Improving the Representation of Major Landforms in Analytical Relief Shading

Improving the Representation of Major Landforms in Analytical Relief Shading

Brooke Marston
Bernhard Jenny
Oregon State University
#nacis2015

Bbaf1d0def6e102c6defedbb84537a2f?s=128

Nathaniel V. KELSO

October 16, 2015
Tweet

Transcript

  1. Improving the Representation of Major Landforms in Analytical Relief Shading

    Brooke Marston Bernhard Jenny NACIS Minneapolis October 14–17, 2015
  2. Relief Shading Analytical Manual Source: shadedreliefarchive.com

  3. Adjustment to Illumination Direction Global Local

  4. Why is manual preferred? • Locally bright and dark slopes improve

    legibility • Easier and faster to interpret topography • Better for small-scale maps where contours degenerate Source: shadedreliefarchive.com
  5. Why aren`t there more manually

  6. Benefits of Automation • Faster production of shaded relief adhering to

    manual design principles • More aesthetically pleasing maps • Explicit terrain visualization • Improve quality of maps produced by non-professionals
  7. Source: Orzan, A., et al., 2008. Diffusion Curves: A Vector

    Representation for Smooth-Shaded Images. ACM Transactions on Graphics (Proceedings of SIGGRAPH 2008), 27, Article 92:1–8. Diffusion Curves • Introduced by Orzan et al., 2008 • Create images with smooth color gradients using cubic Bézier splines with control points • Colors diffused independently on left and right sides of curves by linear interpolation
  8. Ridgelines Valley lines Diffusion curve shading

  9. Identifying valley lines

  10. Identifying ridgelines

  11. Terrain Tilting •  Wedge-shaped base with artificial elevation grade (γ)

    applied to terrain model 8 times (N, E, S, W, NE, NW, SE, SW) •  Ridgelines are filtered based on their stability
  12. Extracting Skeletal Lines Flow accumulation Maximum branch length Ridgeline and

    valley line vectors
  13. Illumination Adjustment

  14. Illumination Adjustment

  15. Aspect Simplification • Reduces variability of adjusted illumination directions • Results in

    more regular gray values along ridges and valleys Original Low tolerance High tolerance
  16. Diffusion Curve Shading

  17. Valley Floor Mask • Detected using seed fill algorithm • Visually connects

    adjacent mountain slopes Seed points Valley floor
  18. Standard analytical shading Diffusion Relief Shading Diffusion curve shading Valley

    floor mask + +
  19. Study Sites 1.  Alpine terrain 2.  Pre-alpine terrain 3.  Terrain

    with complex drainage network
  20. 1. Alpine Terrain Analytical Diffusion relief shading DEM Source: Federal

    Office of Topography swisstopo
  21. 1. Alpine Terrain Manual Diffusion relief shading DEM Source: Federal

    Office of Topography swisstopo
  22. 2. Pre-alpine Terrain Analytical Diffusion relief shading DEM Source: Federal

    Office of Topography swisstopo
  23. 3. Complex Drainage Network Analytical Diffusion relief shading DEM Source:

    USGS
  24. Limitations • Runtime • Spatial extent of terrain model • Unwanted artifacts in

    valley floor mask
  25. Conclusions • Diffusion curve shading enhanced analytical shading • Best results in

    terrain with sharp, clearly defined ridges and valleys • Tilting removes irrelevant or visually disturbing ridgelines • Our method presents alternative to other filter-based generalization approaches
  26. Future Work • Incorporate colors modulated by elevation and exposure to

    illumination (Jenny and Hurni 2006) • Integrate software applications
  27. Acknowledgments •  Tom Patterson, National Park Service •  OSU Cartography

    and Geovisualization Group •  Oregon State University, AAG Cartography Specialty Group, Google, ICA Commission on Mountain Cartography, Phi Beta Kappa
  28. Thank you Questions?

  29. Gray value = 255 × cos(α) Analytical Relief Shading Lambert

    Shading Algorithm
  30. Why is manual preferred? • Locally bright and dark slopes improve

    legibility and aesthetic quality • Easier and faster for the user to interpret topography • Better for small-scale maps where contours degenerate Source: reliefshading.com, Google Maps
  31. Why is manual preferred? • Better for small-scale maps where contours

    degenerate Source: shadedreliefarchive.com
  32. Identifying ridgelines

  33. Methods

  34. Diffusion Relief Shading E. Imhof manual relief shading Reproduction using

    Diffusion Curves Source: library.ethz.ch
  35. Graph-based Network Analysis • Series of vertices connected by edges • Generalizes

    line geometry and filters out short, unimportant ridgelines (a) Identify shortest leaf edge (b) Remove edge (c) Remove degree- two vertex (d) Connect remaining edges
  36. Methods

  37. Number of overlaps between maximum branch length grids Terrain Tilting

    (N, S, E, W) 1 2 3 4
  38. Extracting Skeletal Lines 1. Grayscale 2. Binary and skeletonize 3.

    Tracing from branch points 4. Vectors
  39. Methods

  40. Illumination Adjustment (a) northeast (b) northwest (c) north-south Dst –

    β = 0 Dst – β = π/2 Dst Dst – β = 3π/4 Dst Dst Dst + Dmax Dst + D No adjustment
  41. Skeletal Line Simplification • Line simplification algorithm simplifies diffusion curve geometry

    Original Simplified
  42. Methods

  43. Methods

  44. Methods

  45. Methods

  46. Methods

  47. Methods