Mercurial > hg > ltpda

comparison m-toolbox/html_help/help/ug/ltpda_training_topic_2_4.html @ 0:f0afece42f48

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
Import.
author Daniele Nicolodi <nicolodi@science.unitn.it>
date Wed, 23 Nov 2011 19:22:13 +0100
parents
children
comparison
equal deleted inserted replaced
-1:000000000000 0:f0afece42f48
1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
2 "http://www.w3.org/TR/1999/REC-html401-19991224/loose.dtd">
3
4 <html lang="en">
5 <head>
6 <meta name="generator" content=
7 "HTML Tidy for Mac OS X (vers 1st December 2004), see www.w3.org">
8 <meta http-equiv="Content-Type" content=
9 "text/html; charset=us-ascii">
10
11 <title>Interpolation of a time-series AO (LTPDA Toolbox)</title>
12 <link rel="stylesheet" href="docstyle.css" type="text/css">
13 <meta name="generator" content="DocBook XSL Stylesheets V1.52.2">
14 <meta name="description" content=
15 "Presents an overview of the features, system requirements, and starting the toolbox.">
16 </head>
17
18 <body>
19 <a name="top_of_page" id="top_of_page"></a>
20
21 <p style="font-size:1px;">&nbsp;</p>
22
23 <table class="nav" summary="Navigation aid" border="0" width=
24 "100%" cellpadding="0" cellspacing="0">
25 <tr>
26 <td valign="baseline"><b>LTPDA Toolbox</b></td><td><a href="../helptoc.html">contents</a></td>
27
28 <td valign="baseline" align="right"><a href=
29 "ltpda_training_topic_2_3.html"><img src="b_prev.gif" border="0" align=
30 "bottom" alt="Resampling a time-series AO"></a>&nbsp;&nbsp;&nbsp;<a href=
31 "ltpda_training_topic_2_5.html"><img src="b_next.gif" border="0" align=
32 "bottom" alt="Remove trends from a time-series AO"></a></td>
33 </tr>
34 </table>
35
36 <h1 class="title"><a name="f3-12899" id="f3-12899"></a>Interpolation of a time-series AO</h1>
37 <hr>
38
39 <p>
40 <p>
41 The <tt>ao</tt> class has a method for interpolating data using different forms of interpolation. This method is
42 called <tt>ao/interp</tt>.
43 </p>
44 <p>
45 To configure <tt>ao/interp</tt>, use the following parameters:
46 <table cellspacing="0" class="body" cellpadding="2" border="0" width="80%">
47 <colgroup>
48 <col width="25%"/>
49 <col width="75%"/>
50 </colgroup>
51 <thead>
52 <tr valign="top">
53 <th class="categorylist">Key</th>
54 <th class="categorylist">Description</th>
55 </tr>
56 </thead>
57 <tbody>
58 <!-- Key 'Vertices' -->
59 <tr valign="top">
60 <td bgcolor="#f3f4f5">
61 <p><tt>VERTICES</tt></p>
62 </td>
63 <td bgcolor="#f3f4f5">
64 <p>A new set of vertices (relative to the t0) on which to resample.</p>
65 </td>
66 </tr>
67 <!-- Key 'method' -->
68 <tr valign="top">
69 <td bgcolor="#f3f4f5">
70 <p><tt>METHOD</tt></p>
71 </td>
72 <td bgcolor="#f3f4f5">
73 <p>The method by which to interpolate. Choose from
74 <ul>
75 <li>'nearest' - nearest neighbour</li>
76 <li>'linear' - linear interpolation</li>
77 <li>'spline' - for spline interpolation</li>
78 <li>'cubic' - for cubic interpolation</li>
79 </ul></p>
80 </td>
81 </tr>
82 </tbody>
83 </table>
84 </p>
85 <h2>Example</h2>
86 <p>
87 Here we will interpolate a sinusoid singal on to a new time-grid. The result will be to increase the
88 sample rate by a factor 2.
89 </p>
90 <p>
91 First we create a time-series ao:
92 </p>
93 <div class="fragment"><pre>
94 pl = plist(<span class="string">'Name'</span>, <span class="string">'None'</span>, <span class="string">'tsfcn'</span>,<span class="string">'sin(2*pi*1.733*t)'</span>,<span class="string">'fs'</span>,20,<span class="string">'nsecs'</span>,10,<span class="string">'yunits'</span>,<span class="string">'V'</span>);
95 x = ao(pl);
96 </pre>
97 </div>
98 <p>
99 Then we create the new time-grid we want to resample on to.
100 </p>
101 <div class="fragment"><pre>
102 tt = linspace(0, x.nsecs - 1/x.fs, 2*(x.len));
103 </pre>
104 </div>
105 <p>
106 And finally we can apply our new time-grid to the data using <tt>interp</tt>. We test two of the available interpolation methods:
107 </p>
108 <div class="fragment"><pre>
109 pl_spline = plist(<span class="string">'vertices'</span>,tt);
110 pl_nearest = plist(<span class="string">'vertices'</span>,tt,<span class="string">'method'</span>,<span class="string">'nearest'</span>);
111 x_spline = interp(x,pl_spline);
112 x_nearest = interp(x,pl_nearest);
113 iplot(x, x_spline, x_nearest, plist(<span class="string">'Markers'</span>, {<span class="string">'o'</span>, <span class="string">'+'</span>, <span class="string">'x'</span>}, ...
114 <span class="string">'LineColors'</span>, {<span class="string">'k'</span>, <span class="string">'r'</span>, <span class="string">'g'</span>}, ...
