Helper function

This function computes the control point based on weights passed in - the control point is (xwt, ywt) in relative proportion between the two rows in the data frame

compute_control_point(dfs, xwt = 0.5, ywt = 0.5, dir = 0, ...)

Arguments

dfs	dataset
xwt	some weight along x direction
ywt	some weight along y direction
dir	parameter controlling the direction
...	passed on to inside functions