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List:       gpsd-dev
Subject:    [gpsd-dev] [PATCH 3/4] Correct how DGPS works, and types (SBAS, GBAS)
From:       Sanjeev Gupta <ghane0 () gmail ! com>
Date:       2015-04-14 14:11:21
Message-ID: 1429020682-25303-3-git-send-email-ghane0 () gmail ! com
[Download RAW message or body]

---
 www/gps-hacking.html | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/www/gps-hacking.html b/www/gps-hacking.html
index 121952c..61dffaa 100644
--- a/www/gps-hacking.html
+++ b/www/gps-hacking.html
@@ -144,12 +144,13 @@ the signals.  The U.S. military knew the pattern, but nobody else did
 natural.  One is a variable amount of signal lag produced as the GPS
 signals pass through the ionosphere, which partly refracts radio
 waves.  This can be largely compensated for by a technique called
-"Differential GPS" or DGPS, in which your receiver takes timings both
-from satellites and ground stations.  The ground stations are in a
-known fixed positions, so they can compute the exact distance to
-satellites from an ephemeris. Thus, they can measure the for the
-ionospheric lag and tell nearby GPSes how to correct ranges for it.
-WAAS and EGNOS are similar systems.  See <a href="#ggps">DGPS, WAAS,
+"Differential GPS" or DGPS.  Ground stations are established in
+known fixed positions, and compare their calculated GPS locations
+with their known values.  Thus, they can measure for the
+ionospheric lag and tell nearby GPSes the corrections required.
+This information may be broadcast via radio (Ground Based Augmentation
+Systems), or via satellites (Space Based Augmentation Systems).
+Examples of SBAS are WAAS and EGNOS.  See <a href="#ggps">DGPS, WAAS,
 and EGNOS</a> for details on how this works.</p>
 
 <p>In practice, the most important limit on accuracy is the actual
-- 
2.1.4


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