Making Layers

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Revision as of 14:04, 9 June 2006 by (Talk)
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This is the beginning of an attempt to try to document a process so people that have GeoTIFF's can produce and maybe even serve up data for WorldWind. If you have any insights or info please add on.

Things We Know We Know

  1. WW's tiling scheme.
  2. Formula to go from Lat/Long to WW tile numbers.
  3. Nowak has a C program that uses GDAL to do this and he has another progam that packs them up so you dont have to manage zillions of files + a little PHP script to extract the correct tile from the image pyramid.
  4. News Flash! : Nowak released source code to DSTile (the Tiler) and TilePack (packs up tiles into a image pyramid so you dont have zillion of files) as Open Source (BSD licensed)
  1. What if you were to call dstile dynamically from inside WorldWind? Urobots talks about how to do this in his blog.
  2. Lucians OnEarth code for Apache to 'sniff' WorldWind requests, pass the request off to WMS (if needed) and cache the tiles if they are not already cached Download

Things We Know We Don't Know

  1. How does altitude relate to a level in a layer being displayed?
  2. How does <TileSize> and <Level0TileDegrees> affect #1?
  3. When do you know when to 'stop'? (ie. how do you know you are at 1:1)
  4. Even though L0TD == 2.25, how do we get larger tiles when viewing the whole earth?

Some answers came here

The Procedure for Making (As Far As I understand It Right Now)

  1. Obtain a georeferenced geotiff and reproject it to EPSG:4326. (or reproject with 'gdalwarp' in step 3 as you go along)(note: for those crusty-brained barnacle heads, ESPG:4326 = WGS84, and NAD83 is supposedly generally equivalent- check to verify before you take my word for it, though)
  2. Get the bounds of the GTiff.
  3. Take the lower left bounds and round to the nearest multiple of L0TD for lat and lon.
  4. Extract a L0TD sized chunk of the GeoTIFF starting at the coordinates of #3..
  5. Resample the chunk to <TileSize>(scale it to 512x512px or whatever tilesize you pick) and convert to image format of choice.
  6. Place it in the correct directory and rename the tile according to the naming formula. <insert naming formula here>
  7. Iterate in L0TD sized chunks over the entire TIFF till you have covered the upper and right side bounds.
  8. Divide L0TD by 2, and start over with #3
  9. Stop when you are at 1:1 scale (ie your L0TD sized chunk is less than <TileSize> in one of the dimensions.

TIFF viewers

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