[GRASS-user] to separate a polygon

GRASS GRASS user
1

Hello,
I would like to separate a polygon that represents a road network into several polygons or polylines. I do not know what functions to use to display vertices and nodes.
Thank you in advance for answers that guide me.

Yvan

2

Yvan,
could you please state your intention ? and clarify how your network is
represented : are roads delimited by polygon boundaries and crossroads
by nodes ? or was the network digitized as a polygon (I mean giving
roads thickness) ?

First, about data type conversion, you can have a look at v.type.

Yours,
Vincent.

Le mardi 09 février 2010 à 15:14 +0100, Yvan Paillé a écrit :

Hello,
I would like to separate a polygon that represents a road network into
several polygons or polylines. I do not know what functions to use to
display vertices and nodes.
Thank you in advance for answers that guide me.

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

3

AFAIU :
* your network was digitized as a single polygon, contouring
streets/roads and crossroads in one go ;
* you would like to turn it into a linear reference network.
Am I right ?
If no special splitting was initially performed on boundaries to
distinguish between connected street sections I fear you'll have to do
things manually...

Vincent

Le mardi 09 février 2010 à 16:03 +0100, Yvan Paillé a écrit :

My road network was digitized into a polygon. Initially, I need to
separate into two distinct parts by half. In a second time, I need to
cut each polygon based on the streets and of belonging to adjacent
parcels. As if I would define a sidewalk.

Only the first step is already causing me problems.

Thank you

Yvan

Vincent Bain a écrit :
> Yvan,
> could you please state your intention ? and clarify how your network is
> represented : are roads delimited by polygon boundaries and crossroads
> by nodes ? or was the network digitized as a polygon (I mean giving
> roads thickness) ?
>
> First, about data type conversion, you can have a look at v.type.
>
> Yours,
> Vincent.
>
>
> Le mardi 09 février 2010 à 15:14 +0100, Yvan Paillé a écrit :
>> Hello,
>> I would like to separate a polygon that represents a road network into
>> several polygons or polylines. I do not know what functions to use to
>> display vertices and nodes.
>> Thank you in advance for answers that guide me.
>>
>> Yvan
>> _______________________________________________
>> grass-user mailing list
>> grass-user@lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/grass-user
>>

4

well,
depends on what accuracy you require, but an automated method could
however fit your needs :
v.to.rast -> r.thin -> r.to.vect -> v.clean

i.e :
turn your polygon into a raster map,
perform a thinning on the resulting map,
turn back this rasterized/thinned network into a vector map,
optionnally clean extra nodes with v.clean.

Hope this helps,
Good luck,

Vincent

Le mardi 09 février 2010 à 16:41 +0100, Yvan Paillé a écrit :

Yes, that's it!
Good well, I'll take my pain with patience and digitize point by point.

Thank you

yvan

Vincent Bain a écrit :
> AFAIU :
> * your network was digitized as a single polygon, contouring
> streets/roads and crossroads in one go ;
> * you would like to turn it into a linear reference network.
> Am I right ?
> If no special splitting was initially performed on boundaries to
> distinguish between connected street sections I fear you'll have to do
> things manually...
>
> Vincent
>
>
> Le mardi 09 février 2010 à 16:03 +0100, Yvan Paillé a écrit :
>> My road network was digitized into a polygon. Initially, I need to
>> separate into two distinct parts by half. In a second time, I need to
>> cut each polygon based on the streets and of belonging to adjacent
>> parcels. As if I would define a sidewalk.
>>
>> Only the first step is already causing me problems.
>>
>> Thank you
>>
>> Yvan
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> Vincent Bain a écrit :
>>> Yvan,
>>> could you please state your intention ? and clarify how your network is
>>> represented : are roads delimited by polygon boundaries and crossroads
>>> by nodes ? or was the network digitized as a polygon (I mean giving
>>> roads thickness) ?
>>>
>>> First, about data type conversion, you can have a look at v.type.
>>>
>>> Yours,
>>> Vincent.
>>>
>>>
>>> Le mardi 09 février 2010 à 15:14 +0100, Yvan Paillé a écrit :
>>>> Hello,
>>>> I would like to separate a polygon that represents a road network into
>>>> several polygons or polylines. I do not know what functions to use to
>>>> display vertices and nodes.
>>>> Thank you in advance for answers that guide me.
>>>>
>>>> Yvan
>>>> _______________________________________________
>>>> grass-user mailing list
>>>> grass-user@lists.osgeo.org
>>>> http://lists.osgeo.org/mailman/listinfo/grass-user
>>>>
>>