Installation guide

LMU Users Guide

V1.0.6 December 10 2009

- 62 - CalAmp Proprietary & Confidential

9.3.3 GPS Accuracy Threshold

The GPS receiver produces a Horizontal Accuracy Estimate for each position it produces.

The LMU uses this estimate to decide if it should update its position when Pinning. This

estimate threshold is controlled by S-Register 142. If the new position of the GPS Receiver

has an estimate lower than the value in S-142 then the LMU will allow its position to be

updated, otherwise the new position is ignored.

The value of S-142 is in meters. For instance, to set a limit of 10m or better, you would use:

ATS142=10

9.3.4 GPS Fix Quality

The LMU can use its GPS Fix Quality threshold to decide if it should update a pinned

position. If the fix quality received from the GPS receiver is better than the threshold, then

the pinned position is updated, otherwise the position remains the same. The Fix Quality is

defined in bits 0-2 of S-Register 174.

The available settings for S-174 are:

• 0 = Threshold Off

• 1 = Sat Count >= 4 and HDOP <= 3.0

• 2 = Sat Count >= 4 and HDOP <= 2.0

• 3 = Sat Count >= 5 and HDOP <= 2.0

• 4 = Sat Count >= 5 and HDOP <= 1.5

• 5 = Sat Count >= 6 and HDOP <= 1.5

• 6 = Sat Count >= 7 and HDOP <= 1.5

• 7 = Sat Count >= 8 and HDOP <= 1.2

For example, to set a threshold of 5 or more satellites with an HDOP of 1.5 or less you

would use:

AT$APP PARAM 1024,54,7,3

To disable the threshold you would use:

AT$APP PARAM 1024,54,7,0

Please note that S-174 can also be used by PEG in relation to its Moving/Not Moving

Trigger and its GPS Fix Quality Condition.

9.3.5 The effects of Pinning

When the LMU’s position is pinned, the latitude and longitude it reports will be the Pinned

values and not necessarily the latest position produced by the GPS Receiver. This will affect

the contents of an LM Direct, or SMS message in a couple of ways. First off, the Fix Status

bit will indicate that the position is predicted. The second change is that the Time of Fix

value will be the time of the last update used from the GPS Receiver (i.e. the Pinned

location) and may not be the actual time that the message was created. That value will be in

the Update Time field.