(I know this is not a very active list ... this is a bit of a test to see if it can come alive...)
Hi all, At the moment few real cliffs appear in the terrain as the drop in elevation is spread over the spacing of the elevation grid. For the SRTM-1 30 metre spacing, this would reduce in the worst case 30m vertical cliffs to about a 45 degree slope, and for SRTM-3, well, just go and have a look at the White Cliffs around Dover in the UK. Now, OSM have cliffs (lines labelled with 'natural=cliff') which could be incorporated into the terrain. My first idea was to use ogr-decode to include the cliffs as just another line string that is turned into narrow polygons (like streams), and then using a new 'cliff' classification in terragear these polygons could have elevations assigned to their nodes based on the closest elevation grid point at top or bottom of the cliff, effectively turning them from almost flat polygons to almost side-on polygons. Now there are a few little things to solve there, like generating polygons that consistently have first and second points at bottom and top respectively, and working out where the closest elevation grid point might be. What is quite exciting is that once that is done the now almost-vertical cliff polygons could be automatically assigned the 'rock' material, and then you could use the procedural rock textures in no doubt spectacular ways. And where a stream goes over a cliff, you could have a waterfall, which could be a whole new effect. However, what this relatively simple plan neglects is that any non-cliff feature nodes between the cliff edge and the grid elevation point would have elevations assigned by the original elevation interpolation routines, and would thus stick out above the landscape at the base of the cliff, or else be sunken below the top of the cliff. The only way I can see to fix this is for the cliff lines to be added into the Array class, so that they can be taken into account for elevation calculations. There may also be issues around the edges of tiles that I don't have much of a handle on, so may or may not be significant. Does anybody reading this have any feedback as to how realistic this plan is? Am I missing anything here? James.
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