# Check if 3D Point is below a line

Is it possible to know if a point in below a direction vector or a line? I'm not good at maths and I'm having a really hard time figuring this out, I seen some answers to doing this in a 2D but can't find anything for 3D.

I have a capsule that is laid horizontally and I want to know if a point is below or above a line which goes through the bottom of the capsule to the top of the capsule. I attached an image that might explain it a bit better.

Drawn in 2d

I have a Position Vector for the point, direction vector of the capsule, and the position vector of the capsule. and I can find the bottom and the top of the capsule if needed.

• What do you mean by "below" – Don Thousand Mar 23 at 3:42
• Sorry English isn't my first Language, i don't really know how to explain it anymore. Its like the image i drew but instead of it being 2d space, I want to check it in 3d space. I saw someone refer to it as a Plane (like a sheet of paper) in 3D space and i want to know if random point is above or below that plane (z axis) – ChaosDuck Mar 23 at 3:54
• Below means something specific in 2D space which doesn't have a direct analogue in 3D space. As such, with imprecise definitions, it's not possible to make progress. – Don Thousand Mar 23 at 3:55
• Edited the comment above, i will make another picture when i get on my pc. Lets say that have 2 points right A(100, 2838, 10) with Z being the up direction and then I have B(9999, 3985, -100) now if i ignore the x and y values I know that the Z or the height of the A is greater than B. But now instead of the point A, I have 2 points in 3d space, is it possible to check if point B is above or below this like (taking the z value as the up and down). Also i don't know if people call it a plane instead of a line. – ChaosDuck Mar 23 at 4:06