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

GRASS GRASS user
1

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).

Run r.to.vect on the queried map to turn it into an area.

Michael

On Feb 25, 2012, at 10:00 AM, <grass-user-request@lists.osgeo.org> <grass-user-request@lists.osgeo.org> wrote:

Date: Sat, 25 Feb 2012 10:42:20 +0200
From: Maris Nartiss <maris.gis@gmail.com>
Subject: Re: [GRASS-user] How to create polygon from two selected
  contour line
To: Paolo Cavallini <cavallini@faunalia.it>
Cc: grass-user@lists.osgeo.org
Message-ID:
  <CAK8GbeCR-5p7QnTp6cQDLT16pZ=yMbrdsqPaT73d+cZbVWQTKQ@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@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

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_____________________
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

2

On Sat, Feb 25, 2012 at 7:52 PM, Michael Barton <michael.barton@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@lists.osgeo.org> <grass-user-request@lists.osgeo.org> wrote:

Date: Sat, 25 Feb 2012 10:42:20 +0200
From: Maris Nartiss <maris.gis@gmail.com>
Subject: Re: [GRASS-user] How to create polygon from two selected
contour line
To: Paolo Cavallini <cavallini@faunalia.it>
Cc: grass-user@lists.osgeo.org
Message-ID:
<CAK8GbeCR-5p7QnTp6cQDLT16pZ=yMbrdsqPaT73d+cZbVWQTKQ@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@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@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

_______________________________________________
grass-user mailing list
grass-user@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-user