subSegment method
LineSegment that starts at offset from start and runs for length towards end point
@param offset offset applied at begin of line @param length length of the new segment @return new LineSegment computed
Implementation
LineSegment subSegment(double offset, [double length = -1]) {
Mappoint subSegmentStart = pointAlongLineSegment(offset);
Mappoint subSegmentEnd = length == -1 ? end : pointAlongLineSegment(offset + length);
return LineSegment(subSegmentStart, subSegmentEnd);
}