[GRASS-user] Re: r.water.outlet and longitude / window issue
Daniel Lee
lee at isi-solutions.org
Sat Jul 2 14:12:48 EDT 2011
Hi Andy,
I think it's great that you've fixed the bug. I read your emails with
interest but, as it's not my area of expertise, I didn't write back. As far
as changes to the GRASS source goes, I do think that the grass-dev list
would be the right place to take up such issues. You'd have my blessing at
least ;)
Best,
Daniel
On Sat, Jul 2, 2011 at 8:10 PM, Andy Wickert <wickert at colorado.edu> wrote:
> SOLVED:
>
> Built and installed GRASS 6.4.2 from svn, and added a line as noted below;
> inserted at line 101 in 6.4.2 (see surrounding lines for context).
> Recompiled r.water.outlet and it works like a charm.
>
> It is totally obvious that this is not an issue that anyone on this list
> knows/cares about, so could someone at least let me know where to take it
> such that can get incorporated into the GRASS source and no one else has the
> same problem? I'm thinking the grass-dev list, but I'd rather not use a
> loudspeaker to have another conversation with myself if I can avoid it :)
>
> G_usage();
> exit(EXIT_FAILURE);
> }
>
> E = G_adjust_east_longitude(E,window.west); // <-- NEW LINE; for using
> lat/lon data that straddle the 180 meridian
>
> if (E < window.west || E > window.east || N < window.south ||
> N > window.north) {
>
>
> Andy Wickert
> PhD Candidate
> University of Colorado
> Geological Sciences & Institute of Arctic and Alpine Research
> 1560 30th St.
> Boulder, CO 80303
> Office: RL3-275
>
>
>
> On Sat, Jul 2, 2011 at 3:01 AM, Andy Wickert <wickert at colorado.edu> wrote:
>
>> So, in short, I think that we could add the following at line 106 in
>> main.c for r.water.outlet (see
>> http://trac.osgeo.org/grass/browser/grass/trunk/raster/r.water.outlet/main.c
>> ):
>>
>> if (window.east > 180 && G_projection()==3){
>> E = E+360;
>> }
>>
>> Or, if I understand G_adjust_easting(), then we might be able to skip all
>> of that and simply type:
>>
>> E = G_adjust_east_longitude(E,window.west);
>>
>> Sound like a good improvement?
>>
>> Andy
>>
>>
>> On Sat, Jul 2, 2011 at 2:16 AM, Andy Wickert <wickert at colorado.edu>wrote:
>>
>>> Made some progress on this myself; think that a solution will require
>>> some minor source code modifications.
>>>
>>> The main idea and my question to GRASS users/developers:
>>>
>>> I think that I better understand the r.water.outlet problem now. Briefly,
>>> I think a proper solution would require changing the r.water.outlet source
>>> code to deal with wraparound at the 180 meridian; as it stands, the code
>>> seems to be designed for northing/easting in projected coordinate systems.
>>> I'd be happy to change / recompile / test the source code; in that case,
>>> should I take this thread to the GRASS-dev list? I have found the
>>> programmer's manual, but if anyone has advice on how to start in on
>>> development in GRASS, I would greatly appreciate it.
>>>
>>> Slightly more info:
>>>
>>> I was able to make all the points work by specifying the window as
>>> W:-180, E:180. However, the drainage basins refused to cross the 180
>>> meridian. I am fairly sure that these are because (1) I need increasing
>>> Easting values to make r.water.outlet work, but (2) in order to provide
>>> continously increasing Easting values, I must make a discontinuity at the
>>> 180 meridian in the middle of my data set. This makes me think that if I
>>> changed main.c inside r.water.outlet to include G_adjust_easting() within
>>> some if statments (is lat/long projection & West value is greater than
>>> East), that this would solve the problem.
>>>
>>> The workaround, of course, is to shift all location references by 180
>>> degrees, perform calculations, and move everything back, but I'd like to try
>>> to make a more elegant/permanent solution.
>>>
>>> Andy
>>>
>>>
>>> On Tue, Jun 28, 2011 at 11:43 AM, Andy Wickert <wickert at colorado.edu>wrote:
>>>
>>>> OK - I think I figured out some of it. On my computer where
>>>> r.water.outlet DOES work, the west-longitudes are expressed as negative
>>>> 0-180, while on the computer where it doesn't work, they are expressed as
>>>> positive east-longitude 180-360.
>>>>
>>>> So: the question becomes, how do I choose how west-longitudes are
>>>> interpreted by GRASS?
>>>>
>>>> Thanks!
>>>>
>>>> Andy
>>>>
>>>>
>>>> On Mon, Jun 27, 2011 at 11:00 PM, Andy Wickert <wickert at colorado.edu>wrote:
>>>>
>>>>> Hi GRASS user-list,
>>>>>
>>>>> I think that I have run into a bug in either the computational window
>>>>> definition or the r.water.outlet program (or maybe something else) that has
>>>>> to do with defining degrees West as either positive (East-longitude >180) or
>>>>> negative.
>>>>>
>>>>> What happens is that, for example, I type:
>>>>> r.water.outlet drainage=$watershed_direction basin=temp_basin
>>>>> easting=196 northing=60 --verbose --overwrite
>>>>>
>>>>> And GRASS returns:
>>>>> WARNING: Warning, ignoring point outside window:
>>>>> -164.0000,60.0000
>>>>>
>>>>> This occurs no matter whether I specify the longitude as a positive
>>>>> East-longitude (as above), as a negative value (e.g.,-164), or as, e.g.,
>>>>> 164W. (196E is not allowed).
>>>>>
>>>>> The problem is not my window definition, which includes the point in
>>>>> question:
>>>>> proj: 3
>>>>> zone: 0
>>>>> north: 73:00:30N
>>>>> south: 49:59:30N
>>>>> east: 144:59:30W
>>>>> west: 162:59:30E
>>>>> cols: 3121
>>>>> rows: 1381
>>>>> e-w resol: 0:01
>>>>> n-s resol: 0:01
>>>>> top: 1
>>>>> bottom: 0
>>>>> cols3: 3121
>>>>> rows3: 1381
>>>>> depths: 1
>>>>> e-w resol3: 0:01
>>>>> n-s resol3: 0:01
>>>>> t-b resol: 1
>>>>>
>>>>> When I use r.what, it gives me East-longitudes (values >180) for
>>>>> regions to the East of the 180 meridian. But r.water.outlet insists on
>>>>> switching everything to negatives no matter what input I give it, which I
>>>>> think is a source of the problem.
>>>>>
>>>>> The strangest thing about this is that I ran into this problem while
>>>>> following a routine that I had written several months ago in Bash; last
>>>>> time, I ran r.water.outlet on North America (all in degrees-west land) with
>>>>> no problems at all. I just checked the computational region (window) files
>>>>> for that run, and they look very similar to the ones I am using now. I have
>>>>> no clue why I didn't run into this problem back then / why it is cropping up
>>>>> now; both computers are running GRASS 6.4.1 on Ubuntu Linux.
>>>>>
>>>>> Anyway, if anyone has any suggestions, I'm all ears. Many thanks in
>>>>> advance,
>>>>>
>>>>> Andy Wickert
>>>>>
>>>>
>>>>
>>>
>>
>
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--
B.Sc. Daniel Lee
Geschäftsführung für Forschung und Entwicklung
ISIS - International Solar Information Solutions
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E-Mail: Lee at isi-solutions.org
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