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Import.
| author | Daniele Nicolodi <nicolodi@science.unitn.it> |
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| date | Wed, 23 Nov 2011 19:22:13 +0100 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/m-toolbox/html_help/help/ug/ltpda_training_topic_2_1.html Wed Nov 23 19:22:13 2011 +0100 @@ -0,0 +1,151 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" + "http://www.w3.org/TR/1999/REC-html401-19991224/loose.dtd"> + +<html lang="en"> +<head> + <meta name="generator" content= + "HTML Tidy for Mac OS X (vers 1st December 2004), see www.w3.org"> + <meta http-equiv="Content-Type" content= + "text/html; charset=us-ascii"> + + <title>Downsampling a time-series AO (LTPDA Toolbox)</title> + <link rel="stylesheet" href="docstyle.css" type="text/css"> + <meta name="generator" content="DocBook XSL Stylesheets V1.52.2"> + <meta name="description" content= + "Presents an overview of the features, system requirements, and starting the toolbox."> + </head> + +<body> + <a name="top_of_page" id="top_of_page"></a> + + <p style="font-size:1px;"> </p> + + <table class="nav" summary="Navigation aid" border="0" width= + "100%" cellpadding="0" cellspacing="0"> + <tr> + <td valign="baseline"><b>LTPDA Toolbox</b></td><td><a href="../helptoc.html">contents</a></td> + + <td valign="baseline" align="right"><a href= + "ltpda_training_topic_2.html"><img src="b_prev.gif" border="0" align= + "bottom" alt="Topic 2 - Pre-processing of data"></a> <a href= + "ltpda_training_topic_2_2.html"><img src="b_next.gif" border="0" align= + "bottom" alt="Upsampling a time-series AO"></a></td> + </tr> + </table> + + <h1 class="title"><a name="f3-12899" id="f3-12899"></a>Downsampling a time-series AO</h1> + <hr> + + <p> + +Downsampling reduces the sampling rate of the input AOs by an integer factor, which can be very useful for example to reduce data load. + +<p>The <tt>downsample</tt> method takes the following parameters: + <table cellspacing="0" class="body" cellpadding="2" border="0" width="80%"> + <colgroup> + <col width="25%"/> + <col width="75%"/> + </colgroup> + <thead> + <tr valign="top"> + <th class="categorylist">Key</th> + <th class="categorylist">Description</th> + </tr> + </thead> + <tbody> + <!-- Key 'factor' --> + <tr valign="top"> + <td bgcolor="#f3f4f5"> + <p><tt>FACTOR</tt></p> + </td> + <td bgcolor="#f3f4f5"> + <p>The decimation factor [by default is 1: no downsampling] (must be an integer)</p> + </td> + </tr> + <!-- Key 'offset' --> + <tr valign="top"> + <td bgcolor="#f3f4f5"> + <p><tt>OFFSET</tt></p> + </td> + <td bgcolor="#f3f4f5"> + <p>The sample offset for where the downsampling starts counting. By default, this value is + zero so it starts counting from the first sample.</p> + </td> + </tr> + </tbody> + </table> +</p> +<h2><a name="example1">Example 1</h2> +<p> + First we'll create a time-series of random white noise at 10Hz. To do that, + define a <tt>plist</tt> with the key/value pairs shown below, and pass these + to the <tt>ao</tt> constructor. If you're using the workbench, add an <tt>ao</tt> + constructor block to the canvas and select the parameter set "From Time-series Function" and + set the parameters as they are in the <tt>plist</tt> below. +</p> +<div class="fragment"><pre> + <span class="comment">% create an AO of random data with fs = 10 Hz;</span> + pl = plist(<span class="string">'name'</span>, <span class="string">'None'</span>, ... + <span class="string">'tsfcn'</span>, <span class="string">'randn(size(t))'</span>, <span class="keyword">...</span> + <span class="string">'fs'</span>, 10, <span class="keyword">...</span> + <span class="string">'yunits'</span>, <span class="string">'m'</span>, <span class="keyword">...</span> + <span class="string">'nsecs'</span>, 10); + x = ao(pl); <span class="comment">% create AO</span> + </pre> +</div> +<p> + Now we will downsample this data by a factor 5 to 2Hz. We use the method <tt>ao/downsample</tt> and set + the downsample factor in the <tt>plist</tt> as shown below. +</p> +<div class="fragment"><pre> + pl_down = plist(<span class="string">'factor'</span>, 5); <span class="comment">% add the decimation factor</span> + x_down = downsample(x, pl_down); <span class="comment">% downsample the input AO, x</span> + iplot(x, x_down) <span class="comment">% plot original,x, and decimated,x_down, AOs</span> + </pre> +</div> +<img src="images/ltpda_training_1/topic2/down1.png" alt="Downsample" border="3"> +<br> +<br> +<h2><a name="example2">Example 2</h2> +<p> + The <tt>downsample</tt> method takes an 'offset' key which controls where the counting starts. The default is + to output every Nth sample starting with the first. The 'offset' key tells <tt>downsample</tt> to start the counting + from a sample other than the first. The example + below outputs every 4th sample starting from sample 10. +</p> +<div class="fragment"><pre> + pl_downoff = plist(<span class="string">'factor'</span>, 4,<span class="string">'offset'</span>,10); <span class="comment">% add decimation factor and offset parameter</span> + x_downoff = downsample(x, pl_downoff); <span class="comment">% downsample the input AO, x</span> + iplot(x, x_downoff) <span class="comment">% plot original,x, and decimated,x_downoff, AOs</span> + </pre> +</div> +<img src="images/ltpda_training_1/topic2/down2.png" alt="Downsample" border="3"> + + + + </p> + + <br> + <br> + <table class="nav" summary="Navigation aid" border="0" width= + "100%" cellpadding="0" cellspacing="0"> + <tr valign="top"> + <td align="left" width="20"><a href="ltpda_training_topic_2.html"><img src= + "b_prev.gif" border="0" align="bottom" alt= + "Topic 2 - Pre-processing of data"></a> </td> + + <td align="left">Topic 2 - Pre-processing of data</td> + + <td> </td> + + <td align="right">Upsampling a time-series AO</td> + + <td align="right" width="20"><a href= + "ltpda_training_topic_2_2.html"><img src="b_next.gif" border="0" align= + "bottom" alt="Upsampling a time-series AO"></a></td> + </tr> + </table><br> + + <p class="copy">©LTP Team</p> +</body> +</html>