Cropping GeoTIFF to square at specific lat/long for use as Unity 3d terrain heightmap?

Question

I have some GeoTIFF files that contain elevation data. I have an area defined by latitude and longitude, and I would like to extract the elevation as a heightmap from the GeoTIFF files to use in Unity. Unity requires the heightmap to be both square and the dimensions to be 2^n + 1. The terrain is represented in Unity as a literal square mesh in x[0-2159.9], z[0-2159.9] with elevation in y dimension.

I've been able to import my files into QGIS 3.6 without any trouble and they all line up as expected (NOAA source and SRTM). I've even been able to use gdal_translate to convert to a raw heightmap (ENVI). What I'm struggling with is how to define a square region in QGIS (I can't even figure out how to add a layer that will let me add arbitrary shapes, let alone how to figure the dimensions of that shape). I can't just do delta latitude = delta longitude because that's really a parallelogram, or at least I assume it is.

UPDATE: to simplify things, I have updated the region of interest to be a square, and the lat/long is now:

• NE: -82.67761,28.00410
• SW: -82.69958,27.98470

Ultimately, what I'm trying to do is create a terrain in Unity that matches up exactly to the transformations that Mapbox does (the source of my coordinates is the the coordinates of the Mapbox tiles) so that I can map points of interest from Mapbox onto my terrain in the correct locations.

Answer 1

I was able to solve this with the help of https://stackoverflow.com/questions/32112597/how-to-crop-polygon-with-latitude-and-longitude-coordinates-from-geotiff-image-i. Ultimately I used the following gdal command line utilities:

1. Create crop shape GeoJson file. I used Mapbox Studio to create my GeoJson. I could have done it by hand, but Mapbox allowed me to verify I had done it correctly:
   • { "geometry": { "coordinates": [ [ [-82.69958, 28.0041], [-82.67761, 28.0041], [-82.67761, 27.9847], [-82.69958, 27.9847], [-82.69958, 28.0041] ] ], "type": "Polygon" }, "type": "Feature", "properties": {} }
2. Crop to area of interest:
   • gdalwarp -of GTiff -crop_to_cutline -cutline SafetyHarborGeoExplorerBoundary.json Job472561_NOAA_SLR_DEM.tif heightmap.tif
3. Get statistics to extract min and max height to input into Unity:
   • gdalinfo -mm heightmap.tif
4. Convert to raw file for Unity:
   • gdal_translate heightmap.tif heightmap.raw –ot UInt16 –scale –of ENVI –outsize 2049 2049
5. depending on size/location of original data, might need to do some edits in a paint program to make the final file actually square

The coordinate system doesn't enter into it. That is implicitly defined by the mapping that created the mesh target in my modeling program. Since I already had the model coordinates for each corner and their respective mapping to lat/long, it is a simple linear interpolation from the raster data to the model.