[GRASS-user] the area of a polygon?

GRASS GRASS user
1

Dear friends,

how do you measure the area of a polygon in grass?

Best Regards
--
Corrado Topi

Global Climate Change and Biodiversity
Area 18,Department of Biology
University of York, York, YO10 5YW, UK
Phone: + 44 (0) 1904 328645, E-mail: ct529@york.ac.uk

2

On Tue, 2008-03-11 at 15:07 +0000, Corrado wrote:

Dear friends,

how do you measure the area of a polygon in grass?

Hi!

An example for hectares (read the manual of v.report for more)

v.report map=YourPolygonVector option=area units=h

Or use the "Query" button on the Map Display of your GIS manager if it
is about only one polygon.

Cheers

Nikos

3

You can use v.to.db with the -option=area, eventually with the -p flag
to print them only:
http://grass.osgeo.org/grass63/manuals/html63_user/v.to.db.html

2008/3/11, Corrado <ct529@york.ac.uk>:

Dear friends,

how do you measure the area of a polygon in grass?

Best Regards
--
Corrado Topi

Global Climate Change and Biodiversity
Area 18,Department of Biology
University of York, York, YO10 5YW, UK
Phone: + 44 (0) 1904 328645, E-mail: ct529@york.ac.uk
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4

Dear friends,

1) v.report does not allow for selecting only one polygon in a map with many
polygons.

2) the query button returns the length of the boundary, but not the area.

3) v.to.db does not allow for selecting only one polygon.

Am I doing something wrong?

On Tuesday 11 March 2008 15:07:30 Corrado wrote:

Dear friends,

how do you measure the area of a polygon in grass?

Best Regards

Best Regards
--
Corrado Topi

Global Climate Change and Biodiversity
Area 18,Department of Biology
University of York, York, YO10 5YW, UK
Phone: + 44 (0) 1904 328645, E-mail: ct529@york.ac.uk

5

On Dienstag, 11. März 2008 16:35:36 Corrado wrote:

Dear friends,

1) v.report does not allow for selecting only one polygon in a map with
many polygons.

2) the query button returns the length of the boundary, but not the area.

3) v.to.db does not allow for selecting only one polygon.

Am I doing something wrong?

perhaps this helps:

r.to.vect input= output=out feature=area
v.db.addcol map=out layer=1 'columns=area double'
v.to.db map=out type=point,line,boundary,centroid layer=1 qlayer=1 option=area
units=meters column=area
v.to.rast out output=out_area use=attr col=area --o

On Tuesday 11 March 2008 15:07:30 Corrado wrote:
> Dear friends,
>
> how do you measure the area of a polygon in grass?
>
> Best Regards

Best Regards

--
**********************************************************************

University of Wuerzburg
Institute of Geography
Department of Remote Sensing
Am Hubland
97074 Wuerzburg, Germany
@
German Aerospace Center (DLR)
German Remote Sensing Data Center (DFD)
Environment and Security (US)

Phone: +49-(0)931-888-4797
Fax: +49-(0)931-888-4961
Email: martin.wegmann@uni-wuerzburg.de

**********************************************************************

6

If you want to avoid to extract your polygon and then run v.report or
v.to.db on it, I suggest you to use QGIS. When you use "identify", it
gives you the area value too.
Anyway, you can inspect v.report and v.to.db, and look for your polygon cat...

2008/3/11, Corrado <ct529@york.ac.uk>:

Dear friends,

1) v.report does not allow for selecting only one polygon in a map with many
polygons.

2) the query button returns the length of the boundary, but not the area.

3) v.to.db does not allow for selecting only one polygon.

Am I doing something wrong?

On Tuesday 11 March 2008 15:07:30 Corrado wrote:
> Dear friends,
>
> how do you measure the area of a polygon in grass?
>
> Best Regards

Best Regards
--
Corrado Topi

Global Climate Change and Biodiversity
Area 18,Department of Biology
University of York, York, YO10 5YW, UK
Phone: + 44 (0) 1904 328645, E-mail: ct529@york.ac.uk

7

On Tue, 2008-03-11 at 15:35 +0000, Corrado wrote:

2) the query button returns the length of the boundary, but not the area.

If you are a bit more careful (given that your vector data are closed
polygons -- check with v.clean) and click inside the polygon it will
report you the area as well. It happened to me as well... but I was not
exactly picking a point inside the polygon and therefore the report was
indicating a boundary and its length.

8

G. Allegri wrote:

If you want to avoid to extract your polygon and then run v.report or
v.to.db on it, I suggest you to use QGIS. When you use "identify", it
gives you the area value too.

same with

d.mon x0
d.vect yourmap type=area
d.what.vect

and click on some free space: if you get the boundary or the centroid,
try again.

area for that polygon is reported at the top of the form.

(I assume the same for the GUI query tool, but I'm not sure)

Anyway, you can inspect v.report and v.to.db, and look for your
polygon cat...

Hamish

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