Very general question about the implementation of vectors, vertices, edges, rays, lines & line segments

This is just a LARGE generalized question regarding rays (and/or line segments or edges etc) and their place in a software rendered 3d engine that is/not performing raytracing operations. I'm learning the basics and I'm the first to admit that I don't know much about this stuff so please be kind. :)

I wondered why a parameterized line is not used instead of a ray(or are they??). I have looked around at a few cpp files around the internet and seen a couple of resources define a Ray.cpp object, one with a vertex and a vector, another used a point and a vector. I'm pretty sure that you can define an infinate line with only a normal or a vector and then d开发者_JS百科efine intersecting points along that line to create a line segment as a subset of that infinate line. Are there any current engines implementing lines in this way, or is there a better way to go about this?

To add further complication (or simplicity?) Wikipedia says that in vector space, the end points of a line segment are often vectors, notably u -> u + v, which makes alot of sence if defining a line by vectors in space rather than intersecting an already defined, infinate line, but I cannot find any implementation of this either which makes me wonder about the validity of my thoughts when applying this in a 3d engine and even further complication is created when looking at the Flash 3D engine, Papervision, I looked at the Ray class and it takes 6 individual number values as it's parameters and then returns them as 2 different Number3D, (the Papervision equivalent of a Vector), data types?!?

I'd be very interested to see an implementation of something which actually uses the CORRECT way of implementing these low level parts as per their true definitions.

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I'm pretty sure that you can define an infinate line with only a normal or a vector

No, you can't. A vector would define a direction of the line, but all the parallel lines share the same direction, so to pick one, you need to pin it down using a specific point that the line passes through.

Lines are typically defined in Origin + Direction*K form, where K would take any real value, because that form is easy for other math. You could as well use two points on the line.