/// <summary>See <see cref="UnwrapDateline(IGeometry)"/>.</summary>
private static int UnwrapDateline(LineString lineString)
{
var cseq = lineString.CoordinateSequence;
int size = cseq.Count;
if (size <= 1)
{
return(0);
}
int shiftX = 0; //invariant: == shiftXPage*360
int shiftXPage = 0;
int shiftXPageMin = 0 /* <= 0 */, shiftXPageMax = 0; /* >= 0 */
double prevX = cseq.GetX(0);
for (int i = 1; i < size; i++)
{
double thisX_orig = cseq.GetX(i);
Debug.Assert(thisX_orig >= -180 && thisX_orig <= 180);// : "X not in geo bounds";
double thisX = thisX_orig + shiftX;
if (prevX - thisX > 180)
{//cross dateline from left to right
thisX += 360;
shiftX += 360;
shiftXPage += 1;
shiftXPageMax = Math.Max(shiftXPageMax, shiftXPage);
}
else if (thisX - prevX > 180)
{//cross dateline from right to left
thisX -= 360;
shiftX -= 360;
shiftXPage -= 1;
shiftXPageMin = Math.Min(shiftXPageMin, shiftXPage);
}
if (shiftXPage != 0)
{
cseq.SetOrdinate(i, Ordinate.X, thisX);
}
prevX = thisX;
}
if (lineString is LinearRing)
{
Debug.Assert(cseq.GetCoordinate(0).Equals(cseq.GetCoordinate(size - 1)));
Debug.Assert(shiftXPage == 0);//starts and ends at 0
}
Debug.Assert(shiftXPageMax >= 0 && shiftXPageMin <= 0);
//Unfortunately we are shifting again; it'd be nice to be smarter and shift once
ShiftGeomByX(lineString, shiftXPageMin * -360);
int crossings = shiftXPageMax - shiftXPageMin;
if (crossings > 0)
{
lineString.GeometryChanged();
}
return(crossings);
}