AI-GEOSTATS: transformation of data

2002-04-09 Thread Sibylle Eisenberger
I´m doing my diploma thesis on the spatial distribution of weeds and I´m an absolute beginner with geostatistics. Please take that into account when reading my question. My data are weed counts with excess zeros and fit a negative binomial distribution. But as far as I know semivariagram

Re: AI-GEOSTATS: Generating skewed distributions

2002-04-09 Thread Edzer J. Pebesma
Yes. Generate a Gaussian random field, add a deterministic trend surface, and take the exponent or a power transform of the sum. -- Edzer William Thayer wrote: I am interested in comparing different estimators of spatial means. Any suggestions or approaches on how to generate a 2-D,

Re: AI-GEOSTATS: transformation of data

2002-04-09 Thread Edzer J. Pebesma
Dear Sibylle, I suspect your residuals will never become normal, because your data are counts. Luckily, normality is not a requirement for variogram calculation nor for kriging interpolation. However, before calculating variograms it may be a good idea to correct for non-stationarity in the

AI-GEOSTATS: Dealing with Universal Kriging

2002-04-09 Thread Rubens Caldeira Monteiro
Dear all, We are trying to apply Universal Kriging to High Plains Aquifer in Kansas (OLEA, 1999) for land surface elevation (LSE), using its 317 data points. The purpose of this application is just for didactic ends. Our first step was to filter a prominent 1st degree drift. The way we

Re: AI-GEOSTATS: Dealing with Universal Kriging

2002-04-09 Thread Isobel Clark
Rubens Your approach has been long used in hydrology and similar fields with much success. The problem with the standard deviation is that it does not include the the 'error' on the estimation of the true drift. To get a composite error you would either have to (a) add your kriging variance