Information about an intersection point, e.g. the intersecting component and its geometric relationship to it
NB: The word "intersection" is generally abbreviated to "X" in class names, e.g. XPoint, XList etc. To understand this class, consider the calculation of the intersection between a polygon (with holes) and a line. There could be any number of intersections and, depending on the criteria, might include both actual and projected intersections (where an intersection would occur if the line was extended in either direction). In the first instance, a tool evaluating these intersections might want to stipulate that it is only interested in specific intersections, e.g. only:
- Actual intersections (no projected intersections);
- 'Along' or 'at the origin of' a polygon edge. This is the purpose of the
pos member variable - it describes the relation between the intersecting component (in this case a polygon edge) and the intersection point, e.g. along, origin etc. There will also be equivalent information for the intersecting line, i.e. what is the relation of the intersection point with the line. Once these intersection have been calculated, the tool might need to perform calculations using the intersectig polygon edges (and possibly the intersecting line). This is the purpose of the other member variables, which for this example would be:
vertexIndex: The vertex index at the intersecting edge endpartIndex: The index of the intersecting polygon (0 = the outer polygon boundary, otherwise the index of the hole polygon boundary) Therefore, any intersection calculation will generate 2 Xinfo objects, one for each intersecting component. The list collecting the intersections (see XList) will also include 2 Xinfo objects specifying the criteria for retaining an intersection point.
