[GRASS-dev] how to reproject a raster map with absolute numbers without losing data

[Moritz Lennert]

Le 8 décembre 2016 07:25:46 GMT+01:00, Glynn Clements <glynn at gclements.plus.com> a écrit :
>
>Moritz Lennert wrote:
>
>> Yes. Do we have any existing module to calculate area by pixel ? An
>> area() function in r.mapcalc would be nice...
>
>I notice that this has been added, but I'm not sure that it's adequate
>for this task.
>
>For anything other than lat-lon locations, G_area_of_cell_at_row()
>assumes that the area of a cell is constant over the region. That's
>true for equal-area projections, and not far off for small scales
>(where projection would be almost an affine transformation), but it
>could be quite far off at larger scales.


Do I understand correctly that you would like the function to return geodesic area in projected locations? That would be a nice feature, but I wouldn't make it the default.  I think most people would expect constant pixel area in such location, knowing (at least some) that there is inherent error in the projection.

Moritz