Returns the projection function of grain boundary segments based on Panozzo R (1984) "Two-dimensional strain from the orientation of lines in a plane." J Struct Geol 6:215–221
Surfor makes only sense for sufficiently smooth grain boundaries.
|lp||cummulative projection length|
|omega||list of angles used for the projection|
|stepwidth||width of interval for angles 0:pi (default: 1 degree)|