On 2007-December-04 , at 21:38 , Scionforbai wrote: >> - krigging in package fields, which also requires irregular spaced >> data > > That kriging requires irregularly spaced data sounds new to me ;) It > cannot be, you misread something (I feel free to say that even if I > never used that package).
Of Krigging I only know the name and general intent so I gladly line up to your opinion. I just read the description in ?Krig in the package fields which says: " Fits a surface to irregularly spaced data. " But there are probably other Krigging methods I overlooked. > It can be tricky doing kriging, though, if you're not comfortable with > a little bit of geostatistics. You have to infer a variogram model for > each data set; you possibly run into non-stationarity or anisotropy, > which are indeed very well treated (maybe at best) by kriging in one > of its forms, but ... it takes more than this list to help you then; > basically kriging requires modelling, so it is often very difficult to > set up an automatic procedure. I can reccomend kriging if the spatial > variability of your data (compared to grid refinement) is quite > important. This was the impression I had too: that Krigging is an art in itself and that it requires you to know much about your data. My problem is simpler: the variability is not very large between grid points (it is oceanic current velocity data so it is highly auto-correlated spatially) and I can get grids fine enough for variability to be low anyway. So it is really purely numerical. > In other simple cases, a wheighted mean using the (squared) inverse of > the distance as wheight and a spherical neighbourhood could be the > simpliest way to perform the interpolation. Yes, that would be largely enough for me. I had C routines for 2D polynomial interpolation of a similar cases and low order polynomes gave good results. I just hoped that R had that already coded somewhere in an handy and generic function rather than having to recode it myself in a probably highly specialized and not reusable manner. Thank you very much for you answer and if someone knows a function doing what is described above, that would be terrific. JiHO --- http://jo.irisson.free.fr/ ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
