[GRASS-user] Python-Loop over points

Wed Apr 6 09:58:01 EDT 2011

Hej again,

I've got a first basic idea but it isn't working yet completetly.
I wanted to loop over the pointfile to use the single points for other operations
like the r.stream.basins module. Most of these modules do also except coordinates.

So here is one solution but hopefully someone know a better one:

1) add two new columns to the pointsfile and populate it with the X and Y coordinate (v.db.addcol and v.to.db)

2) use v.db.select-command in a for loop and pipe the X.Y coordinate-pair to a variable, like (to loop over the first 5 points in a pointfile):

def main():
    for i in range(5):
        where ="rowid = "+str(i)
        p = grass.pipe_command("v.db.select", flags="c", map=options['input'], columns="X,Y", where=where, fs=",")
        print p

It isn't working at the moment (I get <grass.script.core.Popen object at 0x53f3f0>) but I don't think that is a problem of the for loop, it is more a problem of the pipe-command because it is working when i use run_command instead of pipe_command.

what is the problem with the pipe command? is there a simpler way to loop over points to use them in other modules?

Am 06.04.2011 um 12:48 schrieb Johannes Radinger:

> Hello,
> 
> I want to reactive this thread...
> and want just to put in some new ideas...and i still want to use a for-loop 
> or something similar on a point-vector-file in a Python-script
> 
> i want something like Daniel mentioned but want to loop over points within one single pointfile:
> 
>   for point in "points_file": 			--> that is the line I don't know, I want to get point per point and it's ID
> 	grass.run_command("r.streams.basins", dir = "flow_direction, points=point_ID, basins = out_map_ID)
> 
> @Stephen sefick: do you have solved that issue already?
> 
> I think that is a quite common problem, therefore I think there must be a quite simple solution....
> is a point-file a loopable element? how would an example look like?
> I am looking for a similar approach what ArcGIS is using now in their new modeller (Iterator).
> 
> 
> /johannes
> 
> 
> Am 22.02.2011 um 15:57 schrieb stephen sefick:
> 
>> Why not create a temporary vector map from the larger vector map in
>> the for loop;  do what needs to me done; clean up.
>> 
>> I would be interested in you solution, and could offer some help if
>> you would like.  I am going to have to process similar data.
>> HTH
>> 
>> Stephen
>> 
>> On Tue, Feb 22, 2011 at 1:35 AM, Johannes Radinger <JRadinger at gmx.at> wrote:
>>> 
>>> Am 22.02.2011 um 02:07 schrieb Daniel Victoria:
>>> 
>>>> I'm not sure but from what I read in the r.stream.basins description,
>>>> you can have more than one point in your vector file in roder to
>>>> delineate your basins. Now, in case you have one basin inside another,
>>>> what I did once was:
>>>> 1) get x,y coordinates of each point using v.out.ascii
>>>> 2) for each point run r.watershed...
>>> Yes, thats what I want as well, but I want to automatize it and not to run for each
>>> point manually. I also want to run
>>> for each point a grass-function (not necessarily r.stream etc.)
>>> I just want to know how it basically works to loop over points.
>>> 
>>> to things I thought:
>>> 1) loop over the ascii if that is possible
>>> 2) use the for loop in combination with v.db.select, but I don't know how that
>>> will work in python
>>> 
>>> /johannes
>>> 
>>> 
>>>> 
>>>> Cheers
>>>> daniel
>>>> 
>>>> On Fri, Feb 18, 2011 at 11:49 AM, Johannes Radinger <JRadinger at gmx.at> wrote:
>>>>> Hello,
>>>>> 
>>>>> 
>>>>> -------- Original-Nachricht --------
>>>>>> Datum: Mon, 7 Feb 2011 22:25:31 -0200
>>>>>> Von: Daniel Victoria <daniel.victoria at gmail.com>
>>>>>> An: Johannes Radinger <JRadinger at gmx.at>
