[GRASS-dev] latlon support

[Glynn Clements]

Markus Metz wrote:

> > Requiring code to explicitly use specialised (spherical-aware)
> > functions in place of +,-,<,>,== etc is not a realistic strategy.
> 
> It seems the display does so when zooming out or panning. The Chukchi 
> Peninsula and other features are copied around and displayed on both 
> sides,

This is currently done in the display library (lib/display/draw2.c).

> I haven't done that in the vector, there all features are present 
> only on one side. This is not a complaint about the display, I like it 
> that way.
> 
> I think my questioning started because the region settings including map 
> extends are restricted to the 180 degree lon and 90 degree lat limits 
> whereas vector operations can exceed these limits causing problems later 
> on. To make grass handling of latlon coordinates consistent all around, 
> either the limits on region settings must be relaxed (taking care of all 
> the associated risks) or latlon vector coords must be forced into the 
> latlon limits by some lower-level handling.

Alas, it isn't just the coordinates, but the topology. E.g. for
Antartica, you have to add south, east and west edges to get a closed
region in Euclidean space.

> The currently allowed mix is confusing.

Indeed.

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