BT-338 Reporting wrong Elevation

JST · Occasional Visitor Joined: Jun 04, 2005 Posts: 36

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

JST · Occasional Visitor Joined: Jun 04, 2005 Posts: 36

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

JST · Occasional Visitor Joined: Jun 04, 2005 Posts: 36

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

oddsock · Posted: Sun Jul 03, 2005 9:18 pm Post subject:

MrT · Posted: Thu Aug 11, 2005 5:59 pm Post subject:

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.

JST · Occasional Visitor Joined: Jun 04, 2005 Posts: 36

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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