Elevation - Best source of data?

So knowing that Elevation is a key factor in accurate MLAT calculations. What’s the best way to get this information?

Google can be +/- 30meters
GPS can be even worse. Best results when you have excellent view of the sky above and horizon, but still can be highly inaccurate…

What other options are there?

Your country’s geological survey map should be pretty accurate. In the UK it would be Ordnance Survey. I’m sure most countries have something similar.

SBAS GPS, like in the US or Europe, should be good to a few metres. Leave the device in one place for a few minutes to allow the clock to stabilise.

In 2020, when Galileo should come online, accuracy should increase, even for civilian use. Aircraft will get a huge benefit when this happens. LPV accuracy virtually around the globe. They also claim that they will have better coverage at higher latitudes.

GPS should be sufficiently accurate for mlat. Note that the FA interface expects height above MSL, not height above ellipsoid (most consumer receivers will show MSL by default).

Errors in height don’t have a huge effect on mlat positions anyway as most aircraft will be close to the horizon so the pseudorange to the aircraft is relatively insensitive to changes in receiver height. So long as you’re within 100m or so it’s not a big deal.

Ohh, I thought after reading another post about the piaware mlat calculations that elevation accuracy was a little more critical than that… I think for my area Google maps data is reasonably accurate to within a meter or 3 given what I get off my phone as well… Just really wanted to know exactly how high above MSL my antenna is and that it was giving accurate results for FA’s mlat. But at least this covers the mlat aspect, thanks Oliver!

A good site is topozone.com/viewmaps.asp? (don’t forget to add the elevation above ground for your location (for example, mine is currently 27’ above ground level, and topozone would show ground level.

heywhatsthat.com supplies this information as well as much more.

It is about 45’ too high for my location (compared to various topo maps I’ve looked at, which are all pretty consistent).

This seems to only be for the US … I am in Brisbane Australia… :confused:

Should be close enough then.