Heres is the simple case, that we discussed at the office today.
Given a map in local projection where units are meter. Since we are in denmark and we have some very local projections at our hand I will make an example using two projections here.
First one: http://epsg.io/32632 (UTM 32, a very large local projection)
Second one: http://epsg.io/4097 (DKTM1, a very local projection).
The first Point of interest in both coordinate system:
and the second point of interest in both systems:
Now that we have defined the two points in both system we read out the coordinates for both in both systems and calculate the length between them using Pythagoras.
Distance in DKTM1 (EPSG:4097) is : 3082.372235 Distance in UTM32 (EPSG:32632) is : 3081.193264
So the next question is, what is the accurate actual distance in the real world if we send out a guy on the runway to measure the distance between these two points?
How would i calculate this using mathematics? Reproject to lat,lng and do something there?
I will buy a beer for the one that provides the best example, and you can pick it up at either of the two locations :)