I’m using NetTopologySuite 2.5.0. I have a Geometry, say a Point at (1.57554173300002, 42.646007512) with an SRID of 4326.

I would like to change the SRID to 3857, so a Point at (175388.