[GRASS-dev] latlon support

[Glynn Clements]

Markus Metz wrote:

> How about reversing the current policy? Restrict both raster and vector 
> maps to the 180 degree lon and 90 degree lat limit, that avoids 
> duplicate features within a map. Allow the region to be set anywhere 
> between -360 and 360 lon but restrict the width of the computational 
> region to 360 degrees lon to avoid duplicates.

That is problematic for computations which use a window (e.g. 
r.neighbors, r.proj, r.mfilter etc) on a whole-earth map. For that,
you need 360 degrees plus the width of the window.

[The same issue applies at the poles, but people don't normally care
about the poles if they're working in lat/lon.]

> Wrap map contents to the 
> current computational region if any map contents exist that fall into 
> the computational region. This would allow traversing the datum border 
> without gaps or breaks, e.g. for raster resampling. The display is not 
> affected, apart from "zoom to the current computational region".
> 
> I'm afraid you have thought of that possibility before and found flaws 
> in it. Apart from rewriting a lot of code...

AFAICT, the most important case to solve is when the region is set to
the Bering strait, and a vector map has Alaska at ~180W and Sibera at
~180E. Some of the data will need a 360-degree shift to obtain the
correct relative position.

-- 
Glynn Clements <glynn at gclements.plus.com>