1mjb -- May 9, 2013Oregon State UniversityComputer GraphicsTerrain VisualizationMike [email protected] State Universitymjb -- May 9, 2013Oregon State UniversityComputer GraphicsReminder: Color Scale Transfer FunctionsThe biggest rule here is to design something that is intuitive. The “snapshot rule” definitely applies!Sometimes elevation is represented by a color transfer function, like one of these. Sometimes elevation is represented by the color of what exists at that elevation (sand, dirt, grass, trees, snow, etc.) Remember Tufte’s Do No Harm admonition.2mjb -- May 9, 2013Oregon State UniversityComputer GraphicsA Possible Color Scale Transfer Function for OregonAssume snow level is at 1.5 milesSculpting the transfer function in HSV.Full value, no saturation above 1.5 miles, full-saturation hue change below 1.5 miles.mjb -- May 9, 2013Oregon State UniversityComputer GraphicsHeight ExaggerationMost terrain visualization applications require height exaggeration to see any elevation changes. Why? Consider Oregon for example. Oregon is about 360 x 260 miles horizontally, and has an elevation range of about 2.5 miles vertically. This makes the elevation range less than 1% of the horizontal dimensions – hardly noticeable. However, be careful of going overboard.Height Exaggeration = 1.0Height Exaggeration = 3.0Height Exaggeration = 2.0Height Exaggeration = 10.03mjb -- May 9, 2013Oregon State UniversityComputer GraphicsS* = 0 miles S* = 0.17 milesS* = 1.00 miles S* = 2.00 milesDifferent Contour Linesmjb -- May 9, 2013Oregon State UniversityComputer GraphicsMultiple Contour Lines4mjb -- May 9, 2013Oregon State UniversityComputer GraphicsLightingABCˆnˆAB ACnAB AC×=×To do effective lighting of terrain surfaces, you need a surface normal for each triangle. You can get this with the cross product and unitizing:You can use this unitized normal directly in the OpenGL glNormal3f( ) call to do dynamic OpenGL lighting.You can also do pseudo-lighting, where you assume that the sun is in a fixed direction from the scene. The diffuse portion of the lighting model is then:ˆˆdI n L=iˆnˆLIf you assume that the sun is directly overhead, then this reduces to just the vertical component of the unit surface normal.mjb -- May 9, 2013Oregon State UniversityComputer GraphicsLighting Height ExaggerationAt times it is helpful to exaggerate the height for the lighting computations, but not for the height display. This ends up exaggerating the lighting effects, which is usually a good thing.Lighting Height Exaggeration = 1.0Lighting Height Exaggeration = 10.0Lighting Height Exaggeration = 5.0Lighting Height Exaggeration = 20.05mjb -- May 9, 2013Oregon State UniversityComputer Graphicss = 1.0s = 0.0t = 0.0t = 1.0x=xminx=xmaxy=yminy=ymaxminmax min0.1. 0.x xsx x−−=− −minmax min0.1. 0.y yty y−−=− −minmax minx xsx x−=−minmax miny yty y−=−(x,y)(s,t)Computing (s,t) Texture Coordinates from Longitude (x) and Latitude (y)mjb -- May 9, 2013Oregon State UniversityComputer Graphicss = 1.0s = 0.0t = 0.0t = 1.0Computing (s,t) Texture Coordinates:What if the Texture doesn’t occupy the entire Image?t = tmaxx=xmaxy=yminy=ymax(x,y)(s,t)minmax min0.1. 0.x xsx x−−=− −minmax max min0.0.y ytt y y−−=− −minmax minx xsx x−=−max minmax min( )t y yty y−=−6mjb -- May 9, 2013Oregon State UniversityComputer GraphicsNo texturingGL_REPLACEUnderlying lighting withGL_MODULATEOpenGL Texture Environmentsmjb -- May 9, 2013Oregon State UniversityComputer GraphicsUSGS National Elevation Database ProgramContinental US Data available free at 10m resolution.Mt. HoodMt. HoodSalemhttp://ned.usgs.gov/7mjb -- May 9, 2013Oregon State UniversityComputer GraphicsNo ExaggerationExaggeratedTerrain Height Bump-mapping:Don’t Actually Supply the Geometry, Just Manipulate the Normalsmjb -- May 9, 2013Oregon State UniversityComputer GraphicsTerrain Height Bump-mapping: Coloring by Height8mjb -- May 9, 2013Oregon State UniversityComputer GraphicsNo ExaggerationExaggeratedTerrain Height Bump-mapping: Coloring by Heightmjb -- May 9, 2013Oregon State UniversityComputer GraphicsCorvallisTerrain Height Bump-mapping: Zooming InSalemPortlandEugene9mjb -- May 9, 2013Oregon State UniversityComputer GraphicsTerrain Height Bump-mapping: Zooming InCrater Lakemjb -- May 9, 2013Oregon State UniversityComputer Graphicshttp://egsc.usgs.gov/isb/pubs/MapProjections/projections.htmlMap ProjectionsMercatorTransverseMercator10mjb -- May 9, 2013Oregon State UniversityComputer Graphicshttp://egsc.usgs.gov/isb/pubs/MapProjections/projections.htmlMap ProjectionsMillerCylindricalRobinsonmjb -- May 9, 2013Oregon State UniversityComputer Graphicshttp://egsc.usgs.gov/isb/pubs/MapProjections/projections.htmlMap ProjectionsSinusoidal Equal AreaOrthographic11mjb -- May 9, 2013Oregon State UniversityComputer Graphicshttp://egsc.usgs.gov/isb/pubs/MapProjections/projections.htmlMap ProjectionsGnomonicAlbers Equal Area