[GRASS-user] sample a strds at specific locations (areas)

Wed Feb 6 11:54:53 PST 2019

Ciao Madi, Vero,

Starting with GRASS 7.6, also centroids are used to get the raster representation of your area vector map. That increases the likelihood of smaller areas to be rasterized.
Increasing the resolution of the current region alone does not help, because v.rast.stats temporarily changes the computational region to align with the input raster map(s) (see also: https://trac.osgeo.org/grass/ticket/3523 and https://trac.osgeo.org/grass/ticket/3598 for discussion) Even if the first ticket is closed, comments are welcome.
It might make sense to add a flag to v.rast.stats like in r.slope.aspect to not align the computational region.

Furthermore, with regards to efficiency, v.strds.stats could gain some speed if multi-raster support in v.rast.stats - added in G 7.6 - would be handed down to the addon. Might almost double the speed for larger STRDS…

Cheers
Stefan

From: grass-user <grass-user-bounces at lists.osgeo.org> On Behalf Of Veronica Andreo
Sent: onsdag 6. februar 2019 17:20
To: Margherita Di Leo <diregola at gmail.com>
Cc: GRASS user list <grass-user at lists.osgeo.org>
Subject: Re: [GRASS-user] sample a strds at specific locations (areas)

Hi Madi

El mié., 6 feb. 2019 a las 16:31, Margherita Di Leo (<diregola at gmail.com<mailto:diregola at gmail.com>>) escribió:
I have a question regarding v.strds.stats. I get the following warning message:

WARNING: Not all vector categories converted to raster. Converted 120 of 265.

What could be the reason for that?

Some vector areas might not be converted because they are too small with respect to the pixel size that you try to query. Others will tell better but I think the polygon must overlap the center of the pixel in order to be converted into raster. One solution could be to resample your rasters to a higher resolution.
HTH,
Vero
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