Map calibration algorithm

[Beo]

hi all,

Any one could show me one map calibration algorithm (used in google map or any map for example).

To calibrate an image, i know that i have to define at least 2 point on that image that will decide some variables for calibration algorithm. And then I should put some points on an calibrated image.

I want to know one algorithm so that when i have one calibrated point P1(Xcal,Ycal) (meter, lon/lat....), I can calculate it to P2(X_image, Y_image) (in pixel) and then draw all points exactly on my image.

Thanks so much for any help :)