[GRASS-user] river profile, how to

GRASS GRASS user
1

Hi All,
I wish to develop a river profile from start point to its last. The GRASS 6.4.1 has a tool profile analysis, which is a bit crude. If I take two points, eg. river head and its last point then it gives a profile, but it is a direct and not along the course of the river. And, if I create a series of point all along the course, then certainly not the best values are there as selection process is very tedious. So, is there a method which would automatically take the raster values of the river course seen as a line and give a simple fine river profile.

Thanks

Ambrish Dhaka

2

If you have the shapefile for the river (or vector line in GRASS) you can convert it to points by using v.to.points and making the points really close to one another (make dmax small). then use v.what.rast to get the elevation at the points locations.
Hope it helps

On Sun, Apr 17, 2011 at 8:18 AM, ambijat <ambijat@hotmail.com> wrote:

Hi All,
I wish to develop a river profile from start point to its last. The GRASS 6.4.1 has a tool profile analysis, which is a bit crude. If I take two points, eg. river head and its last point then it gives a profile, but it is a direct and not along the course of the river. And, if I create a series of point all along the course, then certainly not the best values are there as selection process is very tedious. So, is there a method which would automatically take the raster values of the river course seen as a line and give a simple fine river profile.

Thanks

Ambrish Dhaka

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3

On 18/04/11 06:40, kapo coulibaly wrote:

If you have the shapefile for the river (or vector line in GRASS) you
can convert it to points by using v.to.points and making the points
really close to one another (make dmax small). then use /*v.what.rast*/
to get the elevation at the points locations.

Instead of v.what.rast, you can also use v.to.db+r.profile as follows (in GNU/Linux command line):

v.to.points myriver dmax=1 out=myriverpoints

v.to.db -p myriverpoints option=coor layer=2 | awk -F'|' '{print $2","$3}' | tail -n +2 | r.profile elevation out=myprofile.txt

adjust dmax to your needs.

Seems like a nice candidate for a simple Python AddOn script to me... :wink:

Moritz

Hope it helps

On Sun, Apr 17, 2011 at 8:18 AM, ambijat <ambijat@hotmail.com
<mailto:ambijat@hotmail.com>> wrote:

    Hi All,
    I wish to develop a river profile from start point to its last. The
    GRASS 6.4.1 has a tool profile analysis, which is a bit crude. If I
    take two points, eg. river head and its last point then it gives a
    profile, but it is a direct and not along the course of the river.
    And, if I create a series of point all along the course, then
    certainly not the best values are there as selection process is very
    tedious. So, is there a method which would automatically take the
    raster values of the river course seen as a line and give a simple
    fine river profile.

    Thanks

    Ambrish Dhaka
    _______________________________________________
    grass-user mailing list
    grass-user@lists.osgeo.org <mailto:grass-user@lists.osgeo.org>
    http://lists.osgeo.org/mailman/listinfo/grass-user

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

4

Thanks! All,
I developed a rather crude but a solid method. What I did was to actually convert the river raster into vector with r.to.vect.points. This automatically delivered me the altitude values for each point. Rest is then reverse engineering.:slight_smile:

Then I opened the dbf file in openoffice calc and added a distance column. I filled that column with the formula to add cumulative sum of resolution at each row (== to raster resolution). This gave me distance and altitude of each point.

Finally I plotted it nicely in chart of openoffice.
I think it was right approach. Any modifications?

regards,
Ambrish

On 4/18/2011 3:19 PM, Moritz Lennert wrote:

On 18/04/11 06:40, kapo coulibaly wrote:

If you have the shapefile for the river (or vector line in GRASS) you
can convert it to points by using v.to.points and making the points
really close to one another (make dmax small). then use /*v.what.rast*/
to get the elevation at the points locations.

Instead of v.what.rast, you can also use v.to.db+r.profile as follows (in GNU/Linux command line):

v.to.points myriver dmax=1 out=myriverpoints

v.to.db -p myriverpoints option=coor layer=2 | awk -F'|' '{print $2","$3}' | tail -n +2 | r.profile elevation out=myprofile.txt

adjust dmax to your needs.

Seems like a nice candidate for a simple Python AddOn script to me... :wink:

Moritz

Hope it helps

On Sun, Apr 17, 2011 at 8:18 AM, ambijat <ambijat@hotmail.com
<mailto:ambijat@hotmail.com>> wrote:

    Hi All,
    I wish to develop a river profile from start point to its last. The
    GRASS 6.4.1 has a tool profile analysis, which is a bit crude. If I
    take two points, eg. river head and its last point then it gives a
    profile, but it is a direct and not along the course of the river.
    And, if I create a series of point all along the course, then
    certainly not the best values are there as selection process is very
    tedious. So, is there a method which would automatically take the
    raster values of the river course seen as a line and give a simple
    fine river profile.

    Thanks

    Ambrish Dhaka
    _______________________________________________
    grass-user mailing list
    grass-user@lists.osgeo.org <mailto:grass-user@lists.osgeo.org>
    http://lists.osgeo.org/mailman/listinfo/grass-user

_______________________________________________
grass-user mailing list
grass-user@lists.osgeo.org
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