“A terrain and cloud computer image generation model” by Dungan

  • ©William Dungan




    A terrain and cloud computer image generation model



    A method is presented that produces a realistic simulation of terrain using source data from the Defense Mapping Agency (DMA). Spatially compact objects are presently modeled with some success at realism. Because terrain is large in extent it exhibits special problems. These problems include: data base size and generation, masking priority, and shading. An array of height values can be created from the DMA terrain file. Height is a single valued function of the array coordinate pair. The pair has implicit positional information. A masking priority algorithm is used which has no restriction on observer geometry. The algorithm searches the height array along the line of sight for the first visible position in the array. This approach requires no clipping or depth sorting of surface representations. The height array indices are used to access the pixel shade from a registered, orthonormal texture array. The use of texture provides a simple way to add nonlinear shading for a realistic representation with flexible data base generation. Atmospheric attenuation is a method used to increase realism. Methods are in use which produce haze or fog with constant attenuation. The line-of-sight search is used to produce realistic clouds with spatially variable attenuation. Terrain and clouds are adequately simulated using this method of modeling. The data structures of height and texture arrays are simple, easily generated, and make good use of storage resources. Resolving masking priority along the line of sight is a visible surface algorithm which has advantages over hidden surface algorithms. Realistic representations such as texture and atmospheric attenuation are used with some success.


    1. Badler, N.I., and O’Rourke, J. A representation and display system for the human body and other three-dimensional curved objects. University of Pennsylvania, Department of Computer and Information Science, Technical Report (February 1977).
    2. Badler, N.I., and O’Rourke, J. Decomposition of three-dimensional objects into spheres. IEEE Pattern Recognition and Artificial Intelligence Workshop, Princeton, N.J. (1978).
    3. Badler, N., and Bajcsy, R. Three-dimensional representations for computer graphics and computer vision. Siggraph ’78 Proceedings, (August 1978), 153-160.
    4. Blinn, J.F. Simulation of wrinkled surfaces. Siggraph ’78 Proceedings, (August 1978), 286-292.
    5. Blinn, J.F., and Newell, M.E. Texture reflection in Computer Generated Images. CACM 19, 10 (October 1976) 542-547.
    6. Bunker, W., and Ingalls, M. Circles, texture, etc., alternate approaches to CIG scene detail. A Collection of Technical Papers, AIAA Flight Simulation Technologies Conference (September 1978), 49-58.
    7. Bunker, W., and Heartz, R. Perspective display simulation of terrain. Air Force Human Resources Laboratory, AFHRL-TR-76-39 (June 1976).
    8. Catmull, E. Computer display of curved surfaces. Proc. Conf. on Computer Graphics, Pattern Recognition, and Data Structure, (May 1975), 11-17.
    9. Defense Mapping Agency, Product specifications for digital landmass system (DLMS) data base. PS/ICD (EFG)/100, (July 1977).
    10. Dungan, W., Stenger, A., Sutty, G. Texture tile considerations for raster graphics. Siggraph ’78 Proceedings, 12, 3 (August 1978), 130-134.
    11. Faintich, M.B. Digital scene and image generation. Naval Weapons Laboratory Technical Report, TR-3147, (1974).
    12. Forrest, A.R. On Coons and other methods for representation of curved surfaces. Computer Graphics and Image Processing, 1, 4 (1972), 341-359.
    13. Gouraud, H. Continuous shading of curved surfaces. IEEE Transactions on Computers, 20,6 (June 1971), 623-629.
    14. Horn, B. Hill-shading and the reflectance map. Proceedings: Image Understanding Workshop. (April 1979), 79-120.
    15. Jancaitis, J.R. Modeling and contouring irregular surfaces subject to constraints. Army Engineer Topographic Laboratories. ETL-CR-74-19 (January 1975).
    16. Phong, B.T. Illumination for computer generated pictures. Graphics and Image Processing CACM 18, 6 (June 1975), 311-317.
    17. Watkins, G.S. A real-time visible surface algorithm. Department of Computer Science, University of Utah, UTEC-CSC-70-101 (June 1970).
    18. Williams, L. Casting curved shadows on curved surfaces. SIGGRAPH ’78 Proceedings (August 1978), 270-274.

ACM Digital Library Publication:

Overview Page: