# Thread: [SOLVED] Finding diameter of a cone

1. ## [SOLVED] Finding diameter of a cone

I have a sphere at origin and a known 3d point outside the sphere.
How do I calc the diameter of the cone created by the 3d point
and it's intersection with the sphere (if that makes sense)

Thanks

2. Originally Posted by Blain
I have a sphere at origin and a known 3d point outside the sphere.
How do I calc the diameter of the cone created by the 3d point
and it's intersection with the sphere (if that makes sense)

Thanks
Hello,

I've attached a diagram to show you what I've calculated.

All lines PT form a cone. C is the centre of the sphere. All triangles CTP are right triangles. So the diametre of the cone's base is 2 times the height in the right triangle. The height in a right triangle (and only there) can be calculated by:
$h={{r \cdot TP}\over CP}$

If you know the length of the three lines you only have to plug in the values and caculate the radius of the base.

Greetings

EB

3. Originally Posted by Blain
I have a sphere at origin and a known 3d point outside the sphere.
How do I calc the diameter of the cone created by the 3d point
and it's intersection with the sphere (if that makes sense)

Thanks
Hello,

it's me again:
I've attached a picture which shows sphere and cone from outer space. May be this will help to understand my previous diagram.

Greetings

EB