[aprssig] Re GPS off track

[Phillip]

Hi Stephen,
                        The GPSmart is manually set to WGS84 and the
Globalsat is default WGS84
Both are SIRF powered both give the same amount of error I am wondering if
there is an error in the chipset .
 
http://www.fortuna.com.tw/gpsmart.htm                 GPSmart

http://www.globalsat.com.tw/eng/product_detail_00000044.htm             
Globalsat BU-353

73 Phillip
ZL2TZE

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Message: 14
Date: Wed, 02 Apr 2008 02:05:47 -0700
From: "Stephen H. Smith" <wa8lmf2 at aol.com>
Subject: Re: [aprssig] GPS off track
To: TAPR APRS Mailing List <aprssig at lists.tapr.org>
Message-ID: <47F34C6B.9060206 at aol.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
 
Phillip wrote:
> Hi,
>      Have am using a Toshiba Laptop Satellite 2140CDS, AGW engine,,
> UI-View
> 32, and a DRSI TNC2 as my mobile tracker
>
> I have 2 New GPS units a GPSmart 12 channel  and new today a Globalsat
> BU-353 SIRF powerd both of them
>
> Both these GPs give me an error of 55 mtrs East and 30 North in
> Google  when
> checking with www.aprs.if   and www.findu.com
>
> I did a track tonight   (02/04/08 NZT)   zl2tze-15 with the new BU-353 it
> has me not packed at my correct address.
>
> On Saturday  ( 29/03/08)  I travelled to Nelson using the GPSmart GPS
> this
> also has the same error.
>
> Is this a GPS , UI-View , an error in the Google maps  or is it that
> these
> cheaper GPS units are not the great ???
>
> My correct address is zl2tze-4 on the Maps Google
> Any help on this will be appreciated
> 73 Phillip
> ZL2TZE
>
>
>
 
What datum are the GPS units set for?   If they are not set to WGS84
(WORLD Geodetic System 1984) mode, you will see hundreds of feet error.
 
This is a constant issue in the U.K. where many paper and electronic
maps use the British Ordinance Survey datum rather than the WGS84 datum
that is native and default on most GPS devices.    Google Maps (used by
both findu and aprs.fi) are aligned with the world-wide GPS-inspired
WGS84 datum.    Many British APRS users set their GPS units to use the
UK ordinance datum to make posits line up on their own maps;  only to
see major errors when they view themselves on Findu or aprs.fi.
I would guess that Australia and New Zealand may also suffer from this
problem of a "local" datum in use rather than the world-wide WGS84.
(The Brits established numerous local datums during the centuries of the
British Empire in places all over the world.)
 
 
 
 
--
 
Stephen H. Smith    wa8lmf (at) aol.com
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