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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html> <head> <title>page_171</title> <link rel="stylesheet" href="reset.css" type="text/css" media="all"> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> </head> <body> <table summary="top nav" border="0" width="100%"> <tr> <td align="left" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_170.html">< previous page</a></td> <td id="ebook_previous" align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_171</strong></td> <td align="right" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_172.html">next page ></a></td> </tr> <tr> <td id="ebook_page" align="left" colspan="3" style="background: #ffffff; padding: 20px;"> <table border="0" width="100%" cellpadding="0"><tr><td align="center"> <table border="0" cellpadding="2" cellspacing="0" width="100%"><tr><td align="left"></td> <td align="right"></td> </tr></table></td></tr><tr><td align="left"><p></p><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="right"><font face="Times New Roman, Times, Serif" size="2" color="#FF0000">Page 171</font></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">7. Calculate the output residual of the position corrected by the secondary measurement:</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3"><img src="b0bbd7943464b3354cb9e34b50be3ae7.gif" border="0" alt="0171-01.GIF" width="326" height="90" /></font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">8. Calculate the </font><font face="Symbol" size="3">c</font><font face="Times New Roman, Times, Serif" size="3">-squared variable <i>q</i> associated with </font><font face="Symbol" size="3">D</font><font face="Times New Roman, Times, Serif" size="3">y and use it to evaluate the hypothesized integer N</font><font face="Times New Roman, Times, Serif" size="1"><sub><i>p</i></sub></font><font face="Times New Roman, Times, Serif" size="3">. The properly defined </font><font face="Symbol" size="3">c</font><font face="Times New Roman, Times, Serif" size="3">-squared variable <i>q</i> would account for the covariance matrix of </font><font face="Symbol" size="3">D</font><font face="Times New Roman, Times, Serif" size="3">y that is straightforward to calculate P</font><font face="Times New Roman, Times, Serif" size="1"><sub><i>xs</i></sub></font><font face="Times New Roman, Times, Serif" size="3">. However, because of the required number of on-line calculations, the covariance matrix is often dropped in favor of the following simpler calculation:</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3"><img src="b55c534d2b60a9e31fc5d2c4cc6331ee.gif" border="0" alt="0171-02.GIF" width="280" height="35" /></font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">If the hypothesized integer set N</font><font face="Times New Roman, Times, Serif" size="1"><sub><i>p</i></sub></font><font face="Times New Roman, Times, Serif" size="3"> is correct, then <i>q </i>will be small. Depending on the number of satellites available, the noise level, and the satellite geometry, it may take several iteration epochs to identify the correct integer set. In this process, other criteria such as the previously estimated position, the position variance, and the size of N</font><font face="Times New Roman, Times, Serif" size="1"><sub><i>s</i></sub></font><font face="Times New Roman, Times, Serif" size="3"> can also be used to eliminate candidate integer sets.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">Once the correct integers are identified, the algorithm or a simpler variant should be run with <i>q</i> monitored to determine if cycle slips have occurred.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">Note that the algorithm is equally valid for the L1, L2, and wide-lane frequencies. A typical approach is to run the algorithm first to determine the wide-lane integers. Then the increased position accuracy achieved with the wide-lane phase range facilitates the L1 or the L2 integer initialization and search.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">A proper, but more complex, algorithm that properly handles the covariance matrices throughout the integer search process is presented in Ref. 136.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="17"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">5.8<br />Differential GPS</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">The common-mode error sources described previously severely limit the accuracy attainable with GPS. These errors are generally not observable (in the sense described in Chap. 3) with a single receiver unless its position is already known. However, the common-mode errors are the same for all receivers in a local area. Therefore, if the errors could be estimated by one receiver at a known location and broadcast to all other receivers, the GPS accuracy could be substantially improved. This is the basic principle of how DGPS works [70]. Three DGPS techniques are described in the next three subsections. In each case, DGPS involves a GPS receiver/antenna at a location (<i>x</i></font><i><font face="Times New Roman, Times, Serif" size="1"><sub>o</sub></font><font face="Times New Roman, Times, Serif" size="3">, y</font><font face="Times New Roman, Times, Serif" size="1"><sub>o</sub></font><font face="Times New Roman, Times, Serif" size="3">, z</font><font face="Times New Roman, Times, Serif" size="1"><sub>o</sub></font></i><font face="Times New Roman, Times, Serif" size="1"><sub></sub></font><font face="Times New Roman, Times, Serif" size="3">), a receiver/antenna at an unknown, possibly changing, position (<i>x</i></font><i><font face="Times New Roman, Times, Serif" size="1"><sub>r</sub></font><font face="Times New Roman, Times, Serif" size="3">, y</font><font face="Times New Roman, Times, Serif" size="1"><sub>r</sub></font><font face="Times New Roman, Times, Serif" size="3">, z</font><font face="Times New Roman, Times, Serif" size="1"><sub>r</sub></font></i><font face="Times New Roman, Times, Serif" size="1"><sub></sub></font><font face="Times New Roman, Times, Serif" size="3">), and a communication medium from the first receiver to the second receiver. In the discussion of this section, the former receiver will be referred to as the <i>base</i>.</font><font face="Times New Roman, Times, Serif" size="3" color="#FFFF00"></font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table></td></tr></table><p><font size="0"></font></p>聽 </td> </tr> <tr> <td align="left" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_170.html">< previous page</a></td> <td id="ebook_next" align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_171</strong></td> <td align="right" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_172.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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