UNIT 39 - THE TIN MODEL

UNIT 39 - THE TIN MODEL

Compiled with assistance from Thomas K. Poiker, Simon Fraser University

  • A. INTRODUCTION
  • B. HOW TO PICK POINTS
  • C. HOW TO TRIANGULATE A TIN
  • D. ALTERNATIVE METHODS OF CREATING TINS
  • E. STORING TINS
  • F. ALGORITHMS ON TINS
  • REFERENCES
  • DISCUSSION AND EXAM QUESTIONS
  • NOTES

    UNIT 39 - THE TIN MODEL

    Compiled with assistance from Thomas K. Poiker, Simon Fraser University

    A. INTRODUCTION

    The TIN model

    Creating TINs

    B. HOW TO PICK POINTS

    1. Fowler and Little algorithm

    2. VIP (Very Important Points) Algorithm

    3. Drop heuristic

    C. HOW TO TRIANGULATE A TIN

    1. Distance ordering

    2. Delaunay triangulation

    D. ALTERNATIVE METHODS OF CREATING TINS

    Break lines

    TINs from contours

    E. STORING TINS

    1. Triangle by triangle

    2. Points and their neighbors

    Comparison of the two structures

    F. ALGORITHMS ON TINS

    Slope and aspect

    Contouring

    Finding Drainage Networks

    REFERENCES

    Chen, Z., and J.A. Guevara, 1987. "Systematic selection of very important points (VIP) from digital terrain models for construction triangular irregular networks," Proceedings, AutoCarto 8, ASPRS/ACSM, Falls Church, VA, pp. 50-56. A description of ESRI's VIP approach to constructing a TIN.

    Fowler, R.J., and J.J. Little, 1979. "Automatic extraction of irregular network digital terrain models," Computer Graphics 13:199-207.

    Heller, M., 1986. "Triangulation and Interpolation of Surfaces," in R. Sieber and K. Brassel (eds), A Selected Bibliography on Spatial Data Handling: Data Structures, Generalization and Three-Dimensional Mapping, Geo- Processing Series, vol 6, Department of Geography, University of Zurich, pp 36 - 45. A good overview with literature, mainly on triangulation.

    Mark, D. M., 1975. "Computer Analysis of Topography: A Comparison of Terrain Storage Methods," Geografisker Annaler 57A:179-188. A quantitative comparison of regular grids and triangulated networks.

    Mark, D.M., 1979. "Phenomenon-Based Data-Structuring and Digital Terrain Modelling," Geo-Processing 1:27-36. A very interesting conceptual article proposing a phenomenon-based approach to data structuring. Such an approach has to involve expert knowledge of the phenomenon.

    Peucker, T.K., R.J. Fowler, J.J. Little and D.M. Mark, 1978. "The Triangulated Irregular Network," Proceedings, American Society of Photogrammetry: Digital Terrain Models (DTM) Symposium, St. Louis, Missouri, May 9-11,

    1978, pp 516-540. The basic description of the original TIN project.

    DISCUSSION AND EXAM QUESTIONS

    1. Argue the differences between the regular grid and the triangular net approaches. Apply the argument to the computation of slope, contouring and visibility.

    2. Mark's article in 1979 argued that the TIN model was more appropriate to the nature of certain geographical phenomena. Do you agree? For what types of landforms is TIN most and least appropriate?

    3. Discuss the various methods proposed for selecting TIN vertices from a DEM, and their relative strengths and weaknesses.

    4. Describe how information on directions of flow can be obtained from a TIN, and the nature of the extracted stream network. How does this compare to networks derived from DEMs?


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