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.
I would use the path editor and a small script
Just create a "Path" with 3 points on the arc (the farthest apart for accuracy).
The write a small script in Python or Scheme that retrieves the points coordinates from the path and computes the circle center/radius (intersection of any two of the perpendicular bisectors).
This can be done with either Gimp or Inkscape. I can help with the Gimp+Python solution if needed.
I'd try to use Inkscape for this task: import the image and use Inkscape's (path) tools overv it. This will result in SVG files, which could be useful if you need those poths in other media later on, and also lets you measure said paths more easily than GIMP.