WingCell.getLoft() error when using contour coordinates on cells spanning several segments

[joergbrech]

When using the get_loft method with larger models, an unusual behavior occurred: with a small test case (Beam_Composite_Export_Test_32_cell2.xml) with one segment, the get_loft method works for several cells. In a larger test case with several segments (IEA-10.0-198-RWT_CPACS_contour_coordinates.xml), only the cells on the first segment are created correctly. Is that a bug or can only one segment be used with the contour coordinate definition of the cells?

CPACS.zip

Originally posted by @hardt-fa-flb in #815 (comment)

[joergbrech]

This looks like a bug, but I am not 100% sure what is going on yet.

Principally, the contour coordinates support cells that span several segments, but the code behind it is quite complicated, because we have to track the topology of all faces across all segments that are potentially part of the cell, together with their parametric ranges in local u-v-coordinates and in global contour coordinates. In consequence, it is very likely that the code contains bugs.

Thanks for the test file. I will check it out.