step comprises:
Wherein the skip level is set to '0' when the number of frames measured is equal to or greater than a predetermined reference frame value, and the vertex information is transmitted to the dynamic rendering step so that an N × N mesh is visualized. Adaptive rendering method in image visualization.
3. The method of claim 2, wherein the skip level setting step comprises:
(M &lt; N) mesh is visualized by setting the skip level to '1' and applying the skip level '1' when the measured number of frames is equal to or less than a preset reference frame value, And the vertex information corresponding to the vertex information is transmitted to the dynamic rendering step.
4. The method of claim 3, wherein the skip level setting step comprises:
The number of frames to be reproduced per predetermined time is measured while the M × M mesh having the skip level of '1' is visualized. If the measured number of frames is equal to or less than a predetermined reference frame value, the skip level is set to '2' , And transmits the vertex information corresponding to the LxL mesh to the dynamic rendering step so that the LxL mesh is visualized by applying the skip level '2' to the dynamic rendering step. Way.
2. The method of claim 1, wherein the skip level setting step comprises:
Wherein the skip level is adjusted by one of an automatic setting method and a fixed setting method so that the number of polygons in the terrain tile is increased when the measured number of frames is upward and equal to or greater than the reference frame value. In an adaptive rendering method.

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