ArcObjects GCS to PCS

[ShaningYu]

I have a point FC in a mxd file in WGS_1984_Web_Mercator_Auxiliary_Sphere, and displays in Decimal Degrees (Long/Lat).  I published it as a mapservice, and retrieved the features in my SOE project.  However, the features' Extent are not in Long/Lat.  Then, I used the piece of code below to convert the X/Y from GCS to PCS (in meters) but it does not work. What's wrong in my code?  Thanks if you can help.

	public IPoint CoordinateConvert(IPoint point, string[] srID)  {
	ISpatialReferenceFactory srFactory = new SpatialReferenceEnvironmentClass();
	ISpatialReference srTo;
	IProjectedCoordinateSystem pcs = srFactory.CreateProjectedCoordinateSystem(Convert.ToInt32(srID[0]));
	srTo = pcs;
	IGeometry geometry;
	geometry = point;
	geometry.SpatialReference = point.SpatialReference;
	geometry.Project(srTo);
	point = geometry as IPoint;
	double x, y;
	point.QueryCoords(out x, out y);
	System.Diagnostics.Debug.Print("X: " + x.ToString());
	System.Diagnostics.Debug.Print("Y: " + y.ToString());
	return point;
	}

[ShaningYu]

referring to .net - How to convert lat long to meters using Mercator projection in C# - Geographic Information Sy... , I coded like that and solve this problem.  Thanks for your reviewing.

	public IPoint Convert_GCS2PCS(IPoint pt) {
	double lon = projDeg2Rad(pt.X);
	double lat = projDeg2Rad(pt.Y);

	double lon0 = 0;
	double sm_a = 6378137.0 ;
	double sm_b = 6356752.314;

	double x = x = sm_a*(lon-lon0);
	double y = sm_a*System.Math.Log((System.Math.Sin(lat)+1)/System.Math.Cos(lat));

	IPoint pt2 = new Point();
	pt2.X = x;
	pt2.Y = y;
	return pt2;
	}

	public double projDeg2Rad(double deg) {
	return (deg / 180.0 * System.Math.PI);
	}

[MelitaKennedy · Accepted solution]

Yes, the second code sample you posted does convert lat/lon to "Web Mercator" which is also known by several well-known IDs including EPSG:3857, OpenLayers:900913, and Esri:102100. The sm_b line isn't needed because this projected coordinate system uses a sphere so only the semimajor axis also known as "a" is used. What srID were you passing in the first code sample? It should have been 3857 or 102100.

Melita

[ShaningYu]

You are right.  I use 102100.  I used another piece of code for general conversion about 1.5 yrs. for the same purpose.  After I dig it out, I will update the thread.  Thanks.