# spatial modelling projection question

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## spatial modelling projection question

 Hi - I do some spatial modeling over the inter-mountain west of USA and am wondering about projections.  Most people suggest longlat is not  a proper 'projection' for geostatistics and in fact some packages require a projection with meters instead of degrees. I believe gstat will compute great circle distances for longlat data. I have seen some caveats on this, e.g. "there are no checks that the variogram model can be applied sanely on a sphere" . The standard projection for a domain my size/geographic location seems to be the conus albers from USGS (epsg:5070) which is an equal area projection so my question is: Wouldn't it make more sense to do spatial modeling with a true distance projection, i.e. longlat, than an equal area projection for which distances are skewed? What makes the variogram model potentially inappropriate on a sphere (overlooking the fact that the earth isn't really a sphere)? I appreciate your help understanding this. Thanks Dominik         [[alternative HTML version deleted]] _______________________________________________ R-sig-Geo mailing list [hidden email] https://stat.ethz.ch/mailman/listinfo/r-sig-geo
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## Re: spatial modelling projection question

 On 05/13/2014 08:19 PM, Dominik Schneider wrote: > so my question is: Wouldn't it make more sense to do spatial modeling with > a true distance projection, i.e. longlat, than an equal area projection for > which distances are skewed? What makes the variogram model potentially I would say yes, but haven't given it much thought. > inappropriate on a sphere (overlooking the fact that the earth isn't really > a sphere)? Some variogram models are not positive definite (or semi-negative definite) in some spaces; linear-with-sill is only valid in 1 D, circular only in 2D, spherical only in 3D. Spheres, or ellipsoides, are another thing when measuring surface lines. See also http://dx.doi.org/10.1007/s11004-011-9344-7-- Edzer Pebesma Institute for Geoinformatics (ifgi), University of Münster Heisenbergstraße 2, 48149 Münster, Germany. Phone: +49 251 83 33081 http://ifgi.uni-muenster.de GPG key ID 0xAC227795 _______________________________________________ R-sig-Geo mailing list [hidden email] https://stat.ethz.ch/mailman/listinfo/r-sig-geo signature.asc (501 bytes) Download Attachment
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