Im trying to use GIMP to measure particle trajectories in a bubble chamber. This requires measuring the radius of curvature of large circular paths with only small sections of the full path. What I've been doing is drawing a line from one endpoint of the partial path to the other. This gives a chord length of the circle. Then, I find the midpoint of the chord and then draw a perpendicular line from this point to the edge of the circle. This gives the saggita length. With the sagitta and chord length I can calculate the radius of the circle. Anyway, to make sure the sagitta line is perpendicular to the chord line deals with very small angles. If I could just type in the angles and points of the lines, it would be much easier and have a lot less error associeated with it. Is there anyway to do this? thankyou much for any replies.