[GRASS-user] Re: r.water.outlet and longitude / window issue

[Andy Wickert]

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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