Perpendicular on a line segment from a given point

Question

I want to calculate a point on a given line that is perpendicular from a given point.

I have a line segment AB and have a point C outside line segment. I want to ca

Answer 1

Here is a python implementation based on Corey Ogburn's answer from this thread.
It projects the point q onto the line segment defined by p1 and p2 resulting in the point r.
It will return null if r falls outside of line segment:

def is_point_on_line(p1, p2, q):

    if (p1[0] == p2[0]) and (p1[1] == p2[1]):
        p1[0] -= 0.00001

    U = ((q[0] - p1[0]) * (p2[0] - p1[0])) + ((q[1] - p1[1]) * (p2[1] - p1[1]))
    Udenom = math.pow(p2[0] - p1[0], 2) + math.pow(p2[1] - p1[1], 2)
    U /= Udenom

    r = [0, 0]
    r[0] = p1[0] + (U * (p2[0] - p1[0]))
    r[1] = p1[1] + (U * (p2[1] - p1[1]))

    minx = min(p1[0], p2[0])
    maxx = max(p1[0], p2[0])
    miny = min(p1[1], p2[1])
    maxy = max(p1[1], p2[1])

    is_valid = (minx <= r[0] <= maxx) and (miny <= r[1] <= maxy)

    if is_valid:
        return r
    else:
        return None