[GRASS-user] r.terraflow: several questions for understanding + info about TerraSTREAM

Moritz Lennert mlennert at club.worldonline.be
Wed Jun 25 08:34:24 EDT 2008


I have a few questions trying to understand r.terraflow details:

1) SFD

r.terraflow offers the possibility to work with single flow direction 
(SFD) instead of multiple flow direction (MFD). However, the drainage 
direction output map is strictly identical in both modes, indicating 
combinations of multiple directions. So, at which stage of r.terraflow 
does SFD come to play ? Only during accumulation calculation ? Would it 
be possible to output an SFD direction map from r.terraflow (I know of 
Hamish's Matlab script, but would be nice to have this directly in the 
module) ?

2) Terminology issue

The man page says this:

"Flow directions are computed using either the MFD (Multiple Flow 
Direction) model or the SFD (Single Flow Direction, or D8) model."

I'm no expert in flow routing, but it seems weird to equate D8 to SFD. I 
would have thought that D8 designates the number of possible directions 
(8 as opposed to 4 in D4 or ininite in D-Infinity) and that SFD/MFD 
designates the number of directions actually chosen for routing.

3) Weighting of directions

I can't find any information in the man page on whether flow in MFD is 
weighted by slope, i.e. whether the amount of water attributed to a 
particular direction depends on the slope, or whether the amount is just 
equally divided amongst all directions.

4) TerraSTREAM

Finally, are there any plans to integrate the GRASS implementation of 
TerraSTREAM (http://www.madalgo.au.dk/Trac-TerraSTREAM/wiki) into the 


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