[GRASS-user] Re: [GRASS-dev] [grass-code R][338] different sampling methods

[Dylan Beaudette]

On Monday 19 March 2007 08:00, grass-coder at wald.intevation.org wrote:
> code R item #338, was opened at 2007-03-19 15:00
> Status: Open
> Priority: 3
> Submitted By: Martin Wegmann (wegmann)
> Assigned to: Nobody (None)
> Summary: different sampling methods
> Issue status: None
> GRASS component: vector
> Operating system: Linux
> Operating system version: debian
>
>
> Initial Comment:
> Hello,
>
> beside v.random or r.random to set points for latter analysis into an area
> other options would be very handy:
>
> - sampling every 10th point of raster
> - linear sampling: small areas have less points than larger areas
>
> other sampling strategies could be implemented see Dylans page:
> http://casoilresource.lawr.ucdavis.edu/drupal/node/320
>
> this ought to be either done per raster or per raster but separated by
> classes in raster.
>
> Martin
>
>

Hi Martin,

I have thought about this as well. I am not a good enough coder to implement 
all of the sampling routines that would be required: i.e. using 
stratification, etc. I have been able to create sampling designs using 
the 'spatstat' package in R however. I see two possible approaches:

1. we implement a full suite of sampling algorithms into v.random
- regular grid
- non-aligned
- random
- random stratified by areas or lines
- random along line segments
- random generation of line segments

this would require some work, but I have some references for most of the 
algorithms handy -- I cannot implement them well.


2. we work with Roger Bivand to create some tutorials on moving grass vectors 
into R, and using the sampling algorithms there, finally moving the results 
back to GRASS. I think that this is currently possible, we just need some 
help writing it up. On the page that you referenced 
(http://casoilresource.lawr.ucdavis.edu/drupal/node/319) I have used 
intermediate text files to move GRASS vectors back and forth. Using the 
spgrass6 package to do this would be a big improvement.

Cheers,


-- 
Dylan Beaudette
Soils and Biogeochemistry Graduate Group
University of California at Davis
530.754.7341