[GRASS-dev] v.kcv enahncement- was Re: How to calculate mean coordinates from big point datasets?

[Helena Mitasova]

Markus,

when you are at it, can you also have a look at v.kcv?
http://grass.osgeo.org/grass70/manuals/v.kcv.html

I am wondering whether it works efficiently with lidar data sets (millions of points) - I heard that it takes forever,
but that was about a year ago and I haven't tried it myself.
For example, if I want to partition the data set into 1% test points and 99% given data points (for example to test
interpolation) it appears I may need 100 partitions as there is no way to have just two partitions with different size. 

One of the problems may be the table - perhaps if this was run without the table and the output was written into 
two (or k) separate files, it could be faster? The core of the algorithm which is based on finding the closest 
points to the set of random points should allow this.
Creating a subset of points which are farther apart than given threshold (2d or 3d distance) would be also useful
(it is done internally in v.surf.rst and I have a version which does it with 3D distances, but the resulting subset is not
written into output file).

This is not urgent but if it is not too difficult  it would be nice to have,
or let us know if it already works and I just cannot find the right module,

Helena

Helena Mitasova
Associate Professor
Department of Marine, Earth, and Atmospheric Sciences
2800 Faucette Drive, Rm. 1125 Jordan Hall
North Carolina State University
Raleigh, NC 27695-8208
hmitaso at ncsu.edu

"All electronic mail messages in connection with State business which are sent to or received by this account are subject to the NC Public Records Law and may be disclosed to third parties.” 

On Sep 22, 2013, at 11:06 AM, Markus Metz wrote:

> Markus Neteler wrote:
>> Hi,
>> 
>> I came across this question:
>> 
>> http://gis.stackexchange.com/questions/71734/how-to-calculate-mean-coordinates-from-big-point-datasets
> 
> Please try the new addon v.centerpoint [0]. It calculates various
> center points for point clouds, lines, and areas. Standard options are
> the geometric mean (center of gravity) and geometric median (more
> robust for outliers). There are additional options to calculate center
> points for points, lines and areas, explained in the manual. The
> geometric medians (points of minimum distance to all other points) are
> approximations, but fairly accurate and very fast. I would be
> surprised if any other GIS software can calculate these center points.
> 
> Markus M
> 
> [0] http://grasswiki.osgeo.org/wiki/AddOns/GRASS7/vector#v.centerpoint
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