[GRASS-user] How to get perimeter?

GRASS GRASS user
1

Hi List,

I'm searching for a way to delineate the perimeter of an area in a raster map. The area is like the result of r.clump, so it is caracterized by a integer number in the raster map. I have no problem in trasforming the raster map in vector with r.to.vect, but the vector is an area, not a line. I need to know the lenght of the contour of the areas. What is the best way to obtain that?

Thank you in advance

Margherita

--
Eng. Margherita Di Leo
Ph.D. Student Methods and Technologies for Environmental Monitoring
Department of Environmental Engineering and Physics (DIFA)

University of Basilicata Campus Macchia Romana
85100 - Potenza Italy

Office: +39-0971205363
Fax: +39-0971205160
E-mail: dileomargherita AT gmail DOT com
Skype: dileomargherita
URL: http://www.difa.unibas.it/A_Manager_PP.do?azione=visualizzaHomePage&id=106

2

v.report map=name option=length units=meters

On 9/17/09, Margherita Di Leo <diregola@gmail.com> wrote:

Hi List,

I'm searching for a way to delineate the perimeter of an area in a
raster map. The area is like the result of r.clump, so it is
caracterized by a integer number in the raster map. I have no problem in
trasforming the raster map in vector with r.to.vect, but the vector is
an area, not a line. I need to know the lenght of the contour of the
areas. What is the best way to obtain that?

Thank you in advance

Margherita

--
Eng. Margherita Di Leo
Ph.D. Student
Methods and Technologies for Environmental Monitoring
Department of Environmental Engineering and Physics (DIFA)

University of Basilicata
Campus Macchia Romana
85100 - Potenza
Italy

Office: +39-0971205363
Fax: +39-0971205160
E-mail: dileomargherita AT gmail DOT com
Skype: dileomargherita
URL:
http://www.difa.unibas.it/A_Manager_PP.do?azione=visualizzaHomePage&id=106

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--
cheers,
maning
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"Freedom is still the most radical idea of all" -N.Branden
wiki: http://esambale.wikispaces.com/
blog: http://epsg4253.wordpress.com/
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3

Margherita Di Leo wrote:

I'm searching for a way to delineate the perimeter of an
area in a raster map. The area is like the result of
r.clump, so it is caracterized by a integer number in the
raster map. I have no problem in trasforming the raster map
in vector with r.to.vect, but the vector is an area, not a
line. I need to know the lenght of the contour of the areas.
What is the best way to obtain that?

beware the dreaded fractal coastline problem.

especially if you are working with a raster map which is likely
to have saw-tooth edges.

it is better to compare areas. you might be able to compare perimeter
length as a ratio of other clumps on the same map, but that's about it.

http://en.wikipedia.org/wiki/How_Long_Is_the_Coast_of_Britain%3F_Statistical_Self-Similarity_and_Fractional_Dimension

Hamish