[GRASS-user] Centerlines of Polygons (skeletons)

GRASS GRASS user
1

Wondering if there is a simple way in GRASS to produce skeletons of Polygons (rivers/streams), to find the flow centerline.

thanks

Mars Sjoden
Aurora Geomatics
arorageo@telus.net
http://arorageo.blogspot.com/

2

Thank you to both Christian and Michael,

I suppose that is an avenue to go down, but then I suppose if I were to go the Raster route I may as well use the DEM file and do a quick hydro-analysis.

I wonder, is there a way to create a Voronoi diagram in GRASS?

hmmm,

Oh, is there a method to convert a polygon into a set of equidistant points? Either by distance or evenly spaced number of points?

I could then create thiessen polygons, clip to original polygon, convert thiessens to polylines, and select polylines that intersect polygon boundary... I suppose I would be left with somewhat of a centerline, although there would still be theissen polygon branches that extend towards the boundary and not run the centerline... Gosh I need to go back to Geometry class to figure this out...

Any geometry wizards out there?

Hi,

I only know the way for raster data using r.thin to get a center line
for e.g. wide raster streams.

Christian.

Am Mittwoch, den 18.06.2008, 10:24 -0700 schrieb Aurora Geomatics:

Wondering if there is a simple way in GRASS to produce skeletons of
Polygons (rivers/streams), to find the flow centerline.

thanks

Mars Sjoden
Aurora Geomatics
arorageo@telus.net
http://arorageo.blogspot.com/

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Mars Sjoden
Aurora Geomatics
aurorageo@telus.net
http://arorageo.blogspot.com/

3

On Wed, Jun 18, 2008 at 02:01:56PM -0700, we recorded a bogon-computron collision of the <aurorageomatics@telus.net> flavor, containing:

I wonder, is there a way to create a Voronoi diagram in GRASS?

Yes. With v.voronoi.

--
Tom Russo KM5VY SAR502 DM64ux http://www.swcp.com/~russo/
Tijeras, NM QRPL#1592 K2#398 SOC#236 AHTB#1 http://kevan.org/brain.cgi?DDTNM
"It's so simple to be wise: just think of something stupid to say and
  then don't say it." --- Sam Levinson

4

On 19.06.2008 00:01, Aurora Geomatics wrote:

I wonder, is there a way to create a Voronoi diagram in GRASS?

There is the v.voronoi module, which is also the subject of one of the Summer of Code projects this summer. I've been looking at an algorithm that creates Voronoi diagrams out of skeleton lines, but currently there is no direct support for skeleton lines in GRASS, as far as I can tell, perhaps if Martin P. gets interested he will develop this method and as a by-product a v.skeleton module, but that won't probably happen autumn if at all.

--Wolf

--

<:3 )---- Wolf Bergenheim ----( 8:>

5

This sounds very interesting, certainly I could see this really coming in handy when given a few thousand polygons of rivers and streams and asked to quickly output the centerlines… Finding centerlines of river/stream polygons may seem so simple for all this powerful computational equipment and software to clients, and perhaps it is to those who have higher math skills…

On 18-Jun-08, at 2:22 PM, Wolf Bergenheim wrote:

On 19.06.2008 00:01, Aurora Geomatics wrote:

I wonder, is there a way to create a Voronoi diagram in GRASS?

There is the v.voronoi module, which is also the subject of one of the Summer of Code projects this summer. I’ve been looking at an algorithm that creates Voronoi diagrams out of skeleton lines, but currently there is no direct support for skeleton lines in GRASS, as far as I can tell, perhaps if Martin P. gets interested he will develop this method and as a by-product a v.skeleton module, but that won’t probably happen autumn if at all.

–Wolf

Looks like some interesting material, I’ll have a read though this, see what I can use out of it for my situation. I noticed the issue of the “Branching” outside the Centerline/Skeleton came up, I’ll have to read deeper to see if or what the solution was for this issue.

Have a look at this old page

http://research.esd.ornl.gov/CRERP/DOCS/RIVERMI/P114.HTM

you could do the same thing in GRASS

Bill H.

Thanks Tom, I must have miss spelled when I searched it in the GRASS manual.

On Wed, Jun 18, 2008 at 02:01:56PM -0700, we recorded a bogon-computron collision of the <aurorageomatics@telus.net> flavor, containing:

I wonder, is there a way to create a Voronoi diagram in GRASS?

Yes. With v.voronoi.

–
Tom Russo

Mars Sjoden
Aurora Geomatics
aurorageo@telus.net
http://arorageo.blogspot.com/