115 <span class="string">'XRanges'</span>, [0 1]));
116 </pre>
117 </div>
118 <img src="images/ltpda_training_1/topic2/interp.png" alt="Interpolate" border="3">
119 <br>
120 <br>
121 <p>
122 To do the same activity on the workbench, we can use a pipeline like:
123 </p>
124 <img src="images/ltpda_training_1/topic2/lwb_interp_1.png" alt="Interpolate" border="3">
125 <p>
126 This teaches some important aspects of the use of the workbench, so it's worth stepping through its construction slowly.
127 </p>
128 <p>
129 To build this pipeline:
130 <ol>
131 <li>Create a new empty canvas</li>
132 <li>Add two MATLAB Expression Blocks:
133 <ol>
134 <li>Right-click on the canvas and choose "Add Block...->MATBlock". A <tt>MATBlock</tt> is a block which can
135 evaluate any valid MATLAB expression and pass that to further blocks via its single output.</li>
136 <li>Select the block, then change its name in the block
137 property table (located at the top left of the "Properties" tab) to 'fs'. Alternatively, the name of the block can be changed by right-clicking on the block and choosing "Set name"</li>
138 <li>Double-click the block to get a pop-up dialog where you can enter the MATLAB expression. In this case
139 just enter the value 20.</li>
140 <li>Select this 'fs' block and hit <tt>ctrl-d</tt> (<tt>cmd-d</tt> on OS X) to duplicate the block.</li>
141 <li>Select the new block and change its name to 'nsecs'</li>
142 <li>Double-click the 'nsecs' block to change its expression. Enter the value 10.</li>
143 </ol>
144 </li>
145 <li>Next we need some additional blocks. Add an <tt>ao</tt> block, two <tt>ao/interp</tt> blocks, an
146 <tt>ao/x</tt> block, and an <tt>ao/iplot</tt> block.
147 </li>
148 <li>Connect up the blocks as shown on the pipeline above.
149 <table cellspacing="0" class="note" summary="Note" cellpadding="5" border="1">
150 <tr width="90%">
151 <td>
152 To add inputs (or outputs) to a block, right-click on the block and choose "Add input".
153 </td>
154 </tr>
155 </table>
156 <table cellspacing="0" class="note" summary="Note" cellpadding="5" border="1">
157 <tr width="90%">
158 <td>
159 Double-click an LTPDA Block to get a dialog box to enter a new name for the block.
160 </td>
161 </tr>
162 </table>
163 <table cellspacing="0" class="note" summary="Note" cellpadding="5" border="1">
164 <tr width="90%">
165 <td>
166 To set the color of the pipes eminating from a particular block, right-click on the block
167 and choose "Set output pipe color" from the context menu. You can also set the color of
168 individual pipes by right-clicking on a pipe and choosing "Set color" from the context menu.
169 </td>
170 </tr>
171 </table>
172 </li>
173 <li>Next we need to set the various properties of each block. Follow these steps:
174 <ol>
175 <li>Set the properties of the AO block to look like:<br>
176 <img src="images/ltpda_training_1/topic2/lwb_interp_ao_props.png" alt="Interpolate" border="3">
177 <table cellspacing="0" class="note" summary="Note" cellpadding="5" border="1">
178 <tr width="90%">
179 <td>
180 The single quotes around the <tt>TSFCN</tt> value are not strictly necessary, but it can
181 avoid problems, for example in the case you have a variable <tt>t</tt> already defined in the MATLAB
182 workspace.
183 </td>
184 </tr>
185 </table>
186 </li>
187 <li>
188 Set the properties of the first interpolate block (a_spline) to look like:<br>
189 <img src="images/ltpda_training_1/topic2/lwb_interp_ao_interp1.png" alt="Interpolate" border="3"> <br>
190 Notice that here we have used the keywords <tt>PORT_1</tt> and <tt>PORT_2</tt> to build the expression. These
191 refer to the ports of that block, and are connected to the MATLAB Expression Blocks which represent the values
192 we are interested in.
193 </li>
194 <li>
195 The block <tt>ao/x</tt> has no properties and simply gets the full x-vector from the output of <tt>a_spline</tt>. This
196 is then passed to the next interpolation block where we use the values as the vertices for the next
197 interpolation step, thus ensuring that the two interpolations are done on the same grid.
198 </li>
199 <li>
200 Set the properties of the second interpolate block (a_near) to look like:<br>
201 <img src="images/ltpda_training_1/topic2/lwb_interp_ao_interp2.png" alt="Interpolate" border="3"> <br>
202 </li>
203 <li>
204 Finally, for the <tt>iplot</tt> block, add three new parameters and give then key names and values
205 like:<br>
206 <img src="images/ltpda_training_1/topic2/lwb_interp_iplot.png" alt="Interpolate" border="3"> <br>
207 </li>
208 </ol>
209 </li>
210 </ol>
211 It should now be possible to run this pipeline and see a plot very similar to the one produced above.
212 </p>
213 </p>
214
215 <br>
216 <br>
217 <table class="nav" summary="Navigation aid" border="0" width=
218 "100%" cellpadding="0" cellspacing="0">
219 <tr valign="top">
220 <td align="left" width="20"><a href="ltpda_training_topic_2_3.html"><img src=
221 "b_prev.gif" border="0" align="bottom" alt=
222 "Resampling a time-series AO"></a>&nbsp;</td>
223
224 <td align="left">Resampling a time-series AO</td>
225
226 <td>&nbsp;</td>
227
228 <td align="right">Remove trends from a time-series AO</td>
229
230 <td align="right" width="20"><a href=
231 "ltpda_training_topic_2_5.html"><img src="b_next.gif" border="0" align=
232 "bottom" alt="Remove trends from a time-series AO"></a></td>
233 </tr>
234 </table><br>
235
236 <p class="copy">&copy;LTP Team</p>
237 </body>
238 </html>