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

Nikos Alexandris nik at nikosalexandris.net
Mon Feb 26 15:48:13 PST 2018

* Veronica Andreo <veroandreo at gmail.com> [2018-02-26 23:40:59 +0100]:

>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

Burned areas are the base maps?
And "cover" maps are then LC/slope?

Did you consider to use

r.mask vector=BurnedAreas [where="SomeColumn='SomeValue'"]

and then `g.region zoom=MASK` and then, maybe, grow a bit the region with the
new(est) `g.region pixels=` option and, finally, redo the MASK,

so at least to get the computational region to include all of it?

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

Vero, I recall some similar situation years ago (described somewhere in
a messy script in https://trac.osgeo.org/grass/ticket/804) with a
specific problem that lead to `g.region pixels=`, see:
the step-by-step process https://trac.osgeo.org/grass/ticket/789.

I hope this is not confusing more.

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