Triang track, turnouts and motors for a retro layout

[Il Grifone]

The curve radius and angle also sets the straight rail length. It's the projection of the track centre at the heel of the point to the tangent from the toe. This allows the formation of parallel tracks with the joints in line.

Trix points were 22½º despite the curves being 30º. This required a 7½º quarter curve rail to make up the 30º. IIRC these were supplied with the points which in part explains their high cost.