I have two points defined: $A$ and $B$
For both I know $x,y$, longitude, and latitude (gps coordinates). How do I calculate $x,y$ of a third point $C$ when I know its longitude and latitude?
I know this is very basic but I cannot get my head around it at the moment.
Edit: I want a basic math proportion calculation, without taking into consideration Earth's surface and how coordinates is calculated.
Edit: I think I figured it out. (Can't answer my own question yet) for $x$: $\frac{|lon_A-lon_B|}{|lon_C-lon_A|} = \frac{|x_A-x_B|}{|x_C-x_A|}$