Latitude and longitude values from sqlgeometry linestring using C# - latitude-longitude

Question

I recently discovered spatial columns in Microsoft SQL.
I have now successfully stored LINESTRING sqlgeometry with correct EPSG (STRID). Checked by using AutoCAD Map.
The data is now sqlgeometry LINESTRINGs containing groups of X Y coordinates.
Using C# (or an sql statement), how do I get latitude and longitude values of the coordinate points?

Answer 1

What you need is reprojection onto spherical coordinates.
SQL Server does not provides such functionality. You need some plumbing in C# to get your geometries and project coordinates.
If you have your conversion function, using a GeometrySink is fast and would help.
internal class SqlGeometryProjectionSink : IGeometrySink110
{
IGeometrySink110 _sink;
int _outSrid;
Func<double, double, double[]> _coordTransform;
public SqlGeometryProjectionSink(IGeometrySink110 p_Sink, int outSrid, Func<double, double, double[]> coordTransform)
{
_sink = p_Sink;
_outSrid = outSrid;
_coordTransform = coordTransform;
if (_coordTransform == null)
{
_coordTransform = new Func<double, double, double[]>((x, y) => new double[] { x, y });
}
}
void IGeometrySink.AddLine(double x, double y, double? z, double? m)
{
double[] proj = _coordTransform(x, y);
_sink.AddLine(proj[0], proj[1], z, m);
}
void IGeometrySink.BeginFigure(double x, double y, double? z, double? m)
{
double[] proj = _coordTransform(x, y);
_sink.BeginFigure(proj[0], proj[1], z, m);
}
void IGeometrySink.BeginGeometry(OpenGisGeometryType type)
{
_sink.BeginGeometry(type);
}
void IGeometrySink.EndFigure()
{
_sink.EndFigure();
}
void IGeometrySink.EndGeometry()
{
_sink.EndGeometry();
}
void IGeometrySink.SetSrid(int srid)
{
_sink.SetSrid(_outSrid);
}
public static SqlGeometry ReprojectGeometry(SqlGeometry geom, int srid, Func<double, double, double[]> coordTransform)
{
if (geom != null)
{
SqlGeometryBuilder builder = new SqlGeometryBuilder();
SqlGeometryProjectionSink sink = new SqlGeometryProjectionSink(builder, srid, coordTransform);
geom.Populate(sink);
return builder.ConstructedGeometry;
}
return null;
}
void IGeometrySink110.AddCircularArc(double x1, double y1, double? z1, double? m1, double x2, double y2, double? z2, double? m2)
{
throw new NotImplementedException();
}
}
If you don't know the formula you can use for example DotSpatial which provides transformations functions. (see here for an implementation example : https://github.com/xfischer/SqlServerSpatial.Toolkit/blob/4a60154f206af430b27de730afd0340db19f9191/SqlServerSpatial.Toolkit/Viewers/GDI/SqlGeometryReprojection.cs)