How accurate is elevation on google earth, and how is it measured?
I'm trying to find accurate elevation data for our area, but I'm not convinced about how accurate Google earths elevation is. Has anyone else checked it? How is it measured, and how accurately is that info coordinated with the map? Are there any other sites or sources out there that have accurate elevations?
Airport runway elevation is the only place I know of where elevation would be easily findable online and easily comparable to Google Earth.
Just did a quick test with El Paso International Airport. According to FAA data, runway 4 is 3,916.6 feet ASL. Google Earth shows it as 3,921 feet ASL. (Measuring on the number itself, not sure if that's where the FAA measures from.)
Runway 22 is 3,949.2 feet, Google Earth shows it as 3,950. (Oddly enough, runways aren't flat.)
Denver runway 8 is 5,354.3 ASL, Google Earth shows it as 5,358.
DFW runway 35L is 566.5, Google Earth has it at 560.
So - I'm seeing variances of 1-7 feet.
For most people, that's very accurate. Surprised me.
There are several possible sources. Most likely they are using elevation data from the Space Shuttle SRTM mission, which has 90 meter spacing for most of the world. I believe it has 30 meter spacing for the US.
I have read postings that they are also using 10m spacing but thats not confirmed. Maybe only at some special areas.
On a plain surface 90m is fine. But take attention, in high mountain areas the GE elevation is not very accurate. I got a 10m spacing laser-scan modell from my country and I just checked it with the GE elevations.
On a plain area the difference is around 0 -3 meters
On steep hills the difference can be 100 meters (> 300 feet)
If I calculate a 100m spacing elevation modell out of the 10m one, then the difference for the same place could be 60 meters.
Runways not flat
I spend a lot of time in the F-16 cockpit. American runways are reasonably flat, whereas runways in other countries are really a challenge. I am wondering if GE puts the raw elevation data of American runways through some kind of algorithm that flattens them out? If so, that should be applied universally to all airports in the world. It is not necessary to go into flight mode, just put the street view man on a runway in Athens or Tel Aviv, look around, and compare it to Dulles Airport in Washington for example.