2 horizontal_protrusion + interstem * beamwidth + stemwidth
= beamwidth;
- z2 - z1 = (beamwidth - roundness, beamheight/2);
+% wanske: whole beamheight; or ca 18 degrees
+% z2 - z1 = (beamwidth - roundness, beamheight/2);
+ z2 - z1 = (beamwidth - roundness, beamheight);
z1 + z2 = 2*center;
beamslope = (y2-y1)/(x2-x1);