Van Der Grinten lattitude error beyond 180 degrees

[theconor]

Hello,

I type gdalwarp -t_srs "+proj=vandg" 15deg02grid.tif 15deg02vandggrid.tif The input file is a whole world TIFF (15degree raster grid, 5400 x 2700 pixels) and no compression.

The output TIFF has two errors. 1) The image (map) that goes beyond 180 degrees to fill the corners of this Van der Grinten tiff is incorrect in latitude, as evidenced by the abrupt change of the angle of the latitude lines.

2) A band of longitude (approx 175 degrees to 180 degrees west arc) is solid black where there should be projected image.

[theconor]

raster lat lon grid warped from geographic to V d Grinten

[warmerdam]

The black wedge is presumably because of a problem with identifying the valid edge. I think some of the warp options from:

​http://www.gdal.org/structGDALWarpOptions.html#08d1fa7a79849bd3735214a26e2a9722

may be helpful. For instance adding -wo SOURCE_EXTRA=100 to pull an extra 100 pixels around source windows.

It is not immediately clear to me why the discontinuity exists, but I presume this is some effect of the math "over the horizon", and that the taransformation from VDG back to lat/long is working in areas that aren't strictly speaking meaningful. Do you feel a strong need to have this aspect looked into? If so, I'd suggest trying some back and forth transformations with the PROJ.4 commandline programs to isolate what is likely going on, and then - if necessary - the issue could be taken up with Gerald Evenden (PROJ.4 author) if it is really a PROJ issue.

[warmerdam]

I don't think there is any outstanding issue, and there was no followup from the reporter.