一种基于屏幕的三维地图线状符号渲染方法
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摘要
作为地理信息系统中的重要组成部分,矢量数据在三维GIS中发挥着重要作用,如指示地理对象、解释空间关系和丰富图面信息等。随着图形硬件的迅速发展和虚拟地理环境的广泛应用,为了在三维地图中精确、高效地绘制出具有复杂样式的线性地图符号,本文提出了一种利用Open GL Shader Language的三维地形表面线状符号渲染方法。该方法通过对矢量数据进行编码形成纹理数据,完成矢量数据在程序与GPU间的传输;将地形单元和矢量线段间的映射关系存储在索引纹理中,用于关联线段的实时查找;通过计算当前屏幕片元与关联矢量线段的空间位置关系,判断片元所属符号的区域,进而设置片元的颜色。实验表明,本方法可在三维地形上高质量地渲染出几种典型的复杂线状符号,并能保持较好的渲染性能。
Vector data, as an important part of Geographic Information System(GIS), plays a significant role in three-dimensional(3D) GIS to indicate geographic objects, explain spatial relationships and enrich map information. However, in the study of 2 D vector rendering onto 3D terrain surface, vector lines drawn by traditional algorithms are relatively simple and monotonous, mainly shown as monochromatic lines or multicolor parallel lines, which cannot meet the growing demands for visualization. With the rapid development of graphics hardware acceleration and the widespread application of Virtual Geographical Environment(VGE), in order to draw the complicated linear map symbol in 3D map effectively and efficiently, this paper proposes a screenbased method that renders the linear symbol onto the 3D terrain surface with the use of Open GL Shader Language(GLSL). We transfer the vector data from the procedure to Graphics Processing Unit(GPU) by encoding the vector data into the texture data. The mapping relationships between terrain units and vector lines are stored in the index texture, and the mapping is used for looking up the related line segments in real-time. In addition, the node texture stores the attribute of vector lines. We calculate the position relationship between screen fragments and related line segments, and find out the area where the current fragment belongs to. If the current screen fragment has associated line segments, then we get the attributes of the related line segments from the node texture and set the fragment color. It is worth mentioning that we provide a variety of symbolic functions, which can render different types of vector line segments, including gradient lines, periodic lines, etc.In order to achieve better visual effects, we apply a series of detail optimization operations to related line segments, including anti-aliasing and corner optimization. Finally, we take the Purple Mountain as an example and render vector lines onto it using the proposed method. The experiments demonstrated that vector lines rendered by our method show great visual effect and our method can render some complicated and typical line symbols with high performance while keeping rendering efficiency at real time level.
Vector data, as an important part of Geographic Information System(GIS), plays a significant role in three-dimensional(3D) GIS to indicate geographic objects, explain spatial relationships and enrich map information. However, in the study of 2 D vector rendering onto 3D terrain surface, vector lines drawn by traditional algorithms are relatively simple and monotonous, mainly shown as monochromatic lines or multicolor parallel lines, which cannot meet the growing demands for visualization. With the rapid development of graphics hardware acceleration and the widespread application of Virtual Geographical Environment(VGE), in order to draw the complicated linear map symbol in 3D map effectively and efficiently, this paper proposes a screenbased method that renders the linear symbol onto the 3D terrain surface with the use of Open GL Shader Language(GLSL). We transfer the vector data from the procedure to Graphics Processing Unit(GPU) by encoding the vector data into the texture data. The mapping relationships between terrain units and vector lines are stored in the index texture, and the mapping is used for looking up the related line segments in real-time. In addition, the node texture stores the attribute of vector lines. We calculate the position relationship between screen fragments and related line segments, and find out the area where the current fragment belongs to. If the current screen fragment has associated line segments, then we get the attributes of the related line segments from the node texture and set the fragment color. It is worth mentioning that we provide a variety of symbolic functions, which can render different types of vector line segments, including gradient lines, periodic lines, etc.In order to achieve better visual effects, we apply a series of detail optimization operations to related line segments, including anti-aliasing and corner optimization. Finally, we take the Purple Mountain as an example and render vector lines onto it using the proposed method. The experiments demonstrated that vector lines rendered by our method show great visual effect and our method can render some complicated and typical line symbols with high performance while keeping rendering efficiency at real time level.
