.TH r.resamp.interp 1grass "" "GRASS 8.3.1" "GRASS GIS User's Manual"
.SH NAME
\fI\fBr.resamp.interp\fR\fR  \- Resamples raster map to a finer grid using interpolation.
.SH KEYWORDS
raster, resample, interpolation, nearest neighbor, bilinear, bicubic, lanczos, parallel
.SH SYNOPSIS
\fBr.resamp.interp\fR
.br
\fBr.resamp.interp \-\-help\fR
.br
\fBr.resamp.interp\fR \fBinput\fR=\fIname\fR \fBoutput\fR=\fIname\fR  [\fBmethod\fR=\fIstring\fR]   [\fBnprocs\fR=\fIinteger\fR]   [\fBmemory\fR=\fImemory in MB\fR]   [\-\-\fBoverwrite\fR]  [\-\-\fBhelp\fR]  [\-\-\fBverbose\fR]  [\-\-\fBquiet\fR]  [\-\-\fBui\fR]
.SS Flags:
.IP "\fB\-\-overwrite\fR" 4m
.br
Allow output files to overwrite existing files
.IP "\fB\-\-help\fR" 4m
.br
Print usage summary
.IP "\fB\-\-verbose\fR" 4m
.br
Verbose module output
.IP "\fB\-\-quiet\fR" 4m
.br
Quiet module output
.IP "\fB\-\-ui\fR" 4m
.br
Force launching GUI dialog
.SS Parameters:
.IP "\fBinput\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of input raster map
.IP "\fBoutput\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name for output raster map
.IP "\fBmethod\fR=\fIstring\fR" 4m
.br
Sampling interpolation method
.br
Options: \fInearest, bilinear, bicubic, lanczos\fR
.br
Default: \fIbilinear\fR
.br
\fBnearest\fR: Nearest\-neighbor interpolation
.br
\fBbilinear\fR: Bilinear interpolation
.br
\fBbicubic\fR: Bicubic interpolation
.IP "\fBnprocs\fR=\fIinteger\fR" 4m
.br
Number of threads for parallel computing
.br
Default: \fI1\fR
.IP "\fBmemory\fR=\fImemory in MB\fR" 4m
.br
Maximum memory to be used (in MB)
.br
Cache size for raster rows
.br
Default: \fI300\fR
.SH DESCRIPTION
\fIr.resamp.interp\fR resamples an input raster map by interpolating between
the neighboring cells via a selectable resampling algorithm. All cells
present in the neighborhood of the input raster cell must be non\-null to
generate a non\-null cell in the output raster map. A choice of four
interpolation methods is available; each uses the weighted values of a different
number of adjacent cells in the input map to determine the value of each
cell in the output map as follows:
.RS 4n
.IP \(bu 4n
nearest neighbour (1 cell)
.IP \(bu 4n
bilinear (4 cells)
.IP \(bu 4n
bicubic (16 cells)
.IP \(bu 4n
lanczos (25 cells)
.RE
.PP
This module is intended for reinterpolation of continuous data
to a different resolution rather than for interpolation from scattered data
(use the \fIv.surf.*\fR modules for that purpose).
.SH NOTES
.PP
Resampling modules (\fIr.resample, r.resamp.stats, r.resamp.interp,
r.resamp.rst\fR) resample the map to match the current region settings.
.PP
Note that for bilinear, bicubic and lanczos interpolation,
cells of the output raster that cannot be bounded by the appropriate number
of input cell centers are set to NULL (NULL propagation). This could occur
due to the input cells being outside the current region, being NULL or MASKed.
.PP
For longitude\-latitude locations, the interpolation algorithm is based on
degree fractions, not on the absolute distances between cell centers.  Any
attempt to implement the latter would violate the integrity of the
interpolation method.
.SS PERFORMANCE
.PP
By specifying the number of parallel processes with \fBnprocs\fR option,
\fIr.resamp.interp\fR can run significantly faster, see benchmarks below.
.br
\fIFigure: Benchmark shows execution time for different
number of cells. See benchmark scripts in source code.\fR
.PP
To reduce the memory requirements to minimum, set option \fBmemory\fR to zero.
To take advantage of the parallelization, GRASS GIS
needs to compiled with OpenMP enabled.
.SH EXAMPLE
Resample elevation raster map to a higher resolution (from 500m to 250m;
North Carolina sample dataset):
.br
.nf
\fC
g.region raster=elev_state_500m \-p
g.region res=250 \-ap
r.resamp.interp input=elev_state_500m output=elev_state_250m \(rs
                method=bilinear
\fR
.fi
.br
Original 500m resolution elevation map
.PP
.br
Resampled (bilinear) 250m resolution elevation map
.SH SEE ALSO
\fI
g.region,
r.resample,
r.resamp.filter,
r.resamp.rst,
r.resamp.stats
\fR
.PP
Overview: Interpolation and Resampling in GRASS GIS
.SH AUTHOR
Glynn Clements
.SH SOURCE CODE
.PP
Available at:
r.resamp.interp source code
(history)
.PP
Accessed: Sunday Dec 17 17:21:57 2023
.PP
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.PP
© 2003\-2023
GRASS Development Team,
GRASS GIS 8.3.1 Reference Manual