[GRASS-user] river profile, how to

[ambijat]

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.:-)

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... ;-)
>
> Moritz
>
>
>> Hope it helps
>>
>> On Sun, Apr 17, 2011 at 8:18 AM, ambijat <ambijat at hotmail.com
>> <mailto:ambijat at 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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>
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