Converting coordinates from EPSG 3857 to 4326 DotSpatial

In the end I find a math formula to convert the coordinates.

I implemented it in a stored procedure because I have a list of point and this stored procedure calculates the distance.

DECLARE @e FLOAT=2.7182818284
DECLARE @X DECIMAL(18,2) =20037508.34

SET @StartLat3857 =(SELECT TOP 1 Latitude FROM Coordinates WHERE IdCoord=@IdCoord ORDER By IdTDFPath ASC)
SET @StartLng3857=(SELECT TOP 1 Longitude FROM Coordinates WHERE IdCoord=@IdCoord ORDER By IdTDFPath ASC)

--converting the logitute from epsg 3857 to 4326
            SET @StartLng=(@StartLng3857*180)/@X

--converting the latitude from epsg 3857 to 4326
            SET @StartLat = @StartLat3857/(@X/180)
            SET @StartLat = ((ATAN(POWER(@e,((PI()/180)*@StartLat))))/(PI()/360))-90

It is a bit tricky to project EPSG 3857 coordinates to EPSG 4326 coordinate system. Microsoft recommends using ProjNet4GeoAPI so I decided to use that.

https://docs.microsoft.com/en-us/ef/core/modeling/spatial#srid-ignored-during-client-operations

I have verified that it works here:

http://epsg.io/transform#s_srs=3857&t_srs=4326&x=1530088.9600000&y=5085240.8300000

Example conversion:

var x = 1530088.96d;
var y = 5085240.83d;

var epsg3857ProjectedCoordinateSystem = ProjNet.CoordinateSystems.ProjectedCoordinateSystem.WebMercator;
var epsg4326GeographicCoordinateSystem = ProjNet.CoordinateSystems.GeographicCoordinateSystem.WGS84;

var coordinateTransformationFactory = new ProjNet.CoordinateSystems.Transformations.CoordinateTransformationFactory();
var coordinateTransformation = coordinateTransformationFactory.CreateFromCoordinateSystems(epsg3857ProjectedCoordinateSystem, epsg4326GeographicCoordinateSystem);

var epsg3857Coordinate = new GeoAPI.Geometries.Coordinate(x, y);

var epsg4326Coordinate = coordinateTransformation.MathTransform.Transform(epsg3857Coordinate);