引文
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[16]Agrawal A,Radhakrishna M,Joshi R C.Geometry-based mapping and rendering of vector data over LOD phototextured 3D terrain models[C].Proceedings of the 14th International Conference in Central Europe on Computer Graphics.WSCG,2006:1-8.
[17]Schneider M,Klein R.Efficient and accurate rendering of vector data on virtual landscapes[J].Journal of WSCG,2007,15(15):1-3.
[18]刘昭华,杨靖宇,戴晨光.基于模板阴影体算法的矢量数据在三维场景中的绘制[J].测绘工程,2009,18(1):38-41.[Liu S H,Yang J Y,Dai C G.Rendering vector data over 3D terrain based on stencil shadow volume algorithm[J].Engineering of Surveying and Mapping,2009,18(1):38-41.]
[19]曹雪峰,万刚,李锋,等.模板阴影体扩展方法[J].中国图象图形学报,2013,18(4):81-86.[Cao X F,Wan G,Li F,et al.Extension method of stencil shadow volume[J].Journal of Image and Graphics,2013,18(4):81-86.]
[20]She J F,Zhou Y,Tan X,et al.A parallelized screen-based method for rendering polylines and polygons on terrain surfaces[J].Computers&Geosciences,2017,99(2):19-27.
[21]Yang L,Zhang L Q,Kang Z Z,et al.An efficient rendering method for large vector data on large terrain models[J].Science China(Information Sciences),2010,53(6):1122-1129.
[22]Yang L,Zhang L Q,Ma J T,et al.Efficient simplification of large vector maps rendered onto 3D landscapes[J].IEEE Computer Graphics&Applications,2011,31(2):14-23.
[23]Vaaraniemi M,Treib M,Westermann R.High-quality cartographic roads on high-resolution DEMs[J].Journal of Wscg,2013,19:41-48.
[24]谈心,佘江峰.二维矢量线符号在三维地形表面的贴合渲染方法[J].地球信息科学学报,2015,17(12):1483-1489.[Tan X,She J F.A new method of rendering 2D vector line symbols on 3D terrain surface[J].Journal of Geo-information Science,2015,17(12):1483-1489.]
[2]陈鸿,汤晓安,谢耀华,等.基于视点相关透视纹理的矢量数据在三维地形上的叠加绘制[J].计算机辅助设计与图形学学报,2010,22(5):753-761.[Chen H,Tang X A,Xie Y H,et al.Rendering vector data over 3D terrain with view-dependent perspective texture mapping[J].Journal of Computer-Aided Design&Computer Graphics,2010,22(5):753-761.]
[3]Qiao Z,Weng J,Sui Z,et al.A rapid visualization method of vector data over 3D terrain[C].International Conference on Geoinformatics.IEEE,2011:1-5.
[4]朱庆.三维GIS及其在智慧城市中的应用[J].地球信息科学学报,2014,16(2):151-157.[Zhu Q.Full three-dimensional GIS and its key roles in smart city[J].Journal of Geo-information Science,2014,16(2):151-157.]
[5]Schneider M,Guthe M,Klein R.Real-time rendering of complex vector data on 3D terrain models[C].Proceedings of the 11thInternational Conference on Virtual Systems and Multimedia.IEEE,2005:573-528.
[6]Kersting O,Dollner J.Interactive 3D visualization of vector data in GIS[C].Proceedings of the 10thACM International Symposium on Advances in Geographic Information Systems.ACM,2002:107-112.
[7]Zhu J,Zhang A L,Yin L Z,et al.3D GIS modeling of virtual high-speed railway scene based on Arc Globe[C]//In Proceedings of the 7thInternational Conference on Image and Graphics.IEEE,2013:811-815.
