[GRASS-dev] r.terraflow performance tweak

[roderikk]

Hi all,

I am trying to use r.terraflow now as well to analyse a very large dataset.
However, I run into the same issue as the OP. I get millions of warning
messages that are not really relevant, because a negative tci is in my eyes
just valid, however, adding an hour to my initial test run on a smaller
sample.

I think the check on line 143 of sweep.cc should see if the flow or the
slope are negative (giving rise to the log of a negative number resulting in
an error). I am not sure yet what a negative tci means, but a small flow
with a large slope will result in a ratio smaller than 1 giving a negative
value for the logarithm taken.

Has any work been done on this?

Sincerely,

Roderik 




Ludwig M Brinckmann wrote:
> 
> Looking through the code of r.terraflow I discovered that there is one 
> compile time only option that significantly reduces/improves the
> performance 
> of r.terraflow. At the moment builds produce the less performant version
> by 
> default, which for such a long running program is not good. Only those who 
> read and modify the source code can get the faster version.
> 
> options.h, l. 47, #defines OUTPUT_TCI by default, causing additional files 
> generated and in my case a significant (I think millions) number of error 
> messages from this TCI option from sweep.cc line 143 (tci negative).
> 
> Not being a GIS person I have no idea what the error means, the output
> from 
> r.terraflow seemed to correlate with reality despite the message, and even 
> the author of this bit seemed not sure what the error signified: see line 
> 141: is this true?. Printing the error a zillion times added a night to my 
> program run.
> 
> 

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