>>>>>> CC: grass-user at lists.osgeo.org
>>>>>> Betreff: Re: [GRASS-user] Python-Loop over points
>>>>> 
>>>>>> Hi Johannes,
>>>>>> 
>>>>>> You will need to use for loop. Something like this (UNTESTED!)
>>>>>> 
>>>>>> for p in range(5):
>>>>>>    points_map = "point"+str(p)
>>>>>>    out_map = "output"+str(p)
>>>>>>    grass.run_command("r.streams.basins", dir = "flow_direction,
>>>>>> points=points_map, basins = out_map)
>>>>>> 
>>>>>> That should work, or at least something similar
>>>>>> 
>>>>>> Daniel
>>>>> 
>>>>> Thank you for your suggestions Daniel, I also thought about
>>>>> a for loop. But in your case the loop is using for each iteration
>>>>> a input-pointmap called "point"+str(p).
>>>>> 
>>>>> The difference in my
>>>>> case is that I've got only one vector map but with several points
>>>>> in it and I want to iterate over the single points.
>>>>> How is it possible to iterate over the single points? The points are
>>>>> stored in a kind of list format, so it should somehow be possible to
>>>>> loop over this file, but how?
>>>>> 
>>>>> any suggestions?
>>>>> 
>>>>> /johannes
>>>>> 
>>>>>> 
>>>>>> On Wed, Feb 2, 2011 at 9:39 AM, Johannes Radinger <JRadinger at gmx.at>
>>>>>> wrote:
>>>>>>> Hello,
>>>>>>> 
>>>>>>> I am performing e.g. the r.stream.basins calcutlation in python:
>>>>>>> 
>>>>>>>   grass.run_command("r.stream.basins",
>>>>>>>                     dir = "flow_direction",
>>>>>>>                     points = "point1",
>>>>>>>                     basins = "output")
>>>>>>> 
>>>>>>> that's working perfectly in the case of one single point in "point1".
>>>>>>> How can I do that multiple times when the point layer consist of e.g. 5
>>>>>>> points and I want to create an output for each point (create 5 output
>>>>>> rasters).
>>>>>>> 
>>>>>>> How can that be done in a python script?
>>>>>>> 
>>>>>>> 
>>>>>>> thank you
>>>>>>> 
>>>>>>> Johannes
>>>>>>> 
>>>>>>> --
>>>>>>> NEU: FreePhone - kostenlos mobil telefonieren und surfen!
>>>>>>> Jetzt informieren: http://www.gmx.net/de/go/freephone
>>>>>>> _______________________________________________
>>>>>>> grass-user mailing list
>>>>>>> grass-user at lists.osgeo.org
>>>>>>> http://lists.osgeo.org/mailman/listinfo/grass-user
>>>>>>> 
>>>>> 
>>>>> --
>>>>> NEU: FreePhone - kostenlos mobil telefonieren und surfen!
>>>>> Jetzt informieren: http://www.gmx.net/de/go/freephone
>>>>> 
>>> 
>>> _______________________________________________
>>> grass-user mailing list
>>> grass-user at lists.osgeo.org
>>> http://lists.osgeo.org/mailman/listinfo/grass-user
>>> 
>> 
>> 
>> 
>> -- 
>> Stephen Sefick
>> ____________________________________
>> | Auburn University                                         |
>> | Biological Sciences                                      |
>> | 331 Funchess Hall                                       |
>> | Auburn, Alabama                                         |
>> | 36849                                                           |
>> |___________________________________|
>> | sas0025 at auburn.edu                                  |
>> | http://www.auburn.edu/~sas0025                 |
>> |___________________________________|
>> 
>> Let's not spend our time and resources thinking about things that are
>> so little or so large that all they really do for us is puff us up and
>> make us feel like gods.  We are mammals, and have not exhausted the
>> annoying little problems of being mammals.
>> 
>>                                -K. Mullis
>> 
>> "A big computer, a complex algorithm and a long time does not equal science."
>> 
>>                              -Robert Gentleman
> 
> _______________________________________________
> grass-user mailing list
> grass-user at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/grass-user