[GRASS-user] to define a region which is not rectangular

[Hamish]

FAROUX STEPHANIE wrote:
> In my raster map sea pixels and missing data have the same
> null value. I'd like to separate the two but i don't
> have a sea/land mask. Missing data are concentrated in some areas.
> How can i do it?
> I thought to define regions in which missing data would be
> gathered but if i only use the zoom to do it, it will take a long time.
> Maybe using vectors?

depending on how fine a coastline you need, you might try importing the
GSHHS dataset with the v.in.gshhs module from the GRASS wiki addons page.

convert lines to areas with v.type + v.centroids, then vector areas to
raster MASK with v.to.rast. you can use r.mapcalc to invert the MASK
to create both land and sea MASKs.


good luck,
Hamish