I want to calculate the intersection of the edge of a marker with a line running from the center to another marker. I want to do this in order to decorate the intersection. I'm using the following code(derived from some code in axes.py) to try and "divine" the size: node_sz=sqrt(size*(ax.figure.dpi.get()/72.0)) This is not right. Clearly, I just don't have an idea what I'm doing (when it comes to calculating the distance along a vector(the along a vector part is easy) of the size of scatter marker). Anyway, who can point me in the right direction would be my hero for atleast 2 or 3 hours. -- Matt