Kosher to krig in Lat-Lon?

[Ashton Shortridge <ashton@geog.ucsb.edu>]

As a followup, I'm not certain you'll get good results interpolating in
lat-lon. In ground units of distance decimal degrees (or seconds) vary,
and certainly differ tremendously at higher latitudes in the east-west
and north south directions.

I'm not certain that separating the variogram into north-sourth and
east-west components will account for this difference. If it were my
data, I'd project it to something using standard distance units like
meters or kilometers and do the interpolation in that.

Ashton Shortridge

Edzer Pebesma wrote:

> The `V' field (location-specific measurement errors) works for
> data for which the variogram of measurement error-free values
> were used to model the variogram.
>
> Non-constant measurement errors implies that your data are
> non-stationary (w.r.t. variance). If there is little variation
> in the measurement errors, you can model their average behaviour
> with a nugget effect. If there is large variation, it will be
> hard to derive the underlying variogram from them.
>
> So, if you modelled the variogram from the data assuming constant
> measurement error, and then you add it (using `V' field) later on,
> you're accounting for it twice.
> --
> Edzer