GDALRasterSource reproject with only targetCRS

[echeipesh]

This is possibly an issue for clarification. When using GDALRasterSource and GDALWarpOptions my expectation is that only targetCRS would be required because that's how it works with gdalwarp. However, I find that indeed both sourceCRS and targetCRS are required.

Example (using geotrellis 3.0.0-SNAPSHOT and latest version of this lib):

scala> import geotrellis.raster.gdal._
import geotrellis.raster.gdal._

scala> val rs = new GDALRasterSource("/Users/eugene/tmp/ppp_prj_2019_DJI.tif")
rs: geotrellis.raster.gdal.GDALRasterSource = GDALRasterSource(/Users/eugene/tmp/ppp_prj_2019_DJI.tif,GDALWarpOptions(-of VRT -ovr AUTO))

scala> val rs = new GDALRasterSource("/Users/eugene/tmp/ppp_prj_2019_DJI.tif", GDALWarpOptions(targetCRS = Some(geotrellis.proj4.WebMercator)))
rs: geotrellis.raster.gdal.GDALRasterSource = GDALRasterSource(/Users/eugene/tmp/ppp_prj_2019_DJI.tif,GDALWarpOptions(-of VRT -ovr AUTO))

scala> val rs = new GDALRasterSource("/Users/eugene/tmp/ppp_prj_2019_DJI.tif", GDALWarpOptions(sourceCRS = Some(geotrellis.proj4.LatLng), targetCRS = Some(geotrellis.proj4.WebMercator)))
rs: geotrellis.raster.gdal.GDALRasterSource = GDALRasterSource(/Users/eugene/tmp/ppp_prj_2019_DJI.tif,GDALWarpOptions(-of VRT -s_srs +proj=longlat +datum=WGS84 +no_defs  -t_srs +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs  -ovr AUTO))

scrolling to the right we can see that options are identical between just opening the file and providing targetCRS.

I'm guessing this is for a reason, but I'm unclear on what the reason is. Also its a little counter-intuitive so I think its worth an issue. The intention here is to have a fully lazy reprojection because call to GDALRasterSource.reproject will query the underlying GDAL Dataset for the source CRS in order to set it in the options. This is specifically what I would like to avoid in a scenario I'm working on.

https://github.com/geotrellis/geotrellis-contrib/blob/c67e35765df420f9e94169463749c81d6bd60802/gdal/src/main/scala/geotrellis/contrib/vlm/gdal/GDALRasterSource.scala#L115-L116

[pomadchin]

Looks like an oversight / typo. It can also be the legacy from the experience of working with usual GDAL bindings, where derived warped datasets can loose some of the metadata.

https://github.com/geotrellis/geotrellis-contrib/blob/master/gdal/src/main/scala/geotrellis/contrib/vlm/gdal/GDALWarpOptions.scala#L171-L173

The logic should be changed to

(sourceCRS, targetCRS) match {
  case (Some(source), Some(target)) => if(source != target) List("-s_srs", source.toProj4String, "-t_srs", target.toProj4String)
     else Nil
  case (Some(source), _) => List("-s_srs", source.toProj4String)
  case (_, Some(target)) => List("-t_srs", target.toProj4String)
}

And if tests won't fail, it is a good enough fix and it alings with an intuitive logic.

[pomadchin]

Resolved here https://github.com/locationtech/geotrellis/pull/3053