<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <title>GRASS GIS: r.surf.idw2</title> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> <link rel="stylesheet" href="grassdocs.css" type="text/css"> </head> <body bgcolor="white"> <img src="grass_logo.png" alt="GRASS logo"><hr align=center size=6 noshade> <h2>NAME</h2> <em><b>r.surf.idw2</b></em> - Surface generation program. <h2>KEYWORDS</h2> raster <h2>SYNOPSIS</h2> <b>r.surf.idw2</b><br> <b>r.surf.idw2 help</b><br> <b>r.surf.idw2</b> <b>input</b>=<em>name</em> <b>output</b>=<em>name</em> [<b>npoints</b>=<em>count</em>] [--<b>overwrite</b>] [--<b>verbose</b>] [--<b>quiet</b>] <h3>Flags:</h3> <DL> <DT><b>--overwrite</b></DT> <DD>Allow output files to overwrite existing files</DD> <DT><b>--verbose</b></DT> <DD>Verbose module output</DD> <DT><b>--quiet</b></DT> <DD>Quiet module output</DD> </DL> <h3>Parameters:</h3> <DL> <DT><b>input</b>=<em>name</em></DT> <DD>Name of input raster map</DD> <DT><b>output</b>=<em>name</em></DT> <DD>Name for output raster map</DD> <DT><b>npoints</b>=<em>count</em></DT> <DD>Number of interpolation points</DD> <DD>Default: <em>12</em></DD> </DL> <H2>DESCRIPTION</H2> <EM>r.surf.idw2</EM> fills a raster matrix with interpolated values generated from a set of irregularly spaced data points using numerical approximation (weighted averaging) techniques. The interpolated value of a cell is determined by values of nearby data points and the distance of the cell from those input points. In comparison with other methods, numerical approximation allows representation of more complex surfaces (particularly those with anomalous features), restricts the spatial influence of any errors, and generates the interpolated surface from the data points. It is the most appropriate method to apply to most spatial data. The <B>npoints</B> parameter defines the number of points to use for interpolation. The default is to use the 12 nearest points when interpolating the value for a particular cell. <H2>NOTES</H2> The amount of memory used by this program is related to the number of non-zero data values in the input map layer. If the input raster map layer is very dense (i.e., contains many non-zero data points), the program may not be able to get all the memory it needs from the system. The time required to execute increases with the number of input data points. <P> If the user has a mask set, then interpolation is only done for those cells that fall within the mask. However, all non-zero data points in the input layer are used even if they fall outside the mask. <P> This program does not work with latitude/longitude data bases. Another surface generation program, named <EM><A HREF="r.surf.idw.html">r.surf.idw</A></EM>, should be used with latitude/longitude data bases. <P> The user should refer to the manual entries for <br> <EM><A HREF="r.surf.idw.html">r.surf.idw</A></EM><br> <EM><A HREF="r.surf.contour.html">r.surf.contour</A></EM><br> <EM><A HREF="v.surf.rst.html">v.surf.rst</A></EM> <br>to compare this surface generation program with others available in GRASS. <H2>SEE ALSO</H2> <EM><A HREF="r.surf.contour.html">r.surf.contour</A></EM>, <EM><A HREF="r.surf.idw.html">r.surf.idw</A></EM>, <EM><A HREF="r.surf.gauss.html">r.surf.gauss</A></EM>, <EM><A HREF="r.surf.fractal.html">r.surf.fractal</A></EM>, <EM><A HREF="r.surf.random.html">r.surf.random</A></EM>, <EM><A HREF="r.surf.idw2.html">r.surf.idw2</A></EM>, <EM><A HREF="v.surf.rst.html">v.surf.rst</A></EM> <H2>AUTHOR</H2> Michael Shapiro, U.S.Army Construction Engineering Research Laboratory <p><i>Last changed: $Date: 2006-04-13 21:01:38 +0200 (Thu, 13 Apr 2006) $</i> <HR> <P><a href="index.html">Main index</a> - <a href="raster.html">raster index</a> - <a href="full_index.html">Full index</a></P> <P>© 2003-2008 <a href="http://grass.osgeo.org">GRASS Development Team</a></p> </body> </html>
