[GRASS-user] Watershed delineation

[Daniel Victoria]

Hi Jaime and all grass users,

Well, I think that something has gone wrong then because the basin
numbering does not seam to be in a logical sequence. Or I have not
understood what is the logic in the numbering sequence.

The basin numbers starts from the top left and increase as it goes to
the bottom right. To aggregate the basins, the only thing that
occurred to me was slicing the data, say between 150000 and 160000. If
I do that in r.mapcalc I get a horizontal stripe...

I'm attaching 2 png files so you can understand what I mean. The first
is the output of the sink_basins with a rainbow color palette. The
second is a slice from basin 150000 to 160000

Just for the record, here is my g.region -p output:
projection: 99 (Polyconic (American))
zone:       0
datum:      wgs84
ellipsoid:  wgs84
north:      586373.26721103
south:      -3736322.77978473
west:       -2205571.78762371
east:       2448796.9570448
nsres:      899.99917697
ewres:      899.9166173
rows:       4803
cols:       5172
cells:      24841116

The resolution is strange because the DEM was projected from a 30
arcsec latlon map. I tried to set it to 900 meters but the output was
like this...

Cheers and thanks
Daniel

PS - This message has been re-sent because the first time it was too
big (attachments)


On Dec 26, 2007 11:13 PM, Jaime Carrera <jaicarrerahdez at yahoo.com> wrote:
> Hi Daniel,
>
> that's right; you end up with a lot of sub-basins, which you can aggregate
> according to your need. They are numbered on a logical sequence, so it's
> really easy to aggregate them with r.mapcalc; just check where a key outlet
> is and go upstream from there.
>
> Cheers,
> Jaime
>
> Daniel Victoria <daniel.victoria at gmail.com> escribió:
>
>  Hi all,
>
> I trying to delineate watersheds for several points in a very big DEM
>
>  | Data Type: CELL |
>  | Rows: 4803 |
>  | Columns: 5172 |
>  | Total Cells: 24841116
>
> I've successfully ran r.terraflow on the DEM but now I'm stuck. How do
> I get the watershed area for my points of interest? I've tried using
> the direction map produced with r.water.outlet but it did not work (I
> used MFD flow calculation).
>
> Also, from what I understood, the sink watershed map is suposed to be
> the watersheds delineated by the terraflow module, is that correct? It
> turns out that I have 191736 categories. Does that mean 191736 basins?
> Is there a way to aggregate them?
>
> Anyway, I think I'll let r.watershed run for the night
>
>
> Thanks and cheers
> Daniel
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