3d digitizing with probe error because of diameter ball tip

hello all,

i am digitizing the side of a motocycle gas tank. i am using a self build 3d probe with a 2,5mm ball tip. the problem is that i get false measurements because of the radius of the ball tip. the highest point of the tank is accurate, the more i get to the angular sides the bigger the error gets. if the wall would be 90° (which is not the case but just for calculating) i would have 1.25mm error, the radius of the ball nose. on 45° sections i have half of that error. since the ball tip cannot touch the tank with its center down part which is zero, there is error. the greater the angle of the side, the greater the error. one can calculate this error with the theorem of phythagoras. the error is in both x and y direction. the error makes the scanned surface flatter than it is.

is anybody aware of software that can solve this problem? or a workarround or trick or something? using a tip with a very small diameter would reduce the error but there would be a problem with softer materials like for example marsclay.

thanks,
michael