altitude error with navman 3450 / memory map

arsenal_sting · Occasional Visitor Joined: Apr 04, 2005 Posts: 9

i have a Navman 3450 that i use in conjunction with an HP Ipaq 3850. i have just purchased Memory Map that i use for mountain biking. When i use the position indicator on the pocket PC the altitude is significantly in error, it puts my home at almost 100 metres yet it is around 45M. Funny thing is when i plot a route around the street and then import that to the Memory Map on the desktop it shows the elevation time history plot at 40-50 metres, yet if i hover the mouse over the route on the main map it shows the altitude at 100 metres, yet a point next to the route on the map at 40-50 metres. so the data imported from the pocket pc is in error. is the Navman normally this innaccurate at altitude data.

lbendlin · Posted: Mon Apr 04, 2005 11:44 pm Post subject:

Unfortunately yes, and not just the Navman. Most GPS receivers are calculating the altitude correction wrongly or not at all. This leads to effects like the one you observed.

This is such a widely known issue that some topographical software even offers to compensate for that. How sad...
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Lutz

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oddsock · Posted: Tue Apr 05, 2005 1:48 pm Post subject:

I don't know if this has anything to do with it!!
dave

lbendlin · Posted: Tue Apr 05, 2005 2:29 pm Post subject:

Partially yes. But as I stated there are a lot of chipsets and firmware revisions that are providing a wrong value for the altitude correction in the NMEA sequence GGA
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Lutz

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