[GRASS-dev] v.to.rast for polygons not overlapping center of raster cell

[Markus Metz]

On Mon, Feb 26, 2018 at 11:40 PM, Veronica Andreo <veroandreo at gmail.com>
wrote:
>
> Hi devs,
>
> I have hundreds of vector maps corresponding to a time series of burned
areas in the state of Victoria, Australia. To be able to extract the number
of classes (diversity) and the most common LC/slope burned (mode), I need
to transform each polygon vector map to raster, then use r.statistics, then
use r.mapcalc "LC_mode = @bushfire_20000103_LC_mode" and then v.rast.stats
(could use v.rast.stats directly if it had mode and diversity) to get the
values.
>
> In any case, my problem arises when polygons do not overlap the center of
the cell and therefore I get null rasters out of v.to.rast [1].
Consequently I cannot get info of LC and slope classes for those polygons.
>
> Is there a way to avoid this behavior in v.to.rast and be able to get
info for those polygons too? How can I get a list of all the polygons that
do not overlap the center of the grid cells to then use a different
approach for those ( if they are not too many :-/ )?

This can happen when the polygons are very small or very thin. You could
either discard these tiny polygons or increase the resolution of the
current region. With smaller raster cells, chances are higher that a cell
center will fall into these small polygons.

Markus M
>
> What would you recommend?
>
> Thanks a lot in advance!
> Vero
>
> [1] https://lists.osgeo.org/pipermail/grass-dev/2015-October/076676.html
>
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