calculating edge vectors

You're probably going to have to multiply delta-X and delta-Y by the sin and cos of the angle of deflection. Not sure which delta will be multiplied by sine and which by cosine, but that shouldn't be too hard to suss out.

You will need some knowledge about Hermite/Bezier splines. Perhaps you download my "track builder" mod* and have a look at scripts/wktb_geoutil.lua. The functions that you need for constructing, rotating and placing curves are

geo.createFullCurve**

geo.createPositiveCurve**

geo.rotTranslEdge

geo.rot

I always construct a curve from the zero point and then shift and turn it with geo.rotTranslEdge to the place I want to have it. Mostly this is the end of the preceding edge.

The variables used are:

r: radius

radiant: angle in rad

curved: -1 left, 1 right

zEnd: end height

mConn: end slope of preceding edge

mEnd: slope of the end of current edge

pConn: end point of preceding edge

tConn: end tangent point of preceding edge

Sometimes I use different names for the points:

p0 / pStart: start point

p1 / pEnd: end point

t0 / tStart: left tangent point

t1 / tEnd: right tangent point

A special feature of my curves is to build them in at least two parts. This was necessary beacause TPF crashed when building an intersection with a segment only from one edge. I have not yet tested if this issue still exists.

The basics for handling Hermite and Bezier splines you can find here:

Kurven konstruieren

Punkte, Vektoren, Koordinaten in Lua programmieren

I intended to continue this to make a tutorial from it, but I didn't yet finde the time. It is not a simple stuff, so if you have questions perhaps we can start a conversation - or for simpler things I'll try to post the answer here.

*) Latest version, former versions use a more complicated algorithm.

**) You can leave out the last argument in the lines 74 and 93, it was originally thought for another purpose, but p0 will always be {0,0,0}, so this is not necessary.