The proj_factors(...) function, which a.o. returns the meridian convergence in the PJ_FACTORS typedef, may be useful in this work.
Den fre. 25. jun. 2021 kl. 12.26 skrev Even Rouault < even.roua...@spatialys.com>: > Michael, > > A general solution would have more appeal, although I suspect it will be a > bit more computation intensive as you'll probably have to transform to > invoke PROJ multiple times per grid point to compute the direction to the > North > > Even > Le 25/06/2021 à 06:29, Michael Sumner a écrit : > > Hello, we're using `gdaldem aspect` on polar grid products and we need to > convert the grid-oriented directions to compass oriented ones, > location-specific directions, where "compass north" is dependent on > longitude. > > It's easy but inefficient for us to do this after running gdal dem for our > polar grids at latitude -90, and a more general solution would require a > general approach to "where north is" for any location in a projection. > > I'll be able to modify GDAL to do this as an option to gdaldem for a > simple polar grid (e.g. EPSG:3031), and that will make our use of it much > more efficient. Is there any interest in a more general approach? > > Best, Mike > > > > -- > Michael Sumner > Software and Database Engineer > Australian Antarctic Division > Hobart, Australia > e-mail: mdsum...@gmail.com > > _______________________________________________ > gdal-dev mailing > listgdal-dev@lists.osgeo.orghttps://lists.osgeo.org/mailman/listinfo/gdal-dev > > -- http://www.spatialys.com > My software is free, but my time generally not. > > _______________________________________________ > gdal-dev mailing list > gdal-dev@lists.osgeo.org > https://lists.osgeo.org/mailman/listinfo/gdal-dev >
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