Calculation of s-t coordinates using t-axis definition

[weissdavid]

Describe the feature

The current definition of s-t coordinates relative to a reference line has two issues on the corners (multiple points with same coordinates on the outside, discontinuity on the inside). I would like to suggest a modification of the calculation that solves this problems and gives s-t coordinates that are closer to OpenDRIVE.

Describe the solution you would like

For each ReferenceLinePoint a new field defining the t-axis (i.e. all points with the same s coordinate) is introduced. Points outside the reference line or then projected onto the reference line not orthogonally (as in the current definition) but by drawing the straight line of the point to the intersection of the t-axes of the appropriate section (see sketch). s and t coordinate are then calculated as in the current definition (s is the s coordinate of the projection point, t is the euclidean distance to the projection point).

Describe the backwards compatibility

If the t-axis is not defined, one could instead use the angle bisector for the same calculation.

Additional context

For a possible implementation of this calculation see Proposal calculation s t.docx

[ReinhardBiegelIntech]

Looks like this is already addressed in v3.6.0 via #651?