[GRASS-stats] How to give projection to polygons and calculate area

[Nicolás Mari]

Dear Markus and Hamish,

Thanks a lot.

I am working with vectors.

How can i give the parameters of the new location via g.proj -c? for
example for a laea projection? (All inside R via execGRASS)

when i have the new location a use v,proj.

And then i use v.db.addcol to add a column called area.

then i use v.to.db to calculate it.

Do you think that is allright?

Thanks for your help.

Nicolas




2013/5/22 Markus Metz <markus.metz.giswork at gmail.com>

> On Tue, May 21, 2013 at 11:54 PM, Hamish <hamish_b at yahoo.com> wrote:
> > Nicolás wrote:
> >> I am working with GRASS functions in R batch job:
> >> I need to calculate areas from polygons which are in a
> >> geographical projection. To do so, i would like to define a new
> >> projection (Lamert Azimutal Equal Area) to my polygons, and the
> >> to calculate areas.
> >
> > raster areas or vector areas?
> >
> > (GRASS's r.* modules generally deal with that and give the
> > correct area in sq-meters automatically, so no need to reproject;
> > the v.* modules generally/often do not [yet])
>
> A simple query by clicking on the polygon will give square meters for
> latlon. v.to.db uploads values in meters or square meters for latlon,
> or miles, feet, acres, hectares when requested.
>
> Markus M
>
> >
> > if you'd like to make a new location in GRASS via a script,
> > you can use the g.proj module to do that (-c flag), then use
> > a GRASS_BATCH_JOB to automatically pull the vector map in with
> > v.proj and do the calculation.
> >
> >
> > Hamish
> > _______________________________________________
> > grass-stats mailing list
> > grass-stats at lists.osgeo.org
> > http://lists.osgeo.org/mailman/listinfo/grass-stats
>



-- 
Nicolás

*P** *Think before print
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