[gdal-dev] gdaldem aspect is grid-oriented

[Thomas Knudsen]

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.rouault at 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: mdsumner at gmail.com
>
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> -- http://www.spatialys.com
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