Improving the Representation of Major Landforms in Analytical Relief Shading

Brooke Marston
Bernhard Jenny
Oregon State University
#nacis2015

Transcript

1. Improving the Representation of Major
   Landforms in Analytical Relief Shading
   Brooke Marston
   Bernhard Jenny
   NACIS Minneapolis
   October 14–17, 2015
   

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2. Relief Shading
   Analytical Manual
   Source: shadedreliefarchive.com
   

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3. Adjustment to Illumination Direction
   Global Local
   

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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
   

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5. Why aren`t there more manually

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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
   

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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
   

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8. Ridgelines Valley lines
   Diffusion curve shading
   

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9. Identifying valley lines

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10. Identifying ridgelines

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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
    

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12. Extracting Skeletal Lines
    Flow accumulation Maximum branch
    length
    Ridgeline and valley
    line vectors
    

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13. Illumination Adjustment

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14. Illumination Adjustment

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15. Aspect Simplification
    • Reduces variability of adjusted illumination directions
    • Results in more regular gray values along ridges and valleys
    Original
    Low
    tolerance
    High
    tolerance
    

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16. Diffusion Curve Shading
    

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17. Valley Floor Mask
    • Detected using seed fill algorithm
    • Visually connects adjacent mountain slopes
    Seed points Valley floor
    

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18. Standard analytical
    shading
    Diffusion Relief Shading
    Diffusion curve shading
    Valley floor mask
    + +
    

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19. Study Sites
    1.  Alpine terrain
    2.  Pre-alpine terrain
    3.  Terrain with complex drainage network
    

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20. 1. Alpine Terrain
    Analytical Diffusion relief shading
    DEM Source: Federal Office of Topography swisstopo
    

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

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

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23. 3. Complex Drainage Network
    Analytical Diffusion relief shading
    DEM Source: USGS
    

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24. Limitations
    • Runtime
    • Spatial extent of terrain model
    • Unwanted artifacts in valley floor mask
    

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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
    

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26. Future Work
    • Incorporate colors modulated by elevation and
    exposure to illumination (Jenny and Hurni 2006)
    • Integrate software applications
    

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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
    

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28. Thank you
    Questions?
    

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

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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
    

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31. Why is manual preferred?
    • Better for small-scale maps where contours degenerate
    Source: shadedreliefarchive.com
    

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32. Identifying ridgelines

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33. Methods
    

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34. Diffusion Relief Shading
    E. Imhof manual relief
    shading
    Reproduction using Diffusion
    Curves
    Source: library.ethz.ch
    

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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
    

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36. Methods
    

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37. Number of overlaps
    between maximum
    branch length grids
    Terrain Tilting (N, S, E, W)
    1
    2
    3
    4
    

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38. Extracting Skeletal Lines
    1. Grayscale 2. Binary and skeletonize
    3. Tracing from branch points 4. Vectors
    

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39. Methods
    

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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
    

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41. Skeletal Line Simplification
    • Line simplification algorithm simplifies diffusion curve
    geometry
    Original Simplified
    

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42. Methods
    

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43. Methods
    

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44. Methods
    

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45. Methods
    

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46. Methods
    

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47. Methods
    

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