In East Africa there are various sources for airstrip info, but there’s a wide variation in published lat/long coordinates and altitude data, and I need to update and generate a database – maybe to share with other pilots (non-commercial).
What’s the best way of harvesting the info? Stand in the middle of an airstrip, clutching an iDevice (other kit available) and screenshooting Google Maps, or a Compass app?
This is before visiting the airfield with an aircraft and GPS.
I personally would start with Google Earth
Google Maps / Google Earth should be easily accurate enough to get the coordinates.
Some countries have demanded that Google reduces the resolution of certain areas, but I am not aware that the coordinates of some places have been shifted.
It won’t be full GPS accuracy; I am sure this is intentional otherwise you could send a missile to somebody’s house. But it will be good enough for flying to the place.
I used these methods to calibrate maps, including city maps, for Oziexplorer, in the bad old days.
The altitude from a phone or a tablet is not likely to be accurate though.
Google Earth terrain height is generally accurate enough to use.
When I was building the GPS_ILS database, I found GoogleEarth almost uncannily accurate against published data.
But you do need to take the Geoid into account, and that may not be as well mapped in Africa? (I have no idea, but it seems likely.)
Peter wrote:
I am sure this is intentional otherwise you could send a missile to somebody’s house
I think if you are able to get you hands on GPS guided missile you are are probably able to get the coordinates of the house you want destroyed from something other than google maps (also, most of the missiles will have visual terminal guidance) – I can’t see why on earth (pun intented) google maps would introduce errors to prevent that sort of situation.
What’s working for me at the moment, and I’m sure there’s a neater way, is to locate the approx. position of an airfield via Google Earth viewed ‘through’ Sky Demon, pin down the exact strip, use the SD ruler gadget (distance along track and track) to find the exact centre of the strip, and create an airfield to be shared with my other iDevices, or just note the lat/long coordinates. This can then be exported to Garmin kit (GTN in my case). Checking the 3D view, although out-of-date, for trees, pylons etc. looks possible.
Any recommendation for an intro to Geoid data would be appreciated.
