----- Original Message ----- 
From: "Jan-Erik Soderholm" <jan-erik.soderholm@telia.com>
To: <piclist@mit.edu>
Sent: Thursday, December 08, 2005 2:45 PM
Subject: RE: [PIC] DGPS


[DGPS devices]
|
| Yes, but you don't have to own both yourself.
|
| In Sweden that state runs "fixed" GPS'es that resends
| the diff-info and many/some GPS receivers sold in Sweden
| has an built in recevier for this correction info, so they
| are true DGPS devices. There are also option receivers
| for this correction signal that can be attached to a
| non-DGPS receiver, if I'm not wrong.
|
| The correction signal is also sent over the RDS (Radio
| Data System) on the FM band all over Sweden.

As in Austria, too.

|
| Anyway, I've also read that DGPS isn't realy needed
| anymore since the "error" in the GPS signal has been
| removed.

Only half of the truth. There are 3 variants of the GPS signals: a public
one, a commercial useable one and a military signal. The public signal is
not encrypted, the other two signals are (this is only the simplified
description - if you google for GPS you will find the exact story). For the
commercial signal with higher accuracy you have to pay for, the military
signal is - as the name implies - only for military use.

If you want higher accuracy (down to cm-range) with the "simple" public
receiveable signal you have to use DGPS. Even in commercial applications
(f.i. surveying of digged cables) with use of the commercial signal
technicians use DGPS corrections due to higher accuracy.

Regards
Enrico

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