/// <summary>
/// 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.
/// </summary>
/// <param name="geometry">Input Sql Geometry</param>
/// <returns></returns>
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
var 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
var gnomonicProjection = SqlProjection.Gnomonic(center.Long.Value, center.Lat.Value);
// Project, run geometry MakeValid and unproject
var geometryBuilder = new SqlGeometryBuilder();
geometry.Populate(new VacuousGeometryToGeographySink(geometry.STSrid.Value, new Projector(gnomonicProjection, geometryBuilder)));
var outGeometry = Geometry.MakeValidForGeography(geometryBuilder.ConstructedGeometry);
try
{
return(gnomonicProjection.Unproject(outGeometry));
}
catch (ArgumentException)
{
// Try iteratively to reduce the object to remove very close vertices.
for (var tolerance = 1e-4; tolerance <= 1e6; tolerance *= 2)
{
try
{
return(gnomonicProjection.Unproject(outGeometry.Reduce(tolerance)));
}
catch (ArgumentException)
{
// keep trying
}
}
return(SqlGeography.Null);
}
}
/// <summary>
/// Computes ConvexHull of input geography and returns a polygon (unless all input points are collinear).
/// </summary>
/// <param name="geography">Input Sql Geography</param>
/// <returns></returns>
public static SqlGeography ConvexHullGeography(SqlGeography geography)
{
if (geography.IsNull || geography.STIsEmpty().Value)
{
return(geography);
}
var center = geography.EnvelopeCenter();
var gnomonicProjection = SqlProjection.Gnomonic(center.Long.Value, center.Lat.Value);
var geometry = gnomonicProjection.Project(geography);
return(gnomonicProjection.Unproject(geometry.MakeValid().STConvexHull()));
}