/// <summary>
/// Return the result of adding a number to sum (but don't change sum).
/// </summary>
/// <param name="y">the number to be added to the sum.</param>
/// <returns><i>sum</i> + <i>y</i>.</returns>
public double Sum(double y)
{
Accumulator a = this;
a.Add(y);
return(a._s);
}
/// <summary>
/// Clear current instance of <see cref="PolygonArea{T}"/>, allowing a new polygon to be started.
/// </summary>
public void Clear()
{
_num = 0;
_crossings = 0;
_areasum = 0;
_perimetersum = 0;
_lat0 = _lon0 = _lat1 = _lon1 = double.NaN;
}
/**
* Return the results so far.
* <p>
* @param reverse if true then clockwise (instead of counter-clockwise)
* traversal counts as a positive area.
* @param sign if true then return a signed result for the area if
* the polygon is traversed in the "wrong" direction instead of returning
* the area for the rest of the earth.
* @return PolygonResult(<i>num</i>, <i>perimeter</i>, <i>area</i>) where
* <i>num</i> is the number of vertices, <i>perimeter</i> is the perimeter
* of the polygon or the length of the polyline (meters), and <i>area</i>
* is the area of the polygon (meters<sup>2</sup>) or Double.NaN of
* <i>polyline</i> is true in the constructor.
* <p>
* More points can be added to the polygon after this call.
**********************************************************************/
public PolygonResult Compute(bool reverse, bool sign)
{
if (_num < 2)
{
return(new PolygonResult(_num, 0, _polyline ? Double.NaN : 0));
}
if (_polyline)
{
return(new PolygonResult(_num, _perimetersum.Sum(), Double.NaN));
}
GeodesicData g = _earth.Inverse(_lat1, _lon1, _lat0, _lon0, _mask);
Accumulator tempsum = new Accumulator(_areasum);
tempsum.Add(g.S12);
int crossings = _crossings + transit(_lon1, _lon0);
if ((crossings & 1) != 0)
{
tempsum.Add((tempsum.Sum() < 0 ? 1 : -1) * _area0 / 2);
}
// area is with the clockwise sense. If !reverse convert to
// counter-clockwise convention.
if (!reverse)
{
tempsum.Negate();
}
// If sign put area in (-area0/2, area0/2], else put area in [0, area0)
if (sign)
{
if (tempsum.Sum() > _area0 / 2)
{
tempsum.Add(-_area0);
}
else if (tempsum.Sum() <= -_area0 / 2)
{
tempsum.Add(+_area0);
}
}
else
{
if (tempsum.Sum() >= _area0)
{
tempsum.Add(-_area0);
}
else if (tempsum.Sum() < 0)
{
tempsum.Add(+_area0);
}
}
return
(new PolygonResult(_num, _perimetersum.Sum(g.s12), 0 + tempsum.Sum()));
}
/**
* Constructor for PolygonArea.
* <p>
* @param earth the Geodesic object to use for geodesic calculations.
* @param polyline if true that treat the points as defining a polyline
* instead of a polygon.
**********************************************************************/
public PolygonArea(Geodesic earth, bool polyline)
{
_earth = earth;
_area0 = _earth.EllipsoidArea();
_polyline = polyline;
_mask = GeodesicMask.LATITUDE | GeodesicMask.LONGITUDE |
GeodesicMask.DISTANCE |
(_polyline ? GeodesicMask.NONE : GeodesicMask.AREA);
_perimetersum = new Accumulator(0);
if (!_polyline)
{
_areasum = new Accumulator(0);
}
Clear();
}
/// <summary>
/// Add an edge to the polygon or polyline.
/// </summary>
/// <param name="azi">azimuth at current point (degrees).</param>
/// <param name="s">distance from current point to next point (meters).</param>
/// <remarks>
/// This does nothing if no points have been added yet.
/// Use <see cref="CurrentPoint"/> to determine the position of the new vertex.
/// </remarks>
public void AddEdge(double azi, double s)
{
if (_num != 0)
{ // Do nothing if _num is zero
_earth.GenDirect(_lat1, _lon1, azi, false, s, _mask,
out var lat, out var lon, out _, out _, out _, out _, out _, out var S12);
_perimetersum += s;
if (!_polyline)
{
_areasum += S12;
_crossings += TransitDirect(_lon1, lon);
lon = AngNormalize(lon);
}
_lat1 = lat; _lon1 = lon;
++_num;
}
}
/// <summary>
/// Add a point to the polygon or polyline.
/// </summary>
/// <param name="lat">the latitude of the point (degrees).</param>
/// <param name="lon">the longitude of the point (degrees).</param>
/// <remarks>
/// <paramref name="lat"/> should be in the range [−90°, 90°].
/// </remarks>
public void AddPoint(double lat, double lon)
{
lat = LatFix(lat);
lon = AngNormalize(lon);
if (_num == 0)
{
_lat0 = _lat1 = lat;
_lon0 = _lon1 = lon;
}
else
{
_earth.GenInverse(_lat1, _lon1, lat, lon, _mask,
out var s12, out _, out _, out _, out _, out _, out var S12);
_perimetersum += s12;
if (!_polyline)
{
_areasum += S12;
_crossings += Transit(_lon1, lon);
}
_lat1 = lat; _lon1 = lon;
}
++_num;
}
private void AreaReduce(ref Accumulator area, int crossings, bool reverse, bool sign)
{
Remainder(ref area);
if ((crossings & 1) != 0)
{
area += (area < 0 ? 1 : -1) * _area0 / 2;
}
// area is with the clockwise sense. If !reverse convert to
// counter-clockwise convention.
if (!reverse)
{
area *= -1;
}
// If sign put area in (-_area0/2, _area0/2], else put area in [0, _area0)
if (sign)
{
if (area > _area0 / 2)
{
area -= _area0;
}
else if (area <= -_area0 / 2)
{
area += _area0;
}
}
else
{
if (area >= _area0)
{
area -= _area0;
}
else if (area < 0)
{
area += _area0;
}
}
}
private void Remainder(ref Accumulator a) => a.Remainder(_area0);
/// <summary>
/// Construct from another Accumulator.
/// </summary>
/// <param name="a">set <i>sum</i> = <i>a</i>.</param>
public Accumulator(Accumulator a)
{
_s = a._s;
_t = a._t;
}