# Geometry :

Subject: [ggl] Re: Finding intersection points of a ray and polygon?
From: Elvis Stansvik (elvstone)
Date: 2010-02-22 18:05:06

2010/2/22 Elvis Stansvik <elvstone_at_[hidden]>:
> Hello GGLers,
>
> For a very small high-school project I'm making a simple Qt
> application that should let my teacher illustrate the Law of
> refraction [1] to his students.
>
> The idea is to let the user of the application place a set of simple
> bodies (polygons) with optical properties into a scene and then let a
> ray of light pass through them. With ray I mean a line which is finite
> in one direction but infinite in the other.
>
> This requires me to find the ray's first intersection point with a
> polygon. As I don't have quite a lot of math under my belt, and the
> project is very small and done under time constraints I started
> looking for a computational geometry library and found Boost.Geometry
> which seems to fit the bill.
>
> Now my question is; can Boost.Geometry help me find the first
> intersection point of a ray and a polygon, and after that also give me
> access to the polygon edge that was hit? (I will need the angle of the
> edge to do the refraction calculation).
>
> I'm very open to to ways in which I can simplify my project, as I only
> have a few weeks. Just using simple convex polygons for the optical
> bodies would be OK, and also using a line segment of finite length
>
> Any pointers and tips to examples besides the one on the User Wiki and
> reference documentation are much appriciated. My C++ proficiency is
> OKish and my template programming knowledge definitely rusty ;)
>
> Finally, congrats to getting GGL into Boost proper.
>
> Best regards,
> Elvis Stansvik
>

>

I realized after sending my mail that I have an additional question:

For my application I would need to know if (at the intersection point)
the ray is passing into or out of the polygon. Can Boost.Geometry give
me this information?

Regards,
Elvis

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