In the cross section window, any number of cross section sets can be displayed simultaneously, provided they all relate to the same section markers along the primary alignment. Cross section windows open a set of cross sections, but only display one cross section from a set at any instance. A set of cross sections is generated at the time of creation. A set can consist of any number of cross sections. When a cross section set is open in a cross section window it is possible to step through each cross section in the set. To be able to view two or more cross sections from the same set simultaneously, the same cross section set can be opened in more than one cross section window.
When any two cross section sets, or one closed (tunnel) cross section set is open in a cross section window, it is possible to display end areas of cut and fill. If a single closed cross section is displayed, the end area will be the region inside the closed section. Where two cross sections are involved, the cut and fill regions will be defined by the ways that the two sections interact with each other.
To avoid substantial editing, to achieve the desired interactions between the cross sections, a set of rules can be established to interpret the relationships between the sections. These rules are:
- Look for a real intersection between the two surfaces furthest from the centre line;
- Look for a real intersection between the two surfaces furthest from the centre line, but no further than a nominated offset;
- Project the line segment furthest from the centre line out by a nominated slope distance until it intersects the other surface;
- Vertically project the outer extremity point of a cross section so that it intersects the other surface;
- Vertically project a line at a nominated offset so that it intersects both surfaces.
These rules can be applied in any order of priority. Each rule is tested in order. If the rule fails it moves on to the next rule until it finds a rule that passes or it runs out of rules. The rules are applied independently to the left and right of each cross section.