[OSGeo-Discuss] geospatial algorithm to create area midway boundaries from lines ?

Micha Silver tsvibar at gmail.com
Sat Mar 7 03:11:00 PST 2020

You might want to consider a different idea: convert the line vector to 
a raster, then apply the r.grow.distance module to "fill" all null 
pixels in between the line pixels with the cat value of the closest line.

Here's how it would work in the nc_basic_spm mapset, using the 'streams' 

g.mapset -p
g.region -ap rast=elevation

g.copy vect=streams,mystreams

v.to.rast mystreams output=streams_rast use=cat

r.grow.distance input=streams_rast value=theissen_areas

r.to.vect -s theissen_areas output=theissen_polys type=area

Here is what the result looks like:


HTH, Micha

On 3/7/20 1:16 AM, karsten wrote:
> Hi Pierre,
> I mean line segments like e.g. in a road or water GIS layer and they could
> be smooth or rather less smooth.
> The output I desire should be polygons and not lines. Overall I am looking
> for nothing exact here - any approximate interpolation about midway
> plus/minus would be fine...
> Karsten
> -----Original Message-----
> From: Pierre Abbat [mailto:phma at bezitopo.org]
> Sent: Friday, March 06, 2020 14:59
> To: discuss at lists.osgeo.org
> Cc: karsten
> Subject: Re: [OSGeo-Discuss] geospatial algorithm to create area midway
> boundaries from lines ?
> On Friday, 6 March 2020 17:36:15 EST karsten wrote:
>> Hi All,
>> a general geospatial question to all:
>> I am trying to find out if there is any existing geospatial algorithm
>> (in any open Open Source Geospatial software) that would allow to use
>> a network of lines as a start point and expand those in such a way
>> that I can create new area boundaries for each of the lines "coverage
>> area". What I mean with that is if one could "buffer" the lines out in
>> such a way to create boundaries where any potential buffers would meet
>> at the middle way point between the lines so that in the end I could
>> have an area within that is the starting line. On example could look
>> like this (5 hand drawn lines in red and corresponding colored areas
>> that I would want to create). Note that is exact but to communicate
>> the idea) see
>> http://terra5.terragis.net/sites/html/aeras_for_lines%20copy.png
> When you say "lines", do you mean polylines made of line segments, polyarcs,
> or polyspirals? If polyarcs, will they generally be smooth? If polyspirals,
> will adjacent spiralarcs osculate, just be tangent, or neither?
> What sort of lines would the output be? If the input is polyarcs, the output
> could contain pieces of hyperbola. If the input is polyspirals, the output
> could contain strange indescribable curves. The only curves used as land
> boundaries are line segments and circular arcs, so they'd have to be
> approximated.
> Pierre
> --
> When a barnacle settles down, its brain disintegrates.
> Já não percebe nada, já não percebe nada.
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Micha Silver
Ben Gurion Univ.
Sde Boker, Remote Sensing Lab
cell: +972-523-665918

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