Understanding terminal shapes Context Free

In the C++ implementation of context free the primitive shapes are defined as unit shape with center at the origin (where the convention is that y increases in the Northerly direction, ie toward the top of the page/screen). In processing unusually the convention is that y increases in the Southerly direction. This is reflected in the coordinates of the unit shapes of square, circle (irrelevant) and triangle (important).



NB: Click on image to see full size diagram. The top of triangle y = -1 / √3
and the bottom of the triangle is half that ie y = (√3) / 6