[R-sig-Geo] Factorial kriging in GStat - tips for implementation?

[Edzer Pebesma]

On 08/27/2015 02:48 AM, Tim Peterson wrote:
> Hi all,
> 
> I'm looking to undertake factorial colocated cokriging with GStat but
> factorial kriging does not appear to be an available option in GStat (eg
> help.search("factorial kriging") ). There was a post in 2007 requesting
> this feature (http://marc.info/?l=r-sig-geo&m=119810046000747) and a
> proposed approach in 2000
> (https://www.mail-archive.com/gstat-info@geog.uu.nl/msg00045.html) but
> no updates since. As far as I can tell, the required changes would be to
> 'gls.c' lines 412-423, specifically the call to GCV0 for calculating C0
> (right-hand side of the kriging matrix) should be edited so that only
> the covariance for the required factor is calculated.

Not being an expert in factorial kriging, I also think that this is what
is needed. A challenge may be to make the implementation simple and
clean, both from the perspective of the user as well as from the code
maintainer.

If the only goal is to suppress the nugget effect, as the poster in your
first link mentions, try replacing a "Nug" variogram model with an "Err"
variogram model.

> 
> Anyway, before I consider adding this feature to GStat, I'd be grateful
> if anyone could share tips or thoughts. Lastly, any changes I make will
> (of course) be freely shared.
> 
> Many thanks,
> 
> Tim
> 
> ----------------------
> Dr. Tim Peterson
> 
> The Department of Infrastructure Engineering
> The University of Melbourne, 3010 Australia
> T: +61 3 8344 9950, M: +61 0438 385 937
> 
> Dept. profile :
> http://www.ie.unimelb.edu.au/people/staff.php?person_ID=141135
> Research Gate : https://www.researchgate.net/profile/Tim_Peterson7
> Google Scholar:
> http://scholar.google.com.au/citations?user=kkYJLF4AAAAJ&hl=en&oi=ao
> 
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-- 
Edzer Pebesma
Institute for Geoinformatics (ifgi),  University of Münster,
Heisenbergstraße 2, 48149 Münster, Germany; +49 251 83 33081
Journal of Statistical Software:   http://www.jstatsoft.org/
Computers & Geosciences:   http://elsevier.com/locate/cageo/
Spatial Statistics Society http://www.spatialstatistics.info

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