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Joined: 02/11/2002 22:41:59 Posts: 11878 Location: Massachusetts, USA
Posted: Mon Dec 27, 2004 9:22 pm Post subject:
Altitude, uhm... the eternal step child...
For starters, be always aware that altitude information is not very reliable - the VDOP is very high. It improves when you use DGPS, but don't rely on it.
To make matters worse, some SiRF chipsets calculate the altitude offset from the geoid model the wrong way around, and some don't calculate it at all.
Then, verify your Trine's documentation and check that it actually records altitude. I am using a DeLorme BlueLogger (aka Leadtek 9537) which DOES record altitude. _________________ Lutz
Joined: 02/11/2002 22:41:59 Posts: 11878 Location: Massachusetts, USA
Posted: Thu Dec 30, 2004 4:41 pm Post subject:
Can you confirm that you have the firmware shown in the manual? Your data log looks very different from what they show. Why don't you give Emtac support a buzz? _________________ Lutz
Joined: 17/05/2003 02:26:21 Posts: 3747 Location: Bedfordshire, UK
Posted: Sat Jan 01, 2005 8:14 pm Post subject:
I'd be surprised if you were picking up an EGNOS signal in the UK at present; unless things have changed very recently, the only satellite transmitting ETSB (EGNOS test signal) data is PRN131, which is very low to the horizon in the UK.
It's possible you'll pick up PRN131 when airborne - but it's far more likely you're picking up PRN122, which is a WAAS satellite. PRN122 does have some information that will help a bit in Europe, but WAAS doesn't contain wide area differential correction information for Europe.
Meanwhile, the problems that Lutz mentioned only come into play if you are interested in absolute altitude - though they are very real for SiRF based GPSes.
If all you're interested in is your relative altitude during a skydive (or even during a flight, when it should be obvious from the data when you're on the ground), you can easily correct the figures so that when you're at rest you're on the ground.
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