📄 page_289.html
字号:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html> <head> <title>page_289</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_288.html">< previous page</a></td> <td id="ebook_previous" align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_289</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_290.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 289</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">The GPS-only approach has the advantage of not requiring an INS. With two antennas (one baseline), any two angles can be measured. Three antennas (two baselines) are required for full attitude determination. The calculated attitude in the GPS-only approach is insensitive to the length of the baseline vectors, although the accuracy is sensitive to baseline length. The calculated attitude is sensitive to the assumed baseline directions. The GPS-only methods can be used to measure the attitude and azimuth at GPS rates (</font><font face="Symbol" size="3">禄</font><font face="Times New Roman, Times, Serif" size="3"> 10 Hz). If one of the antennas is shaded by the vehicle body or phase lock is lost, vehicle attitude will be unavailable until phase lock can be reestablished.</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 a differential link to a reference station is unavailable, the GPS-only approach can still use double-differencing techniques between the on-board receivers to provide accurate attitude estimation; however, position accuracy will be at the standard GPS position accuracy (tens of meters). With a differential link, high-accuracy position estimation can also be achieved at GPS rates.</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 cost-benefit tradeoff between the GPS-only and the GPS INS approaches to attitude determination is multifaceted. The GPS/INS approach has the advantage of always requiring one fewer GPS antenna than the pure GPS approach. This is due to the use of the INS as the additional source of position information. Therefore one issue is the cost of one additional GPS antenna and either an additional receiver or a more capable receiver relative to the cost of an INS. The INS can have a higher initial cost because of engineering time, but can be cheaper in the long run if many copies will be built. A second issue is the system output rate. Inertial system output rate is limited only by the cost of the computer. Even inexpensive computers can achieve output rates in the kilohertz range. A third issue is the reliability of the system outputs during maneuvers. The GPS INS approach has the advantage of continually providing position, velocity, and attitude or azimuth estimates with estimates of the corresponding error standard deviations even when the GPS antennas are shaded or phase lock is lost. If this information is necessary for vehicle control, then the combined GPS INS approach is strongly motivated. If the GPS INS approach is motivated, the GPS-only attitude solution is still useful for initial alignment.</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 GPS INS approach that was presented assumed the availability of a differential link to attain accurate position and attitude or azimuth estimation. This was assumed to make the one- and the two-antenna examples comparable. Alternatively, double-difference GPS could be used for the second antenna to determine its tangent-plane position relative to the first. This would yield accurate attitude or azimuth estimation with only standard deviation GPS position accuracy in the absence of a differential reference station.</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 major difficulty of all the techniques discussed in this section is that the GPS antenna frame will not coincide with the platform frame under realistic conditions. Although accurate fabrication may ensure that the rotation between the two frames can be accurately modeled by a small-angle transformation matrix, the elements of this matrix must still be determined to achieve the full benefits of the error estimation. For a rigid body, the small angle may be assumed constant. Therefore calibration of the antenna to platform transformation</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_288.html">< previous page</a></td> <td id="ebook_next" align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_289</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_290.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -