Base Camp altitude conflicting with Google Earth

BaseCamp gets its altitude from the map you have selected. In my view it's more likely to be wrong than GE, but to be sure you could check by using a different map in BaseCamp.

A 500 ft error seems awfully large. Is the altitude value off of downloaded data or off the map? Which map and/or device? Can you provide example coordinates?

Thanks for the quick replies gentlemen! This is for an epix watch, and I'm doing all my work on Base Camp using the worldwide basic map that came pre-loaded. The coordinates in question are; [h=1]12?47'48.2"N 102?36'56.3"E[/h] Google Earth shows altitudes of 1300 - 1320 feet for that particular area, whereas Base Camp using the worldwide dem map shows 1800 - 1820 feet. My other waypoints in the vicinity, are close enough (50 meters difference here and there) but the one in question is very important, I need it to be as true as possible. I'm not sure where else to find true altitude? Any and all help is MUCH appreciated!!

Bill

The world wide dem that comes on a device will likely be less accurate than Google Earth because available memory on the device will limit the density of the DEM. But at that location, it is hard to say how good Google Earth will be.

I asked about your device in case your elevation from a recorded point. If your device as a barometric sensor, then elevation the recorded elevation will based on the sensor and not the gps solution. With sensor equipped devices it is vital to calibrate the barometer before collecting data if elevation is of interest.

With sensor equipped devices it is vital to calibrate the barometer before collecting data if elevation is of interest.

Good point, I'm not in Cambodia but I will be in a few months.. I will confirm the data when I get to those points in person, using the actual gps elevation as well as calibrating the altimeter with the local sea level pressure. I will also cross-reference with 2 or 3 additional gps units and barometric altimeters. I should be able to dial it in pretty precise when I'm there. The reason I'm trying to nail it down now, is because I'm creating my own customized maps to print out and laminate in the event that my electronics fail. I'm packing a Cammenga model 27 and some pocket Silva compasses to use with my backup maps. I'll be trekking 6 - 12 miles into virgin tropical jungle without a guide, so I'm going extra heavy on the redundancy ;)

Always a good idea to carry compass and physical map.

The set-point in device sensors can be off, so setting the altimeter by know elevation is best. But you can check this ahead of time by noting setting the device by known elevation then noting the barometric reading and comparing it to reported values. Note the difference pressure and apply it when setting the altimeter with a known pressure.

Also, Garmin devices have a feature called continuous calibration where the barometric pressure is periodically corrected based on gps elevation. I recommend that you play with this feature ahead of time. You should test it on a day where pressure will be reasonably stable and on a day when a front passes through and pressure variation is expected. I don?t have enough experience with this feature to advise you to turn it on or off.

Enjoy your trip.

Solid advice my friend, thanks for the great tip - comparing the pressure reading with local weather station or airport data for a known altitude, then using the pressure difference (if any) as a future reference to gauge the real altitude of anywhere else! LOVE IT !!

Does anyone know where I can purchase/download a good Cambodia or even a complete SouthEast Asia Topo map for Garmin devices?? I spent every bit of an hour searching online to no avail. I did find some 'home brew' GPX type maps from unfamiliar sources that I don't really want to gamble with unless that's my only option. I was surprised that I couldn't find anything readily available from Garmin... any ideas or recommendations??

Thank you again for your time and thoughtful answers,
Bill

Here is probably your best bet http://garmin.openstreetmap.nl/

FANTASTIC !! Already downloaded all the Cambodian maps and installed in Base Camp and on device! Great website ! Thank you !! If you gentlemen ever want to visit Cambodia, all you need is a plane ticket, the rest of your holiday is on me!