Python Line Intersection

Chris Rebert clp2 at
Fri Apr 9 17:44:54 CEST 2010

On Fri, Apr 9, 2010 at 8:04 AM, Peyman Askari <peter_peyman_puk at> wrote:
> Hello
> This is partly Python related, although it might end up being more math related.
> I am using PyGTK (GUI builder for Python) and I need to find the intersection point for two lines. It is easy to do, even if you only have the four points describing line segments ( However, it requires that you solve for two equations. How can I do this in Python, either solve equations, or calculating intersection points some other way?

Just solve the equations ahead of time by using generic ones.

y = mx + b
y = nx + c

We set them equal and solve for x:
mx + b = nx + c
mx - nx = c - b
(m-n)x = c - b
x = (c - b) / (m-n)

So we now have a formula for x. y can then be calculated using the
numerical value of x and one of the original formulas for y.
If your equations are not in slope-intercept form, the same approach
works, just use different, appropriate initial equations.

Alternately, you could use a linear algebra library to solve the
system of equations; NumPy sounds like it has at least part of one.
But this is probably overkill for such a simple problem.

Zero is my hero! Squi FTW.

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