GetLocation is actually mis-documented. It copies the object's scenario location. A scenario location houses the bsp leaf and cluster index that the object is currently located by (this will be fixed in the next release, don't worry).

GetOrigin gets the position of object in the game world. If its a child object, it uses the parent object to calculate its world position.

GetCameraPosition is for unit based objects only and it calculates the view position based on the unit's 'head' if it has one. If not, it will estimate the sight position based on the object's origin.