npsp: Nonparametric spatial (geo)statistics

This package implements nonparametric methods which may be useful in geostatistical practice.

Main functions

locpol, np.den and np.svar use local polynomial kernel smoothing to compute nonparametric estimates of a multidimensional regression function (e.g. a spatial trend), a probability density function or a semivariogram (or their first derivatives), respectively. Estimates of these functions can be constructed for any dimension (the amount of available memory is the only limitation). To speed up computations, linear binning is used to discretize the data. A full bandwidth matrix and a multiplicative triweight kernel is used to compute the weights. Main calculations are performed in FORTRAN using the LAPACK library.

np.svariso.corr computes a bias-corrected nonparametric semivariogram estimate using an iterative algorithm similar to that described in Fernandez-Casal and Francisco-Fernandez (2014). This procedure tries to correct the bias due to the direct use of residuals, obtained from a nonparametric estimation of the trend function, in semivariogram estimation.

fitsvar.sb.iso fits a ‘nonparametric’ isotropic Shapiro-Botha variogram model by WLS. Currently, only isotropic semivariogram estimation is supported.

There are also functions for plotting data joint with a legend representing a continuous color scale. splot allows to combine a standard R plot with a legend. spoints, simage and spersp draw the corresponding high-level plot with a legend strip for the color scale. These functions are based on image.plot of package fields.

Among the other functions intended for direct access by the user, the following could be emphasized: binning, bin.den, svar.bin, h.cv and interp. There are also some functions which can be used to interact with other packages. For instance, as.variogram (geoR) or as.vgm (gstat).

Kriging is not yet implemented in this package. Users are encouraged to use krige (or krige.cv) utilities in gstat package together with as.vgm.

Author

Ruben Fernandez-Casal (Dep. Mathematics, University of A Coru~na, Spain). Please send comments, error reports or suggestions to rubenfcasal@gmail.com.

References