[GRASS-user] flowdirection

Maciej Sieczka tutey at o2.pl
Wed Dec 6 16:17:56 EST 2006


Hamish wrote:
> Manuel Seeger wrote:
>> another thing. when I use Terraflow with MFD, how are the
>> flowdirections expressed in the flowdirection grid? I get values
>> between -1 and 255, but I'm  not really shure how to treat them/ what
>> they express.
> 
> M.D.F.= multi-dimensional flow
> 
> MDF directions:
>  (based upon the rules in r.terraflow's findDominant() funtion in
> direction.cc)
> 
>    32 64 128
>    16 *   1
>    8  4   2
> 
> so a value of 255 is flow in all directions, a value of 3 is E and SE, a
> value of 65 is E and N, etc. I'm not sure exactly what 0 and -1
> represent, hopefully that becomes obvious.
> 
> The r.terraflow help page talks about MDF a bit, it should really have
> this info too.

Working on it. There was quite a bit to cleanup in the r.terraflow's
description.html anyway.

Could someone please say what 0 and -1 represent, which Hamish asks, so
I include this in the manual? Is null possible?

And how is the flow direction coded in case of SFD? Same as MFD, only
no multiple directions, thus only 1,2,4,8,16,32,64,128 direction is
possible? (that's what I assume...).

Please find the attached description.html + pngs and comment them.

Maciek
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