Calculating using Long/Lat point

[Mike Werner]

Nothing to do with riding, but if I've got a Long/Lat position, how can I calculate all points in a database say within 30 kms from the Long/Lat position ??

 

[ianf]

If you sort of ignore the fact that the distances per degree vary over the face of the earth..

find out in mapsource what 1deg is vertically and horizontally as a distance.

Get an absolute value for the diffence in each coordinate, multiply by the no.s you worked out per degree to get a distance, square both, add them, square-root, and there's your approximate distance. 30km shouldn't have too much of an error in it.

 

[oblertone]

On-call !

You really are bored aren't you !

 

[ianf]

yup. had the aussies on the phone at 7am for advice.... ho-hum.

 

[Greg Masters]

The circumference of the earth is appox 40,000,000 metres.

Each degree of latitude is, therefore, about 111 kms.

Each minute of latitude is about 1,850 metres (approx 1 mile)

Each second of latitude is about 31 metres.

It's a bit more complex for longditude.

At the equator: Each degree of longditude is, therefore, about 111 kms.

But at the poles, each degree of longditude is zero distance.

So the general formula for longditude distance is:

Degrees of latitude from the equator/90 x 111km per degree of longditude.

QED

Greg

 

[Mike Werner]

Hmmmmmmmm. Thanks. Going to be a bit on the difficult side, but I'm going to give it a try.

Never been good at math.