[R-sig-Geo] spatial distance in sum metric spatiotemporal variogram

[Dr. Benedikt Gräler]

Dear Sara,

if you provide information about the coordinate reference system in your 
object lnpm10_stfdf at sp@proj4string (e.g. if your data is recorded as 
WGS84 geographic coordinates: lnpm10_stfdf at sp@proj4string <- 
CRS("+init=epsg:4326") ), distances are calculated as great-circle 
distances in "km" for geographic CRS, as straight line distances in m 
for projected CRS and if no CRS is defined, the distances will be the 
simple euclidean distance of the coordinates.

In your example, there does not seem to be any information about the CRS 
and the values are then euclidean distances between latitudes and 
longitudes (quite miss-leading in most parts of the world, i.e. 1° N-S 
might strongly deviate from 1° E-W).

Furthermore - just to clarify - what you present is the empirical 
spatiotemporal variogram. No assumptions about a model (metric, 
sum-metric, ...) nor any fit of model parameters have been made.

HTH,

  Ben


On 18/10/2017 09:33, sara osama wrote:
> 
> Dear All,
> I have fitted the attached sum-metric variogram using the following command:
> varpm10 <- 
> variogramST(lnpm10only~1,data=lnpm10_stfdf,assumeRegular=F,na.omit=T)
> 
> and the distance in the figure are in decimals. I want to know how this 
> distances are calculated and what is the unit of measurement used. this 
> is the coordinates of the first 5 observations my data
> 
>  > coords
>       longitude latitude
> 1     30.92500 29.95300
> 61    31.36000 30.26000
> 121   31.33300 29.84720
> 181   31.29800 29.90500
> 241   31.20416 30.04278
> 301   31.32000 30.06000
> 361   31.23900 30.09470
> by the way the data consists of only 26 stations where the max distance 
> is about 200 km.
> 
> Any help will be highly appreciated
> 
> Best regards
> Sara
> 
> -- 
> Best Regards
> 
> 	Faculty of Economics & Political Science
> Cairo University
> 
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-- 
Dr. Benedikt Gräler
52°North Initiative for Geospatial Open Source Software GmbH
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