Visualisation

1. Visualisation By M. Varshosaz

2. Introduction • Graphical rendering of DTMs and derived information. • Very important for perceptual understanding and appreciation of DTMS. • Visualization addresses two objectives: • Interactive visualization for exploring, calibration and refinement applications. • Static visualization for basic communication of results. • Visualization tools include 3-D modeling, realistic scene rendering and animation.

3. Methods Based on Interactivity • Interactive • To explore models and refine • E.g. Flythrough • Static • To communicate results and concepts • E.g. contour and slope maps

4. static 2D space • Contour lines • Hill_ shading • Hypsometric tints • Combination with 2D data • Orthographic DTM representation visualization Dynamic (3D perspective) • Block diagrams • Panoramicviews 3D model (real 3D) 3D space Relief physical Model DTMs application representation -slope -aspect -profile curvature -planar curvature

5. Contour Lines • simple contour • simplest way • same contours interval • angle of view is perpendicular to the surface • assume land continuous • assume simplest gradient • bound to be erroneous • most metrical method • suited to measurement • does not dominate map • less reliant on manual skill

6. Contour Types • Indexed • Inclined • Shaded • Hachured • Combined with other visualisations

7. Index contours • Every 4th or 5th line - thicker • Labeled • Visual reinforcement

8. Index contours

9. Inclined Contour • Inclined view • Different contour interval • Better 3d view in mind

10. Shaded Contours • Black and White • Colored (pesudo coloring) • Continious • Stepped If 10<g(x,y)<30 then g(i,j)=15 If 30<g(x,y)<60 then g(i,j)=45 ,…

11. Contours: Discussion • High precision • Difficult to visualize • 3D impression only for experienced users • Requires map user to be experiencedoften used in combination with coloured fills of areas in between

12. Contours Combined With Tints • Specially for small scale maps, with generalised contours • Using “natural-looking” colours

13. Hachured Contours • light source assumed to be vertical in most cases • lines along direction of slope • width and/or spacing relate to steepness

14. Hachured Contours: Advantages • detailed slope change shown • suited to engraving • convenient for field sketches • supplement to contouring

15. Hachured Contours: Disadvantages • manual skill dependent • series maps lack uniformity • detail obscured • difficult to automate • no absolute height variation provided

16. Hill Shading • Dark areas to give shadow effects: natural impression of volumes • Direction of light normally from upper–left • Slope shaded in proportion to intensity of slope • Assumes artificial or imaginary light source • Development of air brush and printing important during 19th century • Smooth tonal variation possible

17. Hill Shading Factors • Sun azimuth: the direction of the incoming light, • ranging from 0ْ to 360ْ degree in a clockwise direction. • Sun’s altitude: The angle of the incoming sunlight measured above the horizon between 0ْ to 90ْ . • Surface slope: ranges from 0ْ to 90ْ . • Surface aspect: ranges from 0ْ to 360ْ.

18. Hill Shading • Diffuse Reflection Diffuse reflection assigns each pixel a gray value proportional to the cosine of the angle between the surface normal and the light vector. - easy -fast -more accurately for flatter and lowlands • Aspect Based Shading basing the shading on aspect Aspect-based shading is suited for mountainous areas • α = angle between aspect and the azimuth of the light direction

19. Hill Shading: Properties • No precision • Very good impression • Can be effectively combined with layer tinting and other information

20. Layer tinting (hypsometric tints) • Used gradient tints to depict elevation zones from lowlands to highlands • lighter values at higher elevations (warm yellows and reds ) • darker values at lower elevations (Blue and green ) • -stepped interval • continuous interval

21. Layer tinting - grey scale

22. Layer Tinting: Advantages • - Easily visualised • - Attractive • - Colour association can be used

23. Layer Tinting: Problems • Evenly balanced/perceptively different • All map elements affected • Colours for lowland must not affect detail • Avoid abrupt changes in colour (lose continuous surface) • May not match physiographic regions • Colour association

24. Combination with 2D data • Thematic map • Draped Images

25. 3D perspective 3D view parameters • Viewing azimuth • Viewing angle • Viewing distance • Z-scale (exaggeration factor) perspective model is made by overlapping of : 1-3D data (DTM) 2-camera model 3-Texture/material model 4-Illumination/shading model

26. 3D perspective • Block diagrams • similar to photographic systems • Suit for look realistic • not useful for recording exact shape • not useful for measurements of the objects • Panoramic views • less realistic view • used for exact measurements

27. Digital oblique views: construction (1) 3D data DTM+camera/standpoint info

28. Digital oblique views: construction (2) Perspective view 3D Data+hidden line/surface removal

29. Digital oblique views: construction (3) 3D data perspective view +Illumination/shading model

30. Digital oblique views: construction (4) Textured model 3D model+texture/material model

31. Oblique views: digital techniques

32. 3D View With Maps

33. Digital oblique views: elements Texture/materialmodel 3D data (eg. a DTM) Camera model “scene” Illumination/shading model