[R-sig-Geo] spatio temporal anisotropy: help with stAni argument

[Barry Rowlingson]

This question has also been posted to gis.stackexchange.com:

https://gis.stackexchange.com/questions/283607/spatio-temporal-anisotropy-in-r-stani-argument-in-vgmst-and-krigest/

and better answers than mine there are welcome...

Barry


On Tue, May 22, 2018 at 8:39 AM, Dr. Benedikt Gräler <b.graeler at 52north.org>
wrote:

> Dear Bruno,
>
> stAni relates spatial and temporal distances to each other in the model
> for the data set under study. A value of 100 km/day reflects that two
> stations 100 km apart have about the same strength of dependence as the
> values one day apart at the same location (This is in general only true for
> at most one pair of spatial and temporal distances and a 'global'
> compromise is sought). The function gstat::estiStAni provides a few
> heuristics to estimate the spatio-temporal anisotropy.
>
> When a spatio-temporal vgm including a metric component is fitted, the
> stAni parameter is optimized under the objective to find the theoretical
> vgm surface that best fits the empirical one.
>
> In krigeST, an additional and approximate stAni parameter can be provided
> to ease the (pre-)selection of the most relevant observations in the
> space-time cube for the prediction when local kriging is carried out. Note
> that the most relevant (i.e. strongest correlated) observations need not to
> form a cube, but depend on the actual vgm-model in use (see also the
> vignette "Spatio-Temporal Interpolation using gstat" at [1]).
>
> The unit of stAni depends on the spatial and temporal units of your data
> set. Check the units of the empirical variogram to find out which units
> R/gstat uses for your data set.
>
> Miss-specifying the stAni parameter will put too large or too small
> weights on the observations with a temporal difference resulting in bad
> predictions (this also holds vise-versa for spatial distances).
>
> HTH,
>
>  Ben
>
> [1] https://cran.r-project.org/web/packages/gstat/vignettes/spat
> io-temporal-kriging.pdf
>
>
> On 21.05.2018 15:16, Bruno Sesti wrote:
>
>> Hi,
>> I have some problems in understanding the usage of argument 'stAni' of
>> vgmST and krigeST functions, for.the setting of spatio temporal
>> anisotropy.
>> How have I to interpret this argument, that is the integer value that I
>> saw
>> I have to assign to it, what does it means?
>> How can this argument influence the result of prediction?
>> Are units of spatial and temporal ranges and lags related to this
>> argument?
>> How can I study the spatio temporal anisotropy of my data?
>> Kind regards.
>>
>>         [[alternative HTML version deleted]]
>>
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>>
> --
> Dr. Benedikt Gräler
> 52°North Initiative for Geospatial Open Source Software GmbH
> Martin-Luther-King-Weg 24
> 48155 Muenster, Germany
>
> E-Mail: b.graeler at 52north.org
> Fon: +49-(0)-251/396371-39
> Fax: +49-(0)-251/396371-11
>
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>
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