See discussion at http://scratch.mit.edu/discuss/topic/94194/ *** SOLVED! *** - see http://scratch.mit.edu/projects/50039326/ and the online demo at http://g6auc.me.uk/shear.html Manually fit an ellipse specified by axes and a shear to the same shape specified in a more traditional style by axes and rotation. Can you determine a mathematical mapping of one style of specification to the other? I maintain that it is always possible to map one to the other. Somehow. There are almost certainly multiple mappings. You are unlikely to need to change the positional x,y parameters. If you tweak scale, you can normalise when you're done by multiplying the axes by that value before setting it to 1.
A note on the shear parameter: This is the equation of a line that is added to the image to apply a shear. The intended use is to produce an effect similar to rotating the ellipse. Because this is not quite the same as rotation, the scale parameter is added to make it easier to generate a specific required ellipse. Taken from the original Bresenham implementation by Ruslan Cray https://sites.google.com/site/ruslancray/lab/projects/bresenhamscircleellipsedrawingalgorithm/bresenham-s-circle-ellipse-drawing-algorithm
