[GRASS-user] Extract coordinates of vertices/nodes

GRASS GRASS user
1

Greetings,

Being quite in Grass, I am trying to find a way to extract geographic
coordinates of vertices and nodes (by the way I am struggling a little to
understand the differences between those two concepts) for polygons or
lines. Do you have any idea how to proceed?

Cheers

So.L.
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2

Hi Sophie,

v.out.ascii format=standard might help.

Here is the manual:
http://grass.itc.it/grass64/manuals/html64_user/v.out.ascii.html

Afterwards you can write a simple script to extract the coordinates from the
ascii-output.

schorschli
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3

On 04/28/2010 12:12 PM, Sophie Leguedois wrote:

Greetings,

Being quite in Grass, I am trying to find a way to extract geographic
coordinates of vertices and nodes (by the way I am struggling a little to
understand the differences between those two concepts) for polygons or
   

This might help:
http://grass.osgeo.org/wiki/Vectordata

lines. Do you have any idea how to proceed?
   

Probably with v.to.points -v

Cheers

So.L.
   
--
Micha Silver
http://www.surfaces.co.il/
Arava Development Co. +972-52-3665918

4

2010/4/28 Micha Silver <micha@arava.co.il>

On 04/28/2010 12:12 PM, Sophie Leguedois wrote:

Greetings,

Being quite in Grass, I am trying to find a way to extract geographic
coordinates of vertices and nodes (by the way I am struggling a little to
understand the differences between those two concepts) for polygons or

This might help:
http://grass.osgeo.org/wiki/Vectordata

In short, vertices are all the points that make up a line, a line may
consist of one or more vertices. In GRASS, nodes are the start and end
points of a line, so each line is linked to two nodes. These nodes are
used internally to maintain vector topology:
http://grass.osgeo.org/grass64/manuals/html64_user/vectorintro.html
Section: Vector model and topology

lines. Do you have any idea how to proceed?

Probably with v.to.points -v

There is some useful information in the v.to.points manual about how
to link the extracted points to the original lines.

Markus M

5

Thank you very much for your useful answers. The commands v.to.point and
v.out.ascii are doing the trick!

About vertices and nodes, I noticed that you can have several nodes for the
boundary limit of a polygon. Why so? Is it beacuse the nature of the
neighbour polygon is different?

Regards,

So.L.

-----
Sophie Leguédois
Researcher - Inra (French National Institute for Agricultural Research)
Laboratoire Sols et Environnement (UMR 1120 LSE)
Ensaia - 2 avenue de la Forêt de Haye
BP 172 - 54505 Vandoeuvre-lès-Nancy - France
Tel: +33 (0)3 83 59 57 62
http://www.lse.inpl-nancy.fr/
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6

If a polygon has no other touching it, it should have 2 nodes and at least 2 verticies.

When polygons touch other polygons, topology comes into play. So when polygon B is adjacent to, and touching polygon A, that makes a node because it is a shared line segment between polygon A and B. The lines break with nodes when other features connect, to create topologically correct, non-overlapping polygons.

Mark

On Apr 30, 2010, at 8:15 AM, Sophie Leguedois <sophie.leguedois@ensaia.inpl-nancy.fr > wrote:

Thank you very much for your useful answers. The commands v.to.point and
v.out.ascii are doing the trick!

About vertices and nodes, I noticed that you can have several nodes for the
boundary limit of a polygon. Why so? Is it beacuse the nature of the
neighbour polygon is different?

Regards,

So.L.

-----
Sophie Leguédois
Researcher - Inra (French National Institute for Agricultural Research)
Laboratoire Sols et Environnement (UMR 1120 LSE)
Ensaia - 2 avenue de la Forêt de Haye
BP 172 - 54505 Vandoeuvre-lès-Nancy - France
Tel: +33 (0)3 83 59 57 62
http://www.lse.inpl-nancy.fr/
--
View this message in context: http://osgeo-org.1803224.n2.nabble.com/Extract-coordinates-of-vertices-nodes-tp4973423p4985298.html
Sent from the Grass - Users mailing list archive at Nabble.com.
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