<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"> <!--Converted with LaTeX2HTML 98.1p1 release (March 2nd, 1998) originally by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds * revised and updated by: Marcus Hennecke, Ross Moore, Herb Swan * with significant contributions from: Jens Lippmann, Marek Rouchal, Martin Wilck and others --> <HTML> <HEAD> <TITLE>Rebinning and Interpolation</TITLE> <META NAME="description" CONTENT="Rebinning and Interpolation"> <META NAME="keywords" CONTENT="vol2"> <META NAME="resource-type" CONTENT="document"> <META NAME="distribution" CONTENT="global"> <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"> <LINK REL="STYLESHEET" HREF="vol2.css"> <LINK REL="next" HREF="node138.html"> <LINK REL="previous" HREF="node136.html"> <LINK REL="up" HREF="node136.html"> <LINK REL="next" HREF="node138.html"> </HEAD> <BODY > <!--Navigation Panel--> <A NAME="tex2html3150" HREF="node138.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="icons.gif/next_motif.gif"></A> <A NAME="tex2html3147" HREF="node136.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="icons.gif/up_motif.gif"></A> <A NAME="tex2html3141" HREF="node136.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="icons.gif/previous_motif.gif"></A> <A NAME="tex2html3149" HREF="node1.html"> <IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents" SRC="icons.gif/contents_motif.gif"></A> <BR> <B> Next:</B> <A NAME="tex2html3151" HREF="node138.html">Normalization and Fitting</A> <B> Up:</B> <A NAME="tex2html3148" HREF="node136.html">Spectral Analysis</A> <B> Previous:</B> <A NAME="tex2html3142" HREF="node136.html">Spectral Analysis</A> <BR> <BR> <!--End of Navigation Panel--> <H2><A NAME="SECTION001061000000000000000"> Rebinning and Interpolation</A> </H2> Raw spectra are usually not sampled at constant wavelength or frequency steps, and sometimes even with gaps in between the bins. At some stage the independent variable will have to be converted into linear or non-linear functions of wavelength or frequency units and gaps will have to be filled with interpolated values. Frequent cases are: wavelength calibration, redshift correction, <!-- MATH: $\log(F_\lambda)$ --> <IMG WIDTH="30" HEIGHT="44" ALIGN="MIDDLE" BORDER="0" SRC="img262.gif" ALT="$ \log(F_\lambda)$"> versus <!-- MATH: $\log(\lambda)$ --> <IMG WIDTH="19" HEIGHT="42" ALIGN="MIDDLE" BORDER="0" SRC="img263.gif" ALT="$\log(\lambda)$"> presentation, and the comparison of narrow-band filter spectrophotometry with scanner data. Related commands are <TT>REBIN/LONG</TT>, already described, <TT>REBIN/LINEAR</TT> for linear rebinning, i.e. scale and offset change, <TT>REBIN/II (IT,TI,TT)</TT> to do nonlinear rebin conserving flux (see below) and <TT>CONVERT/TABLE</TT> to interpolate table data into image data. <P> Note that in our implementation we make a conceptual difference between straightforward interpolation and rebinning. <TT>REBIN/II (IT, TI, TT)</TT> redistributes intensity from one sampling domain into another. There is no interpolation across undefined gaps and no extrapolation at the extremities of the input data. If you need these, you will have to manipulate the input data first (generating non-existent information !). <TT>REBIN/II (IT, TI, TT)</TT> conserves flux locally and globally. <P> <BR><HR> <ADDRESS> <I>Petra Nass</I> <BR><I>1999-06-15</I> </ADDRESS> </BODY> </HTML>
