// Convert an input geometry instance to a valid geography instance.
// This function requires that the WKT coordinate values are longitude/latitude values,
// in that order and that a valid geography SRID value is supplied.
//
public static SqlGeography MakeValidGeographyFromGeometry(SqlGeometry geometry)
{
if (geometry.IsNull)
{
return(SqlGeography.Null);
}
if (geometry.STIsEmpty().Value)
{
return(CreateEmptyGeography(geometry.STSrid.Value));
}
// Extract vertices from our input to be able to compute geography EnvelopeCenter
SqlGeographyBuilder pointSetBuilder = new SqlGeographyBuilder();
geometry.Populate(new GeometryToPointGeographySink(pointSetBuilder));
SqlGeography center;
try
{
center = pointSetBuilder.ConstructedGeography.EnvelopeCenter();
}
catch (ArgumentException)
{
// Input is larger than a hemisphere.
return(SqlGeography.Null);
}
// Construct Gnomonic projection centered on input geography
SqlProjection gnomonicProjection = SqlProjection.Gnomonic(center.Long.Value, center.Lat.Value);
// Project, run geometry MakeValid and unproject
SqlGeometryBuilder geometryBuilder = new SqlGeometryBuilder();
geometry.Populate(new VacuousGeometryToGeographySink(geometry.STSrid.Value, new Projector(gnomonicProjection, geometryBuilder)));
SqlGeometry outGeometry = MakeValidForGeography(geometryBuilder.ConstructedGeometry);
try
{
return(gnomonicProjection.Unproject(outGeometry));
}
catch (ArgumentException)
{
// Try iteratively to reduce the object to remove very close vertices.
for (double tollerance = 1e-4; tollerance <= 1e6; tollerance *= 2)
{
try
{
return(gnomonicProjection.Unproject(outGeometry.Reduce(tollerance)));
}
catch (ArgumentException)
{
// keep trying
}
}
return(SqlGeography.Null);
}
}
// Computes ConvexHull of input geography and returns a polygon (unless all input points are colinear).
//
public static SqlGeography ConvexHullGeography(SqlGeography geography)
{
if (geography.IsNull || geography.STIsEmpty().Value)
{
return(geography);
}
SqlGeography center = geography.EnvelopeCenter();
SqlProjection gnomonicProjection = SqlProjection.Gnomonic(center.Long.Value, center.Lat.Value);
SqlGeometry geometry = gnomonicProjection.Project(geography);
return(gnomonicProjection.Unproject(geometry.MakeValid().STConvexHull()));
}
public Projector(SqlProjection projection, IGeometrySink sink)
{
_projection = projection;
_sink = sink;
}
public Unprojector(SqlProjection projection, IGeographySink sink, int newSrid)
{
_projection = projection;
_sink = sink;
_sink.SetSrid(newSrid);
}