30485pb01 Windscreen 8 x 6 x 3 Curved Top Angled Canopy Pattern, how to finish?

[Magnus Forsberg]

Over at the Part Tracker I wrote this, here:

Ok, I'll try to explain the concept of the conditional line.
(Mainly to myself, but it might help someone else too)
Take two triangles, like this:
3 16 0 0 0 1 0 0 0.5 0 1
3 16 0 0 0 0.5 0.2 -1 1 0 0
Around them are four edgelines.
2 24 0 0 0 0.5 0 1
2 24 0.5 0 1 1 0 0
2 24 1 0 0 0.5 0.2 -1
2 24 0.5 0.2 -1 0 0 0

If there is an angle between these surfaces,
there must also be a conditional/optional line, along their common edge,
like this:
5 4 0 0 0 1 0 0 0.5 0 1 0.5 0.2 -1

not like this:
5 14 1 0 0 0 0 0 0.5 0 1 0.5 0.1 -1
The red line is the only correct one, since the controlpoints
are on the same plane as the farthest points of each of the two tringles.
This conditional line is only visible, if the controlpoints are
below the "horizon" created by the conditional line.
The yellow line has a control point above the end of one of the triangles.
It therefor "disappears" too early.

There is one exception to the rule, cond-lines in primitives always have tangential controlpoints, at their end surfaces.
Cond-lines in a cyli-primitive are made to meet a flat surface next to it.
However, if that surface is placed in an other angle, you must add an extra cond-line.

Edit:
I've attached a file to study. Turn on/off "All conditional lines" and "Show control points" in LDView.