[R-sig-Geo] units for spatial range in stvariogram gstat

[sara osama]

Dear Prof. Pebesma,

Thanks for reply I will try to make it  more clear

the coordinates are converted to decimal degree format using the equation
DD = d + (min/60) + (sec/3600)

and then projected using

> llCRS <- CRS("+proj=longlat +ellps=WGS84")
> pm10_sp <- SpatialPoints(coords, proj4string = llCRS)
> pm10_sp

SpatialPoints:
     longitude latitude
1     30.92500 29.95300
61    31.36000 30.26000
 and the variogram is fitted using

>> varpm10 <- variogramST(lnpm10only~1,data=lnpm10_stfdf,cutoff=0.8,
assumeRegular=T,na.omit=T)

>> sumMetric <- vgmST("sumMetric", space = vgm(psill=5,"Mat", range=50,
nugget=0),time = vgm(psill=500,"Mat", range=50, nugget=0,kappa=0.3), joint
= vgm(psill=10,"Mat", range=100, nugget=1), stAni=200)

>> sumMetric_Vgm <- fit.StVariogram(varpm10, sumMetric,
method="L-BFGS-B",lower=pars.l,upper=pars.u)

*the s.range parameter extracted was 50.6 but if you take a look on  the
figure attached the largest distance on the x-axis is 0.6 ??????*

*so i think the unit on the figure is not the unit of the extracted
parameter. *

by the way the largest ditance between any points in my data set is
approximately 190 km


Thanks again




On Wed, May 17, 2017 at 10:08 PM, Edzer Pebesma <
edzer.pebesma at uni-muenster.de> wrote:

> Your email is not nearly enough for a reader to figure out what you did.
> However, if your data are long/lat, and you instructed gstat about that
> (i.e., proj4string(pm10_sp) indicates coordinates are degrees) then
> gstat computes and returns distances in km.
>
> On 17/05/17 20:56, sara osama wrote:
> >
> > Dear All,
> > I have question concerning the unit of measurement for the range
> > parameter in the fit.stvariogram in gstat, i have fitted the following
> > spatio temporal variogram for data on monthly averages pf pm10 and the
> > longitude and latitude are in decimel format
> >
> >> pm10_sp
> > SpatialPoints:
> >      longitude latitude
> > 1     30.92500 29.95300
> > 61    31.36000 30.26000
> > 121   31.33300 29.84720
> >  and this is the commands for fitting the variogram
> >> varpm10 <- variogramST(lnpm10only~1,data=lnpm10_stfdf,cutoff=0.8,
> assumeRegular=T,na.omit=T)
> >> plot(varpm10,map=F)
> >> sumMetric <- vgmST("sumMetric", space = vgm(psill=5,"Mat", range=50,
> nugget=0),time = vgm(psill=500,"Mat", range=50, nugget=0,kappa=0.3), joint
> = vgm(psill=10,"Mat", range=100, nugget=1), stAni=200)
> >> sumMetric_Vgm <- fit.StVariogram(varpm10, sumMetric,
> method="L-BFGS-B",lower=pars.l,upper=pars.u)
> >> plot(varpm10,sumMetric_Vgm,map=F)
> >
> >> extractPar(sumMetric_Vgm)
> >       sill.s      range.s     nugget.s       sill.t      range.t
> > nugget.t
> >   1.73598444  50.63845035   0.03212857   0.01570379  49.99811448
> > 0.00000000
> >      sill.st <http://sill.st>     range.st <http://range.st>
> > nugget.st <http://nugget.st>         anis
> >   0.00000000 100.00004052   0.09151787 200.00000000
> >
> > --
> > now i want to know the units for these parameters in order to be able to
> > interpret it for example is it in km or m.
> >
> > I really appreciate any help that I deeply need
> >
> > Best Regards
> > Sara
> >
> >       Faculty of Economics & Political Science
> > Cairo University
> >
> >
> > Tel:(202)35728055-(202)35728116-(202)35736608-(202)35736605
> > Fax:(202)35711020
> > Follow us on twitter:https://twitter.com/fepsnews
> >
> >
> > _______________________________________________
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> > R-sig-Geo at r-project.org
> > https://stat.ethz.ch/mailman/listinfo/r-sig-geo
> >
>
> --
> Edzer Pebesma
> Institute for Geoinformatics  (ifgi),  University of Münster
> Heisenbergstraße 2, 48149 Münster, Germany; +49 251 83 33081
> Journal of Statistical Software:   http://www.jstatsoft.org/
> Computers & Geosciences:   http://elsevier.com/locate/cageo/
>
>
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>



-- 
Best Regards

Faculty of Economics & Political Science
Cairo University
Tel:(202)35728055-(202)35728116-(202)35736608-(202)35736605
Fax:(202)35711020
Follow us on twitter:https://twitter.com/fepsnews

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