[GRASS-dev] Re: [GRASS-user] Maximum number of points for v.what.rast

[Moritz Lennert]

On 02/05/11 12:44, Rebecca Bennett wrote:
> Hi Moritz,
>
> Thanks for responding.
>
>  >Which backend are you using ?
>
> Backend is currently dbf (default). Is there a preferred option for
> speeding up this type of query?

I don't know if there have been any speed tests of backends, but you 
could try with PostgreSQL, making sure that the cat column has an index.

>
>  >Which process is running during all this time ?
>
> Not sure exactly which process is running. I did --verbose but the chat
> stopped after the "excluding x points outside region" message. Any tips
> on how to tell which point it is sticking at would be gratefully received!

Depends on which OS you are on. In GNU/Linux just type 'top' in the 
command line and look at which process is using up CPU time.

>
>  >The module executes each individual update query one at a time. Maybe
> it might be more efficient >to group them into a temporary file with the
> SQL statements and then run that all at once?
>
> Sounds good but I have no idea how to do this - can you point me in the
> direction of some more info so that I could try this method?

This is more on the developers' side, as it will have to be programmed 
in the module.

For now, what you could already try is to work in smaller batches, by 
reducing the number of points using the where clause and/or the region 
you work on (using g.region before v.what.rast).

Moritz