[GRASS-user] Determine surface areas

[Nikolaus Arnold]

Hi!

I am new to using GIS and GRASS.
I am currently working on a task where I have to determine the type of 
surface around a specific coordinate. For example what is the total 
water surface area in a 100km radius around the Eiffeltower.
I have found a landcover map ( 
http://glcf.umiacs.umd.edu/data/landcover/ ) with a 1km raster that 
isn't perfect but should do the job. After some time I managed 
displaying the map and showing only specific values in GRASS. My next 
step would have been exporting the map to an image, draw the desired 
circles with a image editing tool and count the contained fields manually.
But taking a closer look at GRASS and the vectormap function, I wondered 
if it would be possible to create vector circles, merge them with the 
existing map and let GRASS do the work of counting the Areas.


Does this seem possible? If yes, what would be the first steps?

Any help would be very much appreciated
Kindest regards
Nikolaus
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Re: [GRASS-user] Determine surface areas

[Nikolaus Arnold]

Finally got it.

Import map:
v.in.dxf

created areas:
v.type input=map1 output=map2 type=line,boundary
v.clean input=map2 output=map3 tool=snap thresh=0.0001
v.centroids input=map3 output=map4 option=add

checked with v.digit (strangely v.centroids always categorized in the same
way, but in the outer ring it mixed up two areas, but that was easily
corrected by manually changing those two categories)

v.to.rast use=cat

masked with rastermap - watercellvalue

r.report


thanks a lot
Nikolaus


Am Freitag, 6. März 2009 09:25:45 schrieb Markus Metz:

Moritz Lennert wrote:
> On 05/03/09 23:15, i...@the-masterplan.net wrote:
>> Hi!
>>
>> I am still working on the extended problem and so far i have done the
>> following.
>> I created circles and sectors in autocad and imported the dxf file
>> (first
>> one sector at a time).
>> The import didn't seem to work that well, so i converted lines to
>> boundaries and used v.clean to get areas, and inserted a centroid with
>> v.digit and created a rastermap with v.to.rast (source: val, and
>> featuretype area).
>> using the rastermap as mask I can use r.report or r.stats to get the
>> waterarea/watercells.
>>
>> Because there are 160 of these areas i was wondering if there is a
>> possibility to use all of the areas at once (or at least more than
>> one at
>> a time) assign some kind of an ID to every area and get the results
>> separately for every area.
>> trying to use more than one area at a time always got me the total 

stats

>> for all areas.
>
> Just give each centroid a different category value (e.g. using
> v.category, or by hand using v.digit), then v.to.rast use=cat. Then
> r.stats/r.report should give you the result by category.

Or v.to.db option=area?

Markus M




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