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Long lines near the poles can degenerate after an unprojection. This occurs with map projections where the pole is a point or a line that is much shorter than the equator. Examples are sinusoidal and Robinson.
If a line is greater than 180 degrees after an unprojection or projection, we force it to become a short line. The line has probably crossed the +/-180 longitude when it shouldn't. For some projections, long lines are valid.
Solution or Workaround
If a line is greater than 180 degrees, force a short line subroutine, add a point in the middle of the line, and reproject it. The results tell you if the line should be long or short.