[gdal-dev] weeding out x,y,z points

Wesley Roberts wroberts at csir.co.za
Thu Feb 26 02:59:10 EST 2009

Have you looked at the spatial applications available in R. It sounds like you have a lidar data set yes? R has a bunch of packages that could help, gstat, spatstat, maptools, sp, etc have a look at 


One option I can think of, but cant remember how to do it is the following. Sometimes when interpolating lidar points (or any for that matter) it is useful to remove some points from your data for validation later on. typically one would remove 5 or 10% of the data and use this to validate the final surface. So you would then sit with the modelling data containing 90% of the original data and your validation data containing 10% of the original data. The removal is usually done randomly and would therefore allow you to retain the structure of your original data.

As I said earlier I cant exactly remember how this is done, but the link should give you a good start.


Wesley Roberts MSc.
Researcher: Earth Observation (Ecosystems)
Natural Resources and the Environment
Tel: +27 (21) 888-2490
Fax: +27 (21) 888-2693

"To know the road ahead, ask those coming back."
- Chinese proverb

>>> <nicholas.g.lawrence at mainroads.qld.gov.au> 02/26/09 6:57 AM >>>
> nicholas.g.lawrence at mainroads.qld.gov.au wrote:
> > A client has a very large (millions of records) ascii file consisting
> > solely of x,y,z co-ordinates.
> >
> > They would like to reduce the number of records by weeking out points
> > are too close to each other.
> >
> > Can GDAL or OGR weed out 3D points based on proximity to each other?

> A job for GMT's blockmean or blockmedian.

> Joaquim Luis

Okay, I downloaded the Manpages.

My initial reading is that blockmean and blockmedian work by averaging
the values.

My client says that they want the resulting data points to be
a subset of the original data points, that is the process should
delete points, not re-calculate new ones that are an average.

Is this still do-able? Is there a specific option I should
be looking at?


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