Hi. I'm trying to implement polygon intersection using SAT (Separating Axis Algorithm). There is plenty of nice material on the internet, but there is one particular part of the algorithm that I couldn't understand.

Here are three of the articles I've been reading, just If you wanna take a glance to be sure what I'm talking about:

http://www.phailed.me/2011/02/polygonal-collision-detection/

http://www.codezealot.org/archives/55

http://www.sevenson.com.au/actionscript/sat/

The part I don't understand, is the projection part. You have a normal vector pointing outwards, perpendicular to each edge, and based on that normal, you have to project the shadow of the polygon. But when I read these articles, this shadow seems to be represented by only two values, a min and a max value. This is the part I don't understand.

To clarify. This is an Image of a projection from the third article:

This magenta line is the line I understand is the projection, or the shadow. But how can It be represented by two values? the min an the max? This is a line, and a line as far as I know can only be represented by two points, that is, four values: x1, y1, x2, y2.

So my question is, how is this projection represented by two values and not two points?