rsaga.inverse.distance: Spatial Interpolation Methods

In RSAGA: SAGA Geoprocessing and Terrain Analysis

Spatial Interpolation Methods

Description

Spatial interpolation of point data using inverse distance to a power (inverse distance weighting, IDW), nearest neighbors, or modified quadratic shephard.

Usage

rsaga.inverse.distance(
  in.shapefile,
  out.grid,
  field,
  power = 1,
  maxdist,
  nmax = 100,
  target,
  env = rsaga.env(),
  ...
)

rsaga.nearest.neighbour(
  in.shapefile,
  out.grid,
  field,
  target,
  env = rsaga.env(),
  ...
)

rsaga.modified.quadratic.shephard(
  in.shapefile,
  out.grid,
  field,
  quadratic.neighbors = 13,
  weighting.neighbors = 19,
  target,
  env = rsaga.env(),
  ...
)

rsaga.triangulation(
  in.shapefile,
  out.grid,
  field,
  target,
  env = rsaga.env(),
  ...
)

Arguments

in.shapefile	Input: point shapefile (default extension: .shp).
out.grid	Output: filename for interpolated grid (SAGA grid file). Existing files will be overwritten!
field	numeric or character: number or name of attribute in the shapefile's attribute table to be interpolated; the first attribute is represented by a zero.
power	numeric (>0): exponent used in inverse distance weighting (usually 1 or 2)
maxdist	numeric: maximum distance of points to be used for inverse distance interpolation (search radius); no search radius is applied when this argument is missing or equals Inf
nmax	Maximum number of nearest points to be used for interpolation; nmax=Inf is a valid value (no upper limit)
target	required argument of type list: parameters identifying the target area, e.g. the x/y extent and cellsize, or name of a reference grid; see rsaga.target().
env	RSAGA geoprocessing environment created by rsaga.env(), required because module(s) depend(s) on SAGA version
...	Optional arguments to be passed to rsaga.geoprocessor(), including the env RSAGA geoprocessing environment.
quadratic.neighbors	integer >=5; default 13.
weighting.neighbors	integer >=3; default 19.

Details

These functions use modules from the grid_gridding SAGA GIS library. They do not support SAGA GIS 2.0.4, which differs in some argument names and parameterizations. Target grid parameterization by grid file name currently doesn't work with SAGA GIS 2.1.0 Release Candidate 1 (see also rsaga.target()); stay tuned for future updates and fixes.

Note

The 'Inverse Distance Weighted' module of SAGA GIS not only support inverse-distance weighted interpolation, but also exponential and other weighting schemes (command line argument WEIGHTING); these are however not accessible through this function, but only through the rsaga.geoprocessor, if needed. See rsaga.get.usage("grid_gridding","Inverse Distance Weighted") for details.

See the example section in the help file for shapefiles::write.shapefile() in package shapefiles to learn how to apply these interpolation functions to a shapefile exported from a data.frame.

Modified Quadratic Shephard method: based on module 660 in TOMS (see references).

Author(s)

Alexander Brenning (R interface), Andre Ringeler and Olaf Conrad (SAGA modules)

References

QSHEP2D: Fortran routines implementing the Quadratic Shepard method for bivariate interpolation of scattered data (see R. J. Renka, ACM TOMS 14 (1988) pp.149-150). Classes: E2b. Interpolation of scattered, non-gridded multivariate data.

See Also

rsaga.target(); gstat::idw() in package gstat.

RSAGA documentation built on Dec. 10, 2022, 1:12 a.m.