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SEL685V
Map Matching
NAEL0421S0102
Map matching allows the driver to compare the sensed vehicle
location data with the road map contained in the CD-ROM drive.
Vehicle position is marked on the CD-ROM map. This permits the
driver to accurately determine his/her present position on the high-
way and to make appropriate course decisions.
When GPS data reception is poor during travel, the vehicle posi-
tion is not amended. At this time, manual manipulation of the CD-
ROM map position marker is required.
SEL686V
Map matching permits the driver to make priority judgments about
possible appropriate roads other than the one currently being trav-
eled.
If there is an error in the distance or direction of travel, there will
also be an error in the relative position of other routes. When two
routes are closely parallel to one another, the indicated position for
both routes will be nearly the same priority. This is so that, slight
changes in the steering direction may cause the marker to indicate
both routes alternately.
SEL687V
Newly constructed roads may not appear on the CD-ROM map. In
this case, map matching is not possible. Changes in the course of
a road will also prevent accurate map matching.
When driving on a road not shown on the CD-ROM map, the posi-
tion marker used for map matching may indicate a different route.
Even after returning to a route shown on the map, the position
marker may jump to the position currently detected.
SEL526V
GPS (Global Positioning System)
NAEL0421S0103
GPS is the global positioning system developed and operated by
the US Department of Defense. GPS satellites (NAVSTAR) trans-
mit radio waves and orbit around the earth at an altitude of approxi-
mately 21,000 km (13,000 miles).
GPS receiver calculates the three-dimensional position of the
vehicle (latitude, longitude, and altitude from the sea level) by the
time difference of the radio wave arriving from more than four GPS
satellites (three-dimensional positioning).
When the radio wave is received from only three GPS satellites, the
two-dimensional position (latitude and longitude) is calculated,
using the altitude from the sea level data calculated by using four
GPS satellites (two-dimensional positioning).
Positioning capability is degraded in the following cases.
I In two-dimensional positioning, when the vehicle’s altitude
from the sea level changes, the precision becomes lower.
I The location detection performance can have an error of about
100 m (300 ft) even in three-dimensional positioning with high
precision. Because the precision is influenced by the location
of GPS satellites used for positioning, the location detection
performance may drop depending on the location of GPS sat-
ellites.
I When the radio wave from GPS satellites cannot be received,
GI
MA
EM
LC
EC
FE
CL
MT
AT
TF
PD
AX
SU
BR
ST
RS
BT
HA
SC
IDX
NAVIGATION SYSTEM
System Description (Cont’d)
EL-407
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