[8]Liang J M,Gong J H,Li W H,et al.A visualization-oriented 3D method for efficient computation of urban solar radiation based on 3D-2D surface mapping[J].International Journal of Geographical Information Science,2014,28(4):780-798.
[9]Lin T P,Lin H,Hu M Y.Three-dimensional visibility analysis and visual quality computation for urban open spaces aided by Google Sketch Up and Web GIS[J].Environment&Planning B,2017,44(4):618-646.
[10]Yue S S,Yang J S,Chen M,et al.A function-based linear map symbol building and rendering method using shader language[J].International Journal of Geographical Information Science,2016,30(2):143-167.
[11]Wu M G,Zheng P B,Lu G N,et al.Chain-based polyline tessellation algorithm for cartographic rendering[J].Cartography&Geographic Information Science,2016,44(6):491-506.
[12]窦世卿,赵学胜,刘成军,等.河网线要素与DEM综合的三维Douglas-Peucker算法[J].测绘学报,2016,45(4):450-457.[Dou S Q,Zhao X S,Liu C J,et al.The three dimensional Douglas-Peucker algorithm for generalization between river network line element and DEM[J].Acta Geodaetica et Cartographica Sinica,2016,45(4):450-457.]
[13]Li G S,Bordoloi U D,Shen H W.Chameleon:An interactive texture-based rendering framework for visualizing three-dimensional vector fields[C]//Proceedings of IEEE Visualization.IEEE,2003:241-248.
[14]Taibo J,Jaspe A,Seoane A,et al.Practical line rasterization for multi-resolution textures[C].Smart TOOLS and Apps for Graphics.Eurographics Association,2014:9-18.
[15]Wartell Z,Kang E,Wasilewski T,et al.Rendering vector data over global,multi-resolution 3D terrain[C].Proceedings of the Symposium on Data Visualization.Eurographics Association,2003:213-222.
[16]Agrawal A,Radhakrishna M,Joshi R C.Geometry-based mapping and rendering of vector data over LOD phototextured 3D terrain models[C].Proceedings of the 14th International Conference in Central Europe on Computer Graphics.WSCG,2006:1-8.
[17]Schneider M,Klein R.Efficient and accurate rendering of vector data on virtual landscapes[J].Journal of WSCG,2007,15(15):1-3.
[18]刘昭华,杨靖宇,戴晨光.基于模板阴影体算法的矢量数据在三维场景中的绘制[J].测绘工程,2009,18(1):38-41.[Liu S H,Yang J Y,Dai C G.Rendering vector data over 3D terrain based on stencil shadow volume algorithm[J].Engineering of Surveying and Mapping,2009,18(1):38-41.]
[19]曹雪峰,万刚,李锋,等.模板阴影体扩展方法[J].中国图象图形学报,2013,18(4):81-86.[Cao X F,Wan G,Li F,et al.Extension method of stencil shadow volume[J].Journal of Image and Graphics,2013,18(4):81-86.]
[20]She J F,Zhou Y,Tan X,et al.A parallelized screen-based method for rendering polylines and polygons on terrain surfaces[J].Computers&Geosciences,2017,99(2):19-27.
[21]Yang L,Zhang L Q,Kang Z Z,et al.An efficient rendering method for large vector data on large terrain models[J].Science China(Information Sciences),2010,53(6):1122-1129.
[22]Yang L,Zhang L Q,Ma J T,et al.Efficient simplification of large vector maps rendered onto 3D landscapes[J].IEEE Computer Graphics&Applications,2011,31(2):14-23.
[23]Vaaraniemi M,Treib M,Westermann R.High-quality cartographic roads on high-resolution DEMs[J].Journal of Wscg,2013,19:41-48.
[24]谈心,佘江峰.二维矢量线符号在三维地形表面的贴合渲染方法[J].地球信息科学学报,2015,17(12):1483-1489.[Tan X,She J F.A new method of rendering 2D vector line symbols on 3D terrain surface[J].Journal of Geo-information Science,2015,17(12):1483-1489.]
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