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JST Occasional Visitor
Joined: Jun 04, 2005 Posts: 36
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Posted: Wed Jun 22, 2005 7:30 pm Post subject: BT-338 Reporting wrong Elevation |
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Is anyone else seeing their BT-338 reporting the wrong elevation.
OS Maps show my house at an Elevation of 292 ft.
My Etrex Venture averages at around 300 ft, both as reported by the unit itself and by Memory-Map with a fix of 7 satellites. Not bad when I though the the GPS Elevation accuracy was supposed to be about 40 ft.
My BT-338 averagesat an Elevation of 495 ft! - with the same 7 satellites.
Is there anything that can be set on the GPS through SirfDEMO perhaps?
Thanks, Jim |
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JST Occasional Visitor
Joined: Jun 04, 2005 Posts: 36
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Posted: Thu Jun 23, 2005 8:53 am Post subject: |
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A bit more information...
Using SirfDEMO I can now see that the BT-338 is reporting the Elliptical Altitide as 145m (~495ft) and the Altitude above Mean Sea Level (msl) as 90m (~297ft).
I would guess, then, that when they are generating the NMEA frame they are using the Elliptical Altitude. Is the NMEA Protocol unclear about which altitude should be used?
Anyway the upshot seems to be that most NMEA software seems to expect the altitude to be above msi. So is this a bug in the BT-338 firmware?
I would appreciate any thoughts!
Thanks, Jim |
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JST Occasional Visitor
Joined: Jun 04, 2005 Posts: 36
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Posted: Sun Jul 03, 2005 5:50 pm Post subject: |
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Am I the only one seeing this problem?
Its very disconceerting stading on the beach with Memory-Map telling me I am at 180 ft!
Thanks, Jim |
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oddsock Pocket GPS Verifier
Joined: May 01, 2004 Posts: 706 Location: Monmouthshire
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Posted: Sun Jul 03, 2005 9:18 pm Post subject: |
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JST wrote: | Am I the only one seeing this problem?
Its very disconceerting stading on the beach with Memory-Map telling me I am at 180 ft!
Thanks, Jim |
I had a simular reading at sea level useing a Navman BT Gps and BeelineGps software so I contacted their support team who sent me this link to help explain things : http://gpsinformation.net/main/altitude.htm
Dave |
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MrT Frequent Visitor
Joined: Nov 14, 2003 Posts: 2143 Location: Surrounded by A1, M1 & M25
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Posted: Thu Aug 11, 2005 5:59 pm Post subject: |
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My BT-338 shows about 10 feet out at home for altitude whilst at the same time my TomTom GPS is over-reading by some 200 feet. |
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JST Occasional Visitor
Joined: Jun 04, 2005 Posts: 36
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Posted: Thu Sep 01, 2005 2:15 pm Post subject: |
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Just to finish this thread off...
I have now had the Firmware upgrade 3.1 applied by EasyDevices (and a fantastic service it has proved to be!).
I am absolutely certain that before the firmware change the NMEA Protocol $GPGGA record (Field 9 - Antenna Altitude above/below mean-sea-level) was indicating the Elliptical alttitude. It is now definitely using the msl altitude.
Thanks to all those who replied for their thoughts and assistance.
Cheers, Jim |
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