GPS
The position calculation procedure is indicated in the following three steps:
1. GPS satellites continuously transmit their own precise orbital data and the GPS receiver comp
utes their locations by receiving this data.
2. In this receiving process, the GPS receiver measures very accurate distances to the satellites,
using the "Spread Spectrum Modulation" method. Excellence in GPS's position-fixing accuracy
is mainly due to this technology.
3. When the satellite locations and their distances are known, the GPS receiver fixes its own pos
ition by triangulation:
[The GPS position calculation]
As illustrated in the previous figure, the position is calculated as the meeting point of three
spheres which are drawn around the three satellites with diameters d1, d2 and d3.
Position Fixing Accuracy: HDOP
The GPS fix accuracy is due to the locations of 3 satellites in the sky. High accuracy is obtainab
le when the satellites are widely scattered in the sky; on the
contrary, accuracy is reduced when the satellites have gathered in a narrow space. In the followi
ng figure, in both cases it is possible to obtain the GPS fix, but in the left case the accuracy will
be higher than the right:
[HDOP]
The index for position-fixing accuracy is called HDOP (
"Horizontal Dilution Of Precision"
). The s
maller the HDop value, the more accurately the position can be fixed.
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Summary of Contents for AQUA HGP-660
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