I took a quick trip through this gdal tutorial on raster data, albeit with SRTM data instead of the example data. Things I learned:
- gdalinfo has useful flags for finding min/max values, stats, etc.
- gdal_translate is how you render a dataset to an image
gdal_translate -ot byte -scale 1152 3184 -of PNG N39W120.hgt test.png
Input range doesn’t seem to autoscale, despite what the docs say. Haven’t figured out how to apply a custom colormap yet. (The FAQ is discouraging, but gdaldem color-relief might do what I need.) The PNG output from GDAL doesn’t seem to have any geodata stored in PNG chunks.
- gdalwarp is how you reproject data
- gdal_merge is how you mosaic images. You can use gdalwarp to do it, too, but it’s overkill.
gdalwarp N39W120.hgt N39W121.hgt N38W120.hgt N38W121.hgt big.tiff
gdal_translate -outsize 50% 50% -scale 1000 3000 -of PNG big.tiff test.png
- gdal_rasterize lets you render vector data (via OGR) into raster data
- gdaladdo creates downsampled overviews for data, for faster access. In my previous experiments the overviews didn’t make mapserver any faster on my SRTM data.
- gdal has virtual formats which are a text file that describes multiple raster files as a single dataset. mapserver uses something different to accomplish this, a shapefile.