Re: Garmin GPS-18 with prn 42 and 50, no DGPS.
- From: Sam Wormley <swormley1@xxxxxxxxx>
- Date: Wed, 24 Oct 2007 19:35:14 GMT
Doug Gray wrote:
Folks,
I am experiencing an odd problem with my GPS-18LVDS from Garmin and was
hoping for some insights.
First, I am located in Australia where at present according to my
GPS-18 we seem to be seeing two WAAS sats in nearly the same location.
These are reported as prn 42 and 50 and both have signal levels of 44-45.
WAAS is a regional augmentation of GPS in North America.
An Essential Element of WAAS and all SBAS implementations -- spatial
correlation [with ground reference stations].
"Differential GPS involves the cooperation of two receivers, one
that's stationary and another that's roving around making position
measurements. The stationary receiver is the key. It ties all the
satellite measurements into a solid local reference." -- Trimble
Navigation Ltd.
The "reference receiver" is a network of ground stations. The WAAS
differential corrections, based on that reference network, are valid
for a WAAS (SBAS) enabled GPS receivers that is within or spatially
close to the associated reference network. One would *not* expect
valid differential corrections from a reference network that exists
on another continent.
-Sam Wormley
http://edu-observatory.org/gps/dgps.html
.
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