[GRASS-user] How to list all unique pixel values (of a raster) covered by polygons (areas) for each polygon separately(?)

[G. Allegri]

About point 4), you can do it simply adding (v.db.addcol) at the
beginning of your job, then insert something like this into the loop:

echo "UPDATE (your_table) SET pixval=(what_you_want_to_upload) WHERE
FID=$i" | db.execute

Inside "what_you_want_to_upload" you can grab what you want from the
r.stats output (i.e. the values range).

The pixval column type depends on what kind of information you want to
insert. If a value range you set it as string type, or whatelse...

2008/1/18, Nikos Alexandris <nikos.alexandris at felis.uni-freiburg.de>:
> Giovanni,
>
> thank you for your proposal.
>
> The link to the FAQ (the one that Jose provided) looks like a solution.
>
> But your idea is clever as well and I had a similar way in my mind.
>
> If I got it correct you suggest:
>
> 1. VectorTargetAreas  ~~~v.to.rast (based on unique attribute like cat
> or FID~~~> RasterTargetAreas (all pixels of a "TargetArea" have now the
> same value
>
> 2.MASK out everything besides the "TargetAreas" ---looping to create as
> many MASKS as the the number of the "TargetAreas"
>
> 3.  For each MASK run r.stats
>
> 4 (I would also like to have) add the output list(s) as a new table
> (column pixval) into the initial VectorTargetAreas (with db.connect,
> db.addcol, etc). Let's say for a polygons which covers 20 pixels it
> would be like:
>
> FID - cat - pixval
> 1    -     1 -    200
> 2    -     1 -    198
> 3    -     1 -    234
> ..    -     .. -      .....
> 20 -      1 -    765
>
>
> Is it possible to put all this together?
>
>
> r.stats and output into a new column (pixval)
> On Thu, 2008-01-17 at 18:25 +0100, G. Allegri wrote:
> > Just a rapid idea.
> > You could make just one rasterized map of your polygons and then
> > insert in a loop this, giving each pixel a unique category value:
> >
> > r.mapcalc "MASK = if(raster=$i,1,null())"
> > with $1 the cat value (deriving from you original polygon)
> >
> > and then run r.stats, which will work only for the un-masked pixels.
> >
> > I don't have time to try this method, hope it helps.
> > GIovanni
> >
> > 2008/1/17, nikos.alexandris at felis.uni-freiburg.de
> > <nikos.alexandris at felis.uni-freiburg.de>:
> > > Salut Jose!
> > >
> > > This is what I am doing... and I only have 7 polygons - so
> > > it is ok.
> > >
> > > But if I have 50 polygons... I am not so sure how to script
> > > it to get (finally) a table with all pixels for each unique
> > > polygon for 2 different images of the same location (for
> > > raster MODIS year 2006 and then another of the same area
> > > MODIS 2007!).
> > >
> > > I want to run a regression with the pixel values... (pairs
> > > of 2006 and 2007 values).
> > >
> > > Thank you,
> > >
> > > Nikos.
> > >
> > >
> > >
> > > On Thu, 17 Jan 2008 16:42:31 +0000
> > >  "Jose Gomez-Dans" <jgomezdans at gmail.com> wrote:
> > > > On Jan 17, 2008 4:30 PM,
> > > > <nikos.alexandris at felis.uni-freiburg.de> wrote:
> > > >
> > > > > How can I get listed all unique pixel values enclosed
> > > > in
> > > > > each of the polygons I digitised (and for which the
> > > > univ.
> > > > > stats are calculated)?
> > > > >
> > > >
> > > > Can't you just rasterise your polygons, and use that as a
> > > > mask with
> > > > r.mapcalc? You can loop around in your shell. I tend to
> > > > do that with python,
> > > > but it's similar in GRASS. You can also try starspan.
> > > > Or.... <
> > > > http://grass.gdf-hannover.de/wiki/Aggregate_Values>
> > > >
> > > > Cheers,
> > > > Jose
> > > >
> > > >
> > > >
> > > > --
> > > > Centre for Terrestrial Carbon Dynamics
> > > > Department of Geography, University College London
> > > > Gower Street, London WC1E 6BT, UK
> > >
> > >
> > >                         .
> > >          Nikos Alexandris - Ph.D. Candidate
> > >                         .
> > >             Department of Remote Sensing
> > >                        and
> > >             Landscape Information Systems
> > >                      (FeLIS)
> > >                         .
> > >       Faculty of Forestry and Natural Environment
> > >           Albert-Ludwigs-University Freiburg
> > >                         .
> > >             Tel.  +49 (0) 761 203 3697
> > >             Fax.  +49 (0) 761 203 3701
> > >              Skype: Nikos.Alexandris
> > >                         .
> > >            Address: Tennenbacher str. 4
> > >               D-79106 Freiburg i. Br.
> > >                      Germany
> > >                         .
> > > _______________________________________________
> > > grass-user mailing list
> > > grass-user at lists.osgeo.org
> > > http://lists.osgeo.org/mailman/listinfo/grass-user
> > >
> --
> Nikos Alexandris
> .
> Department of Remote Sensing & Landscape Information Systems
> Faculty of Forestry & Environmental Sciences, Albert-Ludwigs-University Freiburg
> .
> Tel.  +49 (0) 761 203 3697 / Fax.  +49 (0) 761 203 3701 / Skype: Nikos.Alexandris
> .
> Address: Tennenbacher str. 4, D-79106 Freiburg i. Br., Germany
>
>