Mapping Euler spiral (clothoid) parameters

[rivimey]

Hi... first post here! Sorry if not in the right place.

I am trying to decode the parameters for an xml file format and I would appreciate help in interpreting some parameters. I know the thing specified is a "transition curve" or clothoid curve, as the transition between a straight path and a fixed-radius curve. The parameters I am given are:

*Length (1 floats)
*StartPos (x,y location)
*StartTangent (2 floats)
*CurveSign (1 float - either 1 or -1)
Sharpness (1 float)
Offset (1 float)
OffsetIsZero (bool)
L0 (1 float)
TraversalSign (1 float - either 1 or -1)
L0Offset (4 floats)
L0Tangent (2 floats)

* means these parameters are also seen in a standard curve (together with "Curvature" = 1/radius).
StartTangent is specified as 2 floats which are the args to atan2(x,y)

I believe that StartPos, StartTangent, CurveSign specify the location and direction of the curve at the "straight" end, and Length is the length of the curve (not the chord).

My guess is that the L0 parameters define something about the other, curved end. Most likely L0Tangent is the tangent at that end. I don't know what Sharpness or Offset might relate to.

Can anyone confirm my guesses and/or help with any other suggestions?

The objective us to interpret this data and render the curve as a set of connected line segments in Cartesian coordinates.

Ruth

[I found online a definition of "transition spiral" at http://mysite.du.edu/~jcalvert/railway/transpir.htm which is helpful for background.]

 

[fresh_42]

One cannot answer this without a description of the xml tags. xml is an agreement to exchange data, but the meaning other than encoded in the tags would be guesswork. It looks as if $L0$ is the length of a curve segment or the parameterization in
$$
\begin{bmatrix}x(l)\\y(l)\end{bmatrix} = A\sqrt{\pi} \int_0^l \begin{bmatrix}\cos(\frac{\pi t^2}{2})\\ \sin(\frac{\pi t^2}{2})\end{bmatrix}\,dt
$$