// Input argument: the center of the projection
public GnomonicProjection(Dictionary <String, double> parameters)
: base(parameters)
{
_center = SpatialUtil.SphericalRadToCartesian(InputLatitude("latitude1", 90), InputLongitude("longitude1", 360));
// This projection is designed for numerical computations rather than cartography.
// The choice of coordinate basis for the tangent plane - which affects the
// orientation of the projection in the xy plane - is optimized for accuracy rather
// than good looks. The first basis vector is obtained by dropping the smallest coordinate,
// switching the other two, and flipping the sign of one of them. The second one is
// obtained by cross product.
double[] center = { _center.X, _center.Y, _center.Z };
var vector = new double[3];
var k = GetMinEntry(center);
var j = (k + 2) % 3;
var i = (j + 2) % 3;
vector[i] = -center[j];
vector[j] = center[i];
vector[k] = 0;
_xAxis = new Vector3(vector[0], vector[1], vector[2]).Unitize();
_yAxis = _center.CrossProduct(_xAxis);
}
protected internal override void Project(double latitude, double longitude, out double x, out double y)
{
var vector = SpatialUtil.SphericalRadToCartesian(latitude, longitude);
var r = vector * _center;
if (r < _tolerance)
{
throw new ArgumentOutOfRangeException(nameof(latitude), "Input point is too far away from the center of projection.");
}
vector = vector / r;
x = vector * _xAxis;
y = vector * _yAxis;
}
