[GRASS-user] filling inter-contour area with constant value

Huidae Cho grass4u at gmail.com
Wed Apr 30 12:03:33 PDT 2014


Ah.. if you have two adjacent contour lines that are farther than the
contour interval from each other, my method doesn't work. For example, 100,
102, and 106 will become 101, 103, and 107, not 101, 104, and 107 (what
should the max value be?).

Huidae

On Wed, Apr 30, 2014 at 2:50 PM, Huidae Cho <grass4u at gmail.com> wrote:

> Venka,
>
> Let's say you have the elevation field in your shapefile and the contour
> interval is 2 meters.
>
> # Import your shapefile into GRASS
> v.in.ogr dsn=contours.shp output=contours type=boundary
>
> # Add centroids to the imported boundaries to make areas
> v.centroids input=contours output=contourareas
>
> # Convert the contour areas to raster filling inter-contour areas with
> contour elevations
> v.to.rast input=contourareas output=contourareas use=attr
> attrcolumn=elevation
>
> # Now you want to add a half of the contour interval to get what you want
> r.mapcalc expression="contoursteps=contourareas+1"
>
> contoursteps is what you need, I think.
>
> Regards,
> Huidae
>
>
>
> On Tue, Apr 29, 2014 at 4:19 AM, Moritz Lennert <
> mlennert at club.worldonline.be> wrote:
>
>> [Please keep threads on the list]
>>
>> On 29/04/14 00:33, John Ciolek wrote:
>>
>>> Hi Moritz.
>>>
>>> What do you mean by the following suggestion?
>>>
>>>
>>> On Apr 28, 2014, at 2:45 AM, Moritz Lennert wrote:
>>>
>>>  - if necessary, add a line at the edge of the region and patch that
>>>> with your contour lines to close polygons (v.in.region, v.patch)
>>>>
>>>
>>> Are you suggesting that you can close a contour (connect the beginning
>>> point to the ending point) using v.in.region or v.patch?
>>>
>>
>> No, not the beginning point to the end point. Either you have closed
>> contours or your contours go over the edge of your current region, meaning
>> that some contours are not closed. So, in order to close them, you can do
>> so arbitrarily at the edge of your region by patching in a line that
>> represents that edge. This line can be created with v.in.region.
>>
>>
>> Moritz
>> _______________________________________________
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>> grass-user at lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/grass-user
>>
>
>
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