[GRASS-user] how to calculate areas

GRASS GRASS user
1

hello
I have DEM of some part of mountains chain and i would like to calculate a real area of this (area in 3d not plane area).
I wonder if Grass can do it.
best
maciej

Maciej Tomaszczyk
Polish Geological Institute
Geological Mapping Department
http://www.pgi.gov.pl
http://www.opengeology.pl

2

Maciej Tomaszczyk wrote:

hello
I have DEM of some part of mountains chain and i would like to calculate a real area of this (area in 3d not plane area).
I wonder if Grass can do it.
best
maciej

Maciej Tomaszczyk
Polish Geological Institute
Geological Mapping Department
http://www.pgi.gov.pl
http://www.opengeology.pl

Just to clarify, you mean surface area as opposed to footprint of the
mountain range. So the sum of all the surfaces of the 3d model?

Alex

3

Alex Mandel wrote:

Maciej Tomaszczyk wrote:

hello
I have DEM of some part of mountains chain and i would like to calculate a real area of this (area in 3d not plane area).
I wonder if Grass can do it.
best
maciej

Maciej Tomaszczyk
Polish Geological Institute
Geological Mapping Department
http://www.pgi.gov.pl
http://www.opengeology.pl

Just to clarify, you mean surface area as opposed to footprint of the
mountain range. So the sum of all the surfaces of the 3d model?

Alex

The solution to that problem would be r.surf.area which should give you
both the 2D and 3D area.
You'll have to actually try this as I just read about it in Markus and
Helena's book.

Alex

4

to my mind, one has to be cautious with this module, and be aware of how
surfaces are estimated. It appears that results show a big variability
given the current region resolution.
(just try r.surf.area on a sloppy plane [generated with r.plane],
knowing its inclination and thus its actual surface in advance)

Bye,
Vincent

Le mardi 16 septembre 2008 à 02:28 -0700, Alex Mandel a écrit :

Alex Mandel wrote:
> Maciej Tomaszczyk wrote:
>> hello
>> I have DEM of some part of mountains chain and i would like to calculate a real area of this (area in 3d not plane area).
>> I wonder if Grass can do it.
>> best
>> maciej
>>
>> Maciej Tomaszczyk
>> Polish Geological Institute
>> Geological Mapping Department
>> http://www.pgi.gov.pl
>> http://www.opengeology.pl
>>
>>
>>
>
> Just to clarify, you mean surface area as opposed to footprint of the
> mountain range. So the sum of all the surfaces of the 3d model?
>
> Alex
>
>

The solution to that problem would be r.surf.area which should give you
both the 2D and 3D area.
You'll have to actually try this as I just read about it in Markus and
Helena's book.

Alex
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