Re: [GRASS-user] Extraction 3D vectors ridges/Thalweg from raster DEM ?

[Markus Neteler]

On Fri, Dec 13, 2013 at 4:47 PM, Micha Silver  wrote:
> As far as I know, the shapefile format does not really support 3D vectors.

To my knowledge you can write out the 3D SHAPE file right away:

http://grass.osgeo.org/grass64/manuals/v.out.ogr.html
-z Create 3D output if input is 3D (applies to Shapefile output only)

EXAMPLES
-> Export to Shapefile
--> Export 3D faces from GRASS vector map to Shapefile format,
automatic 3D setting:

   v.out.ogr input=objects_3d type=face dsn=faces_3d.shp -z

hope this helps,
Markus
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Re: [GRASS-user] Extraction 3D vectors ridges/Thalweg from raster DEM ?

[image]

Hello,

Ok sorry i checked again the settings and this time i can read into my new
vector indeed 3 new colums. But unfortunatly, the values are NULL...;-(

 



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Re: [GRASS-user] Extraction 3D vectors ridges/Thalweg from raster DEM ?

[image]

Hello,

Sorry to disturb you again. But when i type the command, i have an error
message saying : The file is not found. 

Please see below the SS. It's strange beacause settings seems ok (location,
mpaset,db). 

 



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Re: [GRASS-user] Extraction 3D vectors ridges/Thalweg from raster DEM ?

[Micha Silver]

  
  
On 12/13/2013 06:33 PM, image wrote:


  Ok thanks. 

And acording to you, is it possible to add the field HeightZ to my vector3D
Grass generated? 



Yes, you do this as follows:
v.db.addcol map= columns="x_coord double
precision, y_coord double precision, z_coord double precision"
v.to.db map= option=coor columns="x_coord,
y_coord, z_coord"


  
Thanks? 



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Re: [GRASS-user] Extraction 3D vectors ridges/Thalweg from raster DEM ?

[image]

Ok thanks. 

And acording to you, is it possible to add the field HeightZ to my vector3D
Grass generated? 

Thanks? 



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Re: [GRASS-user] Extraction 3D vectors ridges/Thalweg from raster DEM ?

[Micha Silver]

  
  
As far as I know, the shapefile format
  does not really support 3D vectors.
  
  On 12/13/2013 05:41 PM, image wrote:


  Hello,

And thank you again for your help. I have a last little question. I succeed
in generating with grass vector 3D. I would like now export it to
shapefile3D. Do you know how to do that? 

Thanks. 





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Re: [GRASS-user] Extraction 3D vectors ridges/Thalweg from raster DEM ?

[image]

Hello,

And thank you again for your help. I have a last little question. I succeed
in generating with grass vector 3D. I would like now export it to
shapefile3D. Do you know how to do that? 

Thanks. 





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Re: [GRASS-user] Extraction 3D vectors ridges/Thalweg from raster DEM ?

[Micha Silver]

  
  
Hi
  
  On 12/13/2013 01:14 PM, image wrote:


  Hello,

Thank you very much for your reply. I made some tests following your
recommandations. For information, the surface of my raw raster DEM is 15.000
km². Resolution : 1 pixel X & pixel Y = 30 meters. (SRID 2154 UTM).

1/"r.watershed": the main input parameter seems to be the minimum size for
each basin. I typed 10 (unit pixels i think). I think it's a low value. I
would like know how enter a coherent value. How to ensure that our input
value is coherent?



You choose the threshold value as the minimum size of drainage area
that is of interest. In your case, with resolution 30m, then 1 pixel
= 900 sq.m. So a threshold of 11000, for example, would give a
minimum drainage area of 10 sq km.
(A threshold of 10 is way too small!)

  

  
2/"r.watershed" process generates several new raster layers. Could you
confirm to me that for *streams* r.thin & r.to.vect process i have to select
the third layer generated called "water_segments". And for the basins i have
to select the 4th layer called "Basin label"? 

The names of the basin and stream rasters are whatever you entered
as the "basin=..." and "stream=..." parameters

I suggest that you have a look at the manual page:
http://grass.osgeo.org/grass65/manuals/r.watershed.html
 

  

3/For basins and the v.extract process. I made a test with v.extractwhere.
But i don't find how to enter the value type=boundary. For information i'm
working with easy GUI interface via Qgis., no with command lines interface.

Perhaps for this job you could try the actual GRASS interface. It's
a bit harder to learn, but well worth the effort...

  

4/ The final vector output data for streams seems to be rather coherent.
However, my basins vector segmentation seems to be really too detailed and
inexploitable.


Change the threshold value... If you need a very detailed stream
layer, you can run the module once with a small thresh for streams,
then a second time with a large thresh to delineate the basins.

And one more thought: If you can manipulate the original DEM, so
that areas with zero value or no values (all the lower left corner,
etc), are actually set to NULL, then you will avoid those funny
straight stream segments.


  
Please find below usefull SS showing : A: My raster raw data /
B:Streams_vect_3D / C: Basins_labels_raster D: Basins_area_vector

A
 

B
 

C
 

D
 



If you can throw light for me. Thanks.

With kind regards. 




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Re: [GRASS-user] Extraction 3D vectors ridges/Thalweg from raster DEM ?

[image]

Hello,

Thank you very much for your reply. I made some tests following your
recommandations. For information, the surface of my raw raster DEM is 15.000
km². Resolution : 1 pixel X & pixel Y = 30 meters. (SRID 2154 UTM).

1/"r.watershed": the main input parameter seems to be the minimum size for
each basin. I typed 10 (unit pixels i think). I think it's a low value. I
would like know how enter a coherent value. How to ensure that our input
value is coherent?

2/"r.watershed" process generates several new raster layers. Could you
confirm to me that for *streams* r.thin & r.to.vect process i have to select
the third layer generated called "water_segments". And for the basins i have
to select the 4th layer called "Basin label"? 

3/For basins and the v.extract process. I made a test with v.extractwhere.
But i don't find how to enter the value type=boundary. For information i'm
working with easy GUI interface via Qgis., no with command lines interface.

4/ The final vector output data for streams seems to be rather coherent.
However, my basins vector segmentation seems to be really too detailed and
inexploitable.

Please find below usefull SS showing : A: My raster raw data /
B:Streams_vect_3D / C: Basins_labels_raster D: Basins_area_vector

A
 

B
 

C
 

D
 



If you can throw light for me. Thanks.

With kind regards. 




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Re: [GRASS-user] Extraction 3D vectors ridges/Thalweg from raster DEM ?

[Micha Silver]

On 12/12/2013 15:47, image wrote:

Dear all,

 From my Raster DEM, i would like extract Thalweg and Drainage divide
(ridges) 's 3D vectors.

According to you, is it possible to do that with grass?

Certainly

First use the r.watershed module to create streams and basins (rasters) 
from your DEM. Now do r.thin and r.to.vect on the streams raster to get 
a vector layer. Finally v.drape on that vector layer using the DEM to 
get a 3D vector result.


For the drainage divides, use r.to.vect on the basins raster to get an 
area vector of the basins. Then you can use v.extract type=boundary to 
get just the boundary lines from the basins. And then, as above, v.drape 
to create the 3D vector of watershed boundaries.

In advance, Thank you.

Regards.



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[GRASS-user] Extraction 3D vectors ridges/Thalweg from raster DEM ?

[image]

Dear all,

>From my Raster DEM, i would like extract Thalweg and Drainage divide
(ridges) 's 3D vectors. 

According to you, is it possible to do that with grass? 

In advance, Thank you. 

Regards. 



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