Re: [R-sig-Geo] vgmST parameters

[Dr . Benedikt Gräler]

Admittedly, the choice of the initial parameter is not an easy task. 
Different models combine the components in a different way. In the 
separable model for instance, the spatial and temporal variogram are set 
to a joint sill of 1 each where the sill of the entire variogram is a 
separate parameter. Contrary, the metric covariance model only has a 
single variogram model as input that represents the entire joint sill 
where others are a product or the sum of two or three models (see [1] 
for details). I wrote a shiny app that is available as source from [2] 
and a link to a running instance is listed at [3]. Running the app 
locally for one owns empirical variogram might help to identify the 
right starting values.

HTH,
 Ben

[1] 
https://cran.r-project.org/web/packages/gstat/vignettes/spatio-temporal-kriging.pdf
[2] https://github.com/BenGraeler/copulatheque/tree/master/spacetime
[3] http://ben.graeler.org/shiny-apps/


On 25/09/2017 04:44, Mahsa Sameti wrote:
Dear all

When working with vgmST function, how we choose starting values for space,
time anf joint vgm?
If we should choose them from sample stvariogram, why are they different in
different covariance models? I mean, initial values of space and time vgm in
separable model is different from sum-metric model. how we choose them?

Thanks alot.

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Dr. Benedikt Gräler
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