Patent Application
20060132488
The present application is based on, and claims priority from, Korean Application Number 2004-00107657, filed Dec. 17, 2004, and 2005-0061731, filed Jul. 8, 2005 the disclosure of which is hereby incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to a computer graphic system, and more particularly, to an apparatus and a method for representing a three-dimensional model with a vast amount of data such as a large-scale terrain model in a computer system in real time.
2. Description of the Related Art
Recently, a rapid advancement of computer graphic fields such as a virtual reality system and a computer game has led to a development of various methods to represent numerous objects in the real world and terrain in three dimensions. A mesh model has been mainly employed to represent three-dimensional objects of the real world in a computer system. The mesh model particularly represents three-dimensional surfaces of objects or terrain using a collection of a plurality of triangles, tetragons or polygons which are correlated with each other.
For a three-dimensional representation of a vast amount of data such as a large-scale of terrain in a computer system in real time using the mesh model, specific techniques of generating, managing and representing proper terrain are required to effectively utilize limited graphic resources of the computer system. A progressive mesh (PM) based technique, a digital elevation model (DEM) and real-time optimally adaptive meshes (ROAM) are conventional techniques of representing a vast amount of terrain data in real time. These conventional techniques are applied to various fields of computer graphics, virtual reality and a geographical information system (GIS).
In U.S. patent application Ser. No. 6,611,267 issued to A. Migdal et al., entitled “System and Method for Computer Modeling of 3D Objects or Surfaces by Mesh Construction Having Optimal Quality Characteristics and Dynamic Resolution Capabilities,” a three-dimensional modeling method and a system for objects or surfaces using the PM based technique are introduced. The PM based technique configures the mesh model dynamically by determining the order of inserting vertices of polygons within the mesh and gradually inserting the vertices, and thus, the mesh can be always maintained optimally. Also, managing the list including information on the insertion and the removal makes it possible to rapidly remove vertices from the mesh. However, the PM based technique needs to modify the mesh model dynamically to represent three-dimensional images. Hence, the PM based technique generally takes up a large portion of a memory and has a slow data representation rate.
The ROAM technique is discribed in an article by Duchaineau et al., entitled “ROAMing Terrain: Real-Time Optimally Adapting Meshes,” IEEE Visualization on '97 Proceedings, pp. 81-88, 1997. The ROAM technique configures a binary tree of triangls to minimize the reconfiguration of a mesh processed in real time and is optimized by combining a gradual division of the triangle with a deferred list of priority rank calculation. However, the ROAM technique needs to dynamically reconfigure the mesh with various ranges of resolution to represent three-dimensional images. As a result, the ROAM technique may not be proper to a large-scale terrain system, which requires rapid terrain representation.
Accordingly, the present invention is directed to an apparatus and a method for representing a multi-level LOD three-dimensional image that substantially obviates one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an apparatus for reconfiguring a large-scale terrain data in a computer system without taking up a large portion of a memory and a large amount of computation and representing the reconfigured large-scale terrain data, and a method therefor.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
According to an aspect of the present invention, there is provided an apparatus for representing a three-dimensional image with a multi-level LOD (level of detail), including: a patch configuration unit configuring a multi-level LOD hierarchical mesh for each hierarchical level with a different LOD level by arranging triangular patches of a higher level (level m+1, lower resolution) to have approximately k×k of triangular patches of an lower level (level m, higher resolution), where k is the number of horizontal and vertical grids at the lower level and sampling information on height of a target image on a regular basis to allocate the sampled height information to each vertex of the triangular patches included in the multi-level LOD hierarchical mesh; an LOD determination unit determining an LOD of each triangular patch according to a view point of a virtual camera; and a patch connection unit connecting the adjacent triangular patches with each other without gaps when the adjacent triangular patches among the triangular patches of the multi-level LOD hierarchical mesh have different LOD levels.
According to an another aspect of the present invention, there is provided a method for representing a three-dimensional image with a multi-level LOD (level of detail), including the steps of: configuring a multi-level LOD hierarchical mesh for each hierarchical level with a different LOD level by arranging triangular patches of a higher level (level m+1, lower resolution) to have approximately k×k of triangular patches of an lower level (level m, higher resolution), where k is the number of horizontal and vertical grids of the lower level; sampling information on height of a target image on a regular basis and allocating the sampled height information to each vertex of the triangular patches included in the multi-level LOD hierarchical mesh; determining an LOD of each triangular patch according to a view point of a virtual camera; and connecting the adjacent triangular patches with each other without gaps when the adjacent triangular patches among the triangular patches of the multi-level LOD hierarchical mesh have different LOD levels.
According to a further aspect of the present invention, there is provided a computer readable recording medium on which a program is used for implementing a method for representing a multi-level LOD three-dimensional image, the computer readable recording medium including: configuring a multi-level LOD hierarchical mesh for each hierarchical level with a different LOD level by arranging triangular patches of a upper level (level m+1, lower resolution) to have approximately k×k of triangular patches of an lower level (level m, higher resolution), where k is the number of horizontal and vertical grids of the upper hierarchical level; sampling information on height of a target image on a regular basis and allocating the sampled height information to each vertex of the triangular patches included in the multi-level LOD hierarchical mesh; determining an LOD of each triangular patch according to a view point of a virtual camera; and connecting the adjacent triangular patches with each other without gaps when the adjacent triangular patches among the triangular patches of the multi-level LOD hierarchical mesh have different LOD levels.
It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:
FIGS. 7(a) to 7(g) are diagrams illustrating a method for connecting adjacent patches having different LOD levels without gaps according to an embodiment of the present invention;
FIGS. 8(a) to 8(d) are diagrams illustrating a method for connecting patches when 2 triangular patches of an higher resolution are arranged adjacent to one selected triangular patch of a lower resolution;
Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. It should be noted that like reference numerals denote like elements even in different drawings. When describing the preferred embodiments, detailed description of related known functions or configuration will be omitted if being determined to confuse the main point of the present invention.
The apparatus 10 includes a patch configuration unit 11, an LOD determination unit 12 and a patch connection unit 13, and is connected to an input device 20 and a display device 30.
The input device 20 provides a target image to be represented on the display device 30 to the apparatus 10. Although the target image is mainly applied with a vast amount of data such as a terrain model, the target image is not limited to the terrain model; rather, the target image can be any images such as objects and surfaces that can be represented three-dimensionally. For instance, in the case of the terrain model, the target image can use scanned images by satellites or air planes, or a terrain model produced by a user.
As illustrated in
The hierarchical mesh is specifically configured to have a multi-level LOD with use of the triangular patches. The hierarchical mesh can be obtained by performing sequential operations of: configuring a two-dimensional square mesh with evenly spaced grids; and dividing each grid in the direction from a top right point of the grid to a bottom left point of the grid to obtain triangular patches constructing isosceles right triangles. The isosceles right triangles denoted with dots configure one patch with the highest LOD. At this point, there are k×k of isosceles right triangles, where k represents the number of vertical and horizontal grids of level m. The k×k number of the patches of level m are collected to configure triangular patches each at the LOD level of m+1.
The LOD determination unit 12 determines an appropriate LOD level according to a view point of a current virtual camera to represent the multi-level target image, which is constructed in precedent processes employing the patch configuration unit 11, on the display device 30 in real time. In the assumption that a virtual character exists within a three-dimensional virtual space constructed in a computer system, the view point of the current virtual camera is a view point of the virtual character seeing the virtual space. As a method for determining the LOD level for the target image according to the view point of the current virtual camera, a method of determining the LOD level according to an error of each triangular patch at a screen and a method of determining the LOD level according to a distance between the vertex of each triangular patch and the virtual camera.
Particularly, the illustrated diagram in
The patch connection unit 13 makes a connection between hierarchically constructed triangular patches with different LOD levels without a gap. The hierarchical mesh according to the present embodiment described in
FIGS. 7(a) to 7(g) are diagrams illustrating connection methods for removing gaps generated between adjacent patches with different LOD levels according to an embodiment of the present invention. Those dotted regions in FIGS. 7(a) to 7(g) are one level lower than that of those regions without being dotted.
FIGS. 7(b) to (d) illustrate an inter-patch connection method when two triangular patches of an upper hierarchical level are arranged closely to one triangular patch of a lower hierarchical level. In this case, vertices of unit triangular patches included in the triangular patches of the upper hierarchical level, being disposed in the boundaries between the triangular patches of the upper hierarchical level and the triangular patch of the lower hierarchical level, are connected consecutively in the form of zigzags, so that gaps generated between the adjacent triangular patches with different LOD levels can be removed. For instance, as illustrated in
Referring to
Referring to
Referring to FIGS. 8 (C) and 8(d), the third vertex is connected with a fourth vertex allocated at a side facing the third vertex among vertices of the unit triangular patches of the second triangular patch, so that gaps between the triangular patches with different LOD levels can be removed.
The illustrated multi-level LOD terrain is obtained by sequential operations of: determining an LOD based on a screen error using the LOD determination unit 12; and connecting adjacent patches with different LOD levels using the patch connection unit 13 according to the method described in FIGS. 7(a) to 7(g). As described above, the adjacent patches are connected without gaps between them. The final hierarchical mesh configured without gaps according to the present embodiment renders patches with a low LOD level with priority. That is, the rendering activity takes place in the order of the level n, the level n−1, . . . , and the level 1. At this point, the hierarchical levels lower than the patches of the current hierarchical level should not be included in the final hierarchical mesh. For instance, if the current hierarchical level of the rendered patches is m, the patches of less than or equal to level m+1 should not be included in the final hierarchical mesh.
In operation 101, using the patch configuration unit 11 of the apparatus 10, triangular patches of a lower hierarchical level (e.g., an level m+1) are configured to include approximately k×k of triangular patches of an upper hierarchical level (e.g., an level m), where k is the number of horizontal and vertical grids of the highest LOD hierarchical level. Each hierarchical level configures the multi-level LOD hierarchical mesh with different LOD levels. The patch configuration unit 11 also regularly samples information on height of a target image such as a terrain model inputted from the input device 20 and allocates the sampled height information to each vertex of the triangular patches of the hierarchical mesh.
In operation 102, an LOD level for each triangular patch of the hierarchical mesh is determined according to a view point of a virtual camera. As described in
In operation 103, it is determined whether all triangular patches of the hierarchical mesh are represented. If the representation is completed, this operation stage is terminated, and if otherwise, next operation stages proceed.
In operation 104, it is determined whether one triangular patch selected among the several triangular patches of the hierarchical mesh has the same LOD level as the adjacent triangular patch.
In operation 105, if the selected triangular patch has the same LOD level, the triangular patch is represented with a currently set LOD level. If otherwise, an operation stage of ‘A’ proceeds.
The above operation stages from 103 to 105 are repeated for the rest triangular patches until the representation of the hierarchical mesh is completed.
The operation stage 106 proceeds when it is determined that the selected triangular patch has a different LOD level from the adjacent triangular patch in operation 104 described in
If the selected triangular patch has a lower level, in operation 107, the selected triangular patch is represented with a currently set LOD level.
If it is determined that the selected triangular patch (corresponding to a patch of a lower hierarchical level) is at the same or upper LOD level in operation 106, the number of the triangular patches having the lower level among the adjacent triangular patches to the selected triangular patch (i.e., the number of patches of the lower hierarchical level) is determined in operation 108.
If it is determined that the number of the patches of the lower hierarchical level is 3 in operation 109, as described in
If it is determined that the number of the patches of the lower hierarchical level adjacent to the selected triangular patch of the upper hierarchical level is 2 in operation 111, in operation 112, as described in FIGS. 7(b) to 7(d), vertices of the unit triangular patches within the triangular patches of the lower hierarchical level, which are disposed in the boundaries between the triangular patches of the lower hierarchical level and the triangular patches of the selected upper hierarchical level, are connected consecutively with each other in a zigzag pattern.
If the number of the patches of the lower hierarchical level adjacent to the selected triangular patch of the upper hierarchical level is 1, as described in FIGS. 7(e) to (g), all vertices of the unit triangular patches of the triangular patches within the lower hierarchical level disposed in the boundaries between the triangular patches of the lower hierarchical level and the triangular patches of the upper hierarchical level are connected with vertices of the triangular patches of the upper hierarchical level facing to the boundary line, and as a result, the hierarchical mesh according to the present embodiment can be obtained.
The above described method for representing three-dimensional images with a multi-level LOD using the multi-level LOD hierarchical mesh can be implemented as computer readable codes in a computer readable recording medium. The computer readable recording medium includes various types of recording medium into which data can be read by a computer system are stored. Examples of the computer readable recording medium are ROM, RAM, CD-ROM, magnetic tapes, floppy disks, and optical data storing devices. Also, the computer readable recording medium can include one realized in the form of a carrier wave such as transmission through Internet. Also, codes which can be read by the computer based on a distribution mode are stored into the computer readable recording medium distributed within a computer system connected via a network and can also be executed.
According to the exemplary embodiments of the present invention, the multi-level LOD hierarchical mesh is configured using the triangular patches. Particularly, a mesh of a target image such as terrain is configured using information on height allocated to each vertex of the triangular patches included in the hierarchical mesh, and thus, usage of memory resources of a computer system can be reduced by approximately 3-fold.
Also, different from the conventional PM based method of dynamically generating vertices of the mesh, the multi-level LOD hierarchical mesh is configured in advance, and pieces of information on indices of vertices of the triangular patches for the hierarchical mesh are arranged separately. As a result, patches with various LOD levels can be produced and represented in real time.
In addition to the precedent configuration of the multi-level LOD hierarchical mesh and determination of the LOD of each patch using the index information for the vertices of the triangular patches used in the multi-level LOD hierarchical mesh configuration, connecting the triangular patches with different LOD levels without gaps can reduce usage of computation resources used for merging or separating the triangular patches.
It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2004-0107657 | Dec 2004 | KR | national |
| 10-2005-0061731 | Jul 2005 | KR | national |
