Does point C fall on the left side of the AB line?

Source: R/start_left.R

Returns TRUE if the point C fall on the left side of the AB line. Orientation of the AB line determines the left and right side (i.e, starting at point A looking toward point B). Used to answer the question: Is point C on the left of the AB line?

start_left(a_x, a_y, b_x, b_y, c_x, c_y)

Arguments

a_x

numeric, Point A x coordinate

a_y

numeric, Point A y coordinate

b_x

numeric, Point B x coordinate

b_y

numeric, Point B y coordinate

c_x

numeric, Point C x coordinate

c_y

numeric, Point C y coordinate

Value

logical

Details

Uses the cross product method. Taken from: [SO](https://stackoverflow.com/questions/1560492/how-to-tell-whether-a-point-is-to-the-right-or-left-side-of-a-line)