[R-sig-Geo] decimate points from a Lidar file

[Dylan Beaudette]

On Tuesday 08 September 2009, Michael Denslow wrote:
> Dear R-sig-geo,
>
> I am posting the following question for one of my professors. I would
> appreciate it if you could help me point him in the right direction.
>
> He is looking for a function which could take a lidar point shapefile
> and decimate (remove) a selected number of points
> from the file. Below is what he asked me. The file of the merged LIDAR
> tiles contains roughly 350,000,000 points.
>
> "I am looking for some software to take a shapefile of lidar elevation
> points and remove a selected number of points. The shapefile
> (with fewer points) would then be used to generate a DEM. A
> calculation of the appropriate resolution for a DEM can be made based
> on a relationship between the
> number of points and extent of the study area. The goal is to create
> DEMs at a series of resolutions with the appropriate points to area
> relationship. So a
> software program with which you could remove a selected number of
> lidar points would be helpful."
>
> I imagine that one of the packages that deals with point data (e.g.
> sp, spatstat) can do this kind of thing but I am not sure how to get
> him started. Can anyone point me to a specify function or make a
> suggestion.
>
> Thanks in advance,
> Michael

Hi,

I would recommend the r.in.xyz command within GRASS GIS. It can be used for 
operations very similar to what you are looking for. The resulting file is a 
raster, decimated to some set resolution. Some screen shots:

http://hamish.bowman.googlepages.com/grassfiles#xyz

Cheers,
Dylan

-- 
Dylan Beaudette
Soil Resource Laboratory
http://casoilresource.lawr.ucdavis.edu/
University of California at Davis
530.754.7341