[GRASS-user] How to create polygon from two selected contour line

[Markus Metz]

On Sat, Feb 25, 2012 at 7:52 PM, Michael Barton <michael.barton at asu.edu> wrote:
> The trick for many things in GRASS is to "think raster" instead of thinking vector.
>
> Make a raster DEM from your map (if you don't already have one).
>
> Query the raster (e.g., with r.mapcalc or r.reclass) to create a raster of elevations between your contour lines (e.g., in r.reclass the specification 1000 thru 1500 = 1).

Nice solution! To do that for the full map with r.mapcalc and steps of
500 m, try

r.mapcalc "elevation.reclass = if(elevation < 0, (int(elevation / 500)
- 1) * 500, int(elevation / 500) * 500)"

followed by:
>
> Run r.to.vect on the queried map to turn it into an area.
>
> Michael

Markus M

>
>
>
> On Feb 25, 2012, at 10:00 AM, <grass-user-request at lists.osgeo.org> <grass-user-request at lists.osgeo.org> wrote:
>
>> Date: Sat, 25 Feb 2012 10:42:20 +0200
>> From: Maris Nartiss <maris.gis at gmail.com>
>> Subject: Re: [GRASS-user] How to create polygon from two selected
>>       contour line
>> To: Paolo Cavallini <cavallini at faunalia.it>
>> Cc: grass-user at lists.osgeo.org
>> Message-ID:
>>       <CAK8GbeCR-5p7QnTp6cQDLT16pZ=yMbrdsqPaT73d+cZbVWQTKQ at mail.gmail.com>
>> Content-Type: text/plain; charset=UTF-8
>>
>> Convert line type from line to boundary (v.type)
>> Digitize a pair of new boundaries between both contour lines to form a
>> enclosed area or use v.hull to get an outline for merging in (v.patch)
>> Add a centroid (digitize or v.centroids) to enclosed area.
>> Profit!
>>
>> Not the mos easy way, still possible.
>>
>> Maris.
>>
>> 2012/2/25 Paolo Cavallini <cavallini at faunalia.it>:
>>> Il 25/02/2012 08:45, SWAPAN GHOSH ha scritto:
>>>
>>>> Hello Grassuser,
>>>> Anybody can please help me " To create polygon from two selected contour
>>>> line " using grass comand..........
>>>
>>> I'm afraid I can't - I tried recently, no joy.
>>> Good luck, if you succeed please let us know.
>>> All the best.
>>>
>>> --
>>> Paolo Cavallini
>>> See: http://www.faunalia.it/pc
>>>
>>> _______________________________________________
>>> grass-user mailing list
>>> grass-user at lists.osgeo.org
>>> http://lists.osgeo.org/mailman/listinfo/grass-user
>>
>
> _____________________
> C. Michael Barton
> Visiting Scientist, Integrated Science Program
> National Center for Atmospheric Research &
> University Consortium for Atmospheric Research
> 303-497-2889 (voice)
>
> Director, Center for Social Dynamics & Complexity
> Professor of Anthropology, School of Human Evolution & Social Change
> Arizona State University
> www: http://www.public.asu.edu/~cmbarton, http://csdc.asu.edu
>
>
>
>
>
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