Where am I? Sensors and Methods for Mobile Robot Positioning
Where am I? Sensors and Methods for Mobile Robot Positioning
Where am I? Sensors and Methods for Mobile Robot Positioning
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Chapter 3: Active Beacons 87<br />
100.0<br />
90.0<br />
80.0<br />
70.0<br />
60.0<br />
50.0<br />
40.0<br />
30.0<br />
20.0<br />
10.0<br />
0.0<br />
97.7 97.3 96.2<br />
93.3<br />
82.2<br />
17.8<br />
6.7<br />
0.0 0.0<br />
2.4 2.7<br />
0.0 1.6 2.2<br />
0.0<br />
Magellan Magnavox Engine Rockwell NavCore Magnavox 6400 Trimble Placer<br />
% No Navigation % 2-D Navigation % 3-D Navigation<br />
Figure 3.13: Navigation mode data <strong>for</strong> the static test. (Adapted from [Byrne, 1993].)<br />
Table 3.12 relates all of the different DOP criteria to the PDOP. Based on the in<strong>for</strong>mation in<br />
Table 3.12, several comments can be made about the relative stringency of the various DOP<br />
criterions. First, the Magnavox GPS Engine VDOP criterion is much less stringent than the Magellan<br />
VDOP criterion (these two can be compared directly). The Magellan unit also incorporates<br />
hysteresis, which makes the criterion even more stringent. Comparing the Rockwell to the Trimble<br />
Placer, the Rockwell criterion is much less stringent. A TDOP of 10.2 would be required to make<br />
the two criteria equivalent. The Rockwell <strong>and</strong> Magnavox GPS Engine have the least stringent DOP<br />
requirements.<br />
Taking into account the DOP criterions of the different receivers, the significant <strong>am</strong>ount of twodimensional<br />
navigation exhibited by the Magellan receiver might be attributed to a more stringent<br />
DOP criterion. However, this did not improve the horizontal (latitude-longitude) position error. The<br />
Magnavox GPS Engine still exhibited the most accurate static position per<strong>for</strong>mance. The s<strong>am</strong>e can<br />
Table 3.12: Summary of DOP - navigation mode switching criteria. (Courtesy of [Byrne, 1993].)<br />
Receiver 2-D/3-D DOP criterion PDOP equivalent<br />
Magellan<br />
Magnavox GPS<br />
Engine<br />
Rockwell NavCore V<br />
Magnavox 6400<br />
If 4 satellites visible <strong>and</strong> VDOP >7, will<br />
switch to 2-D navigation.<br />
Enters 3-D navigation when VDOP10,<br />
switches to 2-D navigation.<br />
If HDOP>10, suspends 2-D navigation<br />
If 4 satellites visible <strong>and</strong> GDOP>13,<br />
switches to 2-D navigation.<br />
Data Not Available in MX 5400 manual<br />
provided<br />
2 2 ½<br />
PDOP > (HDOP + 7 )<br />
2 2 ½<br />
PDOP < (HDOP + 5 )<br />
2 2 ½<br />
PDOP > (HDOP + 10 )<br />
2 2 ½<br />
PDOP > (13 - TDOP )<br />
Trimble Placer If 4 satellites visible <strong>and</strong> PDOP>8, switches to 2-D<br />
navigation. If PDOP>12, receiver stops navigating.<br />
PDOP > 8
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