GRASS GIS manual: v.surf.nnbathy

NAME

v.surf.nnbathy - Interpolates a raster map using the nnbathy natural neighbor interpolation program.

KEYWORDS

vector, surface, interpolation, natural, neighbor

SYNOPSIS

v.surf.nnbathy

v.surf.nnbathy --help

v.surf.nnbathy [input=name] [layer=string] [file=name] output=name [column=name] [where=sql_query] [algorithm=string] [--overwrite] [--help] [--verbose] [--quiet] [--ui]

Flags:

--overwrite: Allow output files to overwrite existing files
--help: Print usage summary
--verbose: Verbose module output
--quiet: Quiet module output
--ui: Force launching GUI dialog

Parameters:

input=name: Name of input vector map; Name of input vector points map
layer=string: Layer number; If set to 0, z coordinates are used. (3D vector only); Default: 1
file=name: Containing x,y,z data as three space separated columns
output=name [required]: Name of output raster map
column=name: Name of the attribute column with values to be used for approximation (if layer>0)
where=sql_query: WHERE conditions of SQL statement without 'where' keyword; Example: income < 1000 and population >= 10000
algorithm=string: Settings; Options: l, nn, ns; Default: nn; l: Linear; nn: Sibson natural neighbor; ns: Non-Sibsonian natural neighbor

DESCRIPTION
NOTES
EXAMPLE
REQUIREMENTS
SEE ALSO
AUTHOR

DESCRIPTION

v.surf.nnbathy is an interface between the external nnbathy utility and GRASS. nnbathy is a surface interpolation program provided with nn - a natural neighbor interpolation library, written by Pavel Sakov.

v.surf.nnbathy provides 3 interpolation algorithms. According to nn library documentation these are: Delaunay interpolation (alg=l), Watson's algortithm for Sibson natural neighbor interpolation (alg=nn) and Belikov and Semenov's algorithm for non-Sibsonian natural neighbor interpolation (alg=ns). For performing the underlaying Delaunay triangulation in all cases nnbathy uses triangle software by Jonathan Richard Shewchuk.

The output raster map is a continous surface interpolated from the input or file data.

NOTES

nnbathy, if built with '-DNN_SERIAL' (default as of nn 1.85), is able to create a grid of virtually any size. It interpolates and writes one output point at a time only. This eliminates the necessity to hold the whole output array in memory. However, even then all the input points are still held in the memory.

Requires GRASS 7 and nnbathy 1.76 or greater.
Build nnbathy according to instructions provided with its source code and put it somewhere in your $PATH.
The output raster map extent and resolution match the region settings at which the script was started.
The output raster map non-NULL area is limited to the convex hull encompassing all the non-NULL input cells.
The output is double precision floating point raster map (DCELL).
Natural neighbor is a an exact interpolation algorithm, so all non-NULL input points have their value exactly preserved in the output.
There is circa 0.2 KB memory overhead per each input cell. However, the output grid can be of any size, if nnbathy is built with -DNN_SERIAL switch.
v.surf.nnbathy creates 4 temporary files: ASCII x,y,z lists of the input points and output cells, and the output list converted into GRASS ASCII format. Then it makes a GRASS raster map from the latter - and only then it removes the 3 temp files, when the script terminates. Thus, at the script run time several times more disk space might be required, than the final GRASS raster map would actually occupy.

EXAMPLE

g.region raster=elevationelev_lid792_randpts@PERMANENT -p 
v.surf.nnbathy input=elevation_lid792_randpts@PERMANENT output=raster_map column=value 
d.rast map=raster_map

REQUIREMENTS

nnbathy library by Pavel Sakov

AUTHOR

Adam Laza, OSGeoREL, Czech Technical University in Prague (mentor: Martin Landa) Corrected by Roberto Marzocchi, roberto.marzocchi@gter.it

Based on v.surf.nnbathy from GRASS 6 by:
Hamish Bowman, Otago University, New Zealand
Based on r.surf.nnbathy by Maciej Sieczka

Last changed: $Date: 2018-04-03 12:43:37 +0200 (Tue, 03 Apr 2018) $

SOURCE CODE

Available at: v.surf.nnbathy source code (history)