Hi Even, that is excellent, thank you. I have one question about the resampling workaround:
On Wed, 20 May 2015 at 19:34 Even Rouault <[email protected]> wrote: > Mike, > > > > > By my reading of https://trac.osgeo.org/gdal/wiki/rfc4_geolocate that > means > > the Geolocation tag from gdalinfo should have a PIXEL_STEP and LINE_STEP > of > > 5, and if I do this I get a much better result but it's still not right. > > I've just committed a patch in trunk that should put more sensible values > for > those values : > r29212 "HDF4: ProcessModisSDSGeolocation(): set more correct values for > PIXEL_/LINE_ OFFSET/STEP by comparing longitude and latitude subdatasets > dimensions with main subdataset dimensions" > > > > I've put a jpeg image of the result, with the coastline mapped and not > > lining up, here: > > > > http://staff.acecrc.org.au/~mdsumner/mod1.jpg > > Either the data itself is wrong, either there's an issue with the > geolocation > transformer... Later hypothesis is the more likely, although I've managed > to > make it work with L1B datasets where the tps or geoloc transformers gave > roughly the same results. > > I've gotten smoother results by resizing the longitude&latitude > subdatasets to > the main subdataset dimension > > gdal_translate > HDF4_SDS:UNKNOWN:"MOD021KM.A2012062.0455.006.2014220083128.hdf":1 > longitude.tif -outsize 1354 2030 -r cubic > > gdal_translate > HDF4_SDS:UNKNOWN:"MOD021KM.A2012062.0455.006.2014220083128.hdf":0 > latitude.tif > -outsize 1354 2030 -r cubic > > and then referencing them in the VRT produced with > > gdal_translate -of VRT > HDF4_SDS:UNKNOWN:"MOD021KM.A2012062.0455.006.2014220083128.hdf":2 data.vrt > > (and then by correcting the offset and step values to 0 and 1 respectively) > > Is this what occurs when warping generally? Or, even with your fix for PIXEL/LINE STEP/OFFSET is present will it still be better to do these external steps to improve the result? Thanks again, I've really learnt a lot through this process. Cheers, Mike. > You might want to do the warp with -wo SAMPLE_GRID=YES -wo SAMPLE_STEPS=100 > too > > But overall the reprojected image stays roughly at the same location. This > helps only removing a few artifacts on the edges. > > Even > > -- > Spatialys - Geospatial professional services > http://www.spatialys.com >
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