Valid WKTs for SRIDs 4326 and 3857?

[Rumpelstinsk]

I get WKT from https://epsg.io/4326 and https://epsg.io/3857

However that codes throw me an exception when I try to use them:

private void changeSRID(Geometry item, out double lat, out double lng)
        {
            //From coordinate sytem 4326
            var wkt4326 = "GEOGCS[\"WGS 84\",DATUM[\"WGS_1984\",SPHEROID[\"WGS 84\", 6378137, 298.257223563,AUTHORITY[\"EPSG\", \"7030\"]],AUTHORITY[\"EPSG\", \"6326\"]],PRIMEM[\"Greenwich\", 0,AUTHORITY[\"EPSG\", \"8901\"]],UNIT[\"degree\", 0.0174532925199433,AUTHORITY[\"EPSG\", \"9122\"]],AUTHORITY[\"EPSG\", \"4326\"]]";
            GeoAPI.CoordinateSystems.IGeographicCoordinateSystem fromCS =
                ProjNet.Converters.WellKnownText.CoordinateSystemWktReader.Parse(wkt4326, Encoding.UTF8) as GeoAPI.CoordinateSystems.IGeographicCoordinateSystem;

            //To Corordinate system 3857
            var wkt3857 = "PROJCS[\"WGS 84 / Pseudo-Mercator\",GEOGCS[\"WGS 84\",DATUM[\"WGS_1984\",SPHEROID[\"WGS 84\",6378137,298.257223563,AUTHORITY[\"EPSG\",\"7030\"]],AUTHORITY[\"EPSG\",\"6326\"]],PRIMEM[\"Greenwich\",0,AUTHORITY[\"EPSG\",\"8901\"]],UNIT[\"degree\",0.0174532925199433,AUTHORITY[\"EPSG\",\"9122\"]],AUTHORITY[\"EPSG\",\"4326\"]],PROJECTION[\"Mercator_1SP\"],PARAMETER[\"central_meridian\",0],PARAMETER[\"scale_factor\",1],PARAMETER[\"false_easting\",0],PARAMETER[\"false_northing\",0],UNIT[\"metre\",1,AUTHORITY[\"EPSG\",\"9001\"]],AXIS[\"X\",EAST],AXIS[\"Y\",NORTH],EXTENSION[\"PROJ4\",\"+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext  +no_defs\"],AUTHORITY[\"EPSG\",\"3857\"]]";
            GeoAPI.CoordinateSystems.IProjectedCoordinateSystem toCS =
                ProjNet.Converters.WellKnownText.CoordinateSystemWktReader.Parse(wkt3857, Encoding.UTF8) as GeoAPI.CoordinateSystems.IProjectedCoordinateSystem;
                       
            //Transformation
            CoordinateTransformationFactory ctfac = new CoordinateTransformationFactory();
            ICoordinateTransformation trans = ctfac.CreateFromCoordinateSystems(fromCS, toCS);

            double[] fromPoint = new double[] { item.Coordinates[0].X, item.Coordinates[0].Y };
            double[] toPoint = trans.MathTransform.Transform(fromPoint);
            lat = toPoint[0];
            lng = toPoint[1];
        }

I take a look to SRID.csv file of your project, but i couldn't find any ID with 3857.
So, Where can I find the correct WKT for both SRIDs?

[FObermaier]

You should use

// Coordinate systems
var cs4386 = ProjNet.CoordinateSystems.GeographicCoordinateSystem.WGS84;
var cs3857 = ProjNet.CoordinateSystems.ProjectedCoordinateSystem.WebMercator;

// Transformation
var ctfac = new CoordinateTransformationFactory();
var trans = ctfac.CreateFromCoordinateSystems(cs4326, cs3857);

[Rumpelstinsk]

Thanks for the help. That did the trick

[Bernoulli-IT]

Yes this helped. But why don't the WKT definitions, as mentioned by OP, lead to the correct results? That is odd and feels uncomfortable.

[DGuidi]

@Bernoulli-IT I tried to run code posted by @Rumpelstinsk and no exception is thrown

[Bernoulli-IT]

@Bernoulli-IT tried to run code posted by @Rumpelstinsk and no exception is thrown

I think I misplaced my previous comment as I bumped into a similar issue where a conversion resulted in an incorrect y value. My bad.

[airbreather]

Yes this helped. But why don't the WKT definitions, as mentioned by OP, lead to the correct results? That is odd and feels uncomfortable.

This is a valid question. From #37 (comment):

The issue is that the projection "Mercator_1SP" needs additional help to perform the correct conversion.
Out of the box, proj4 wouldn't compute the correct result either, that is why the Extension token is there.

Add [PARAMETER["semi_minor",6378137]] anywhere in the parameter block and you should be all set.
Or use ProjectedCoordinateSystem.WebMercator in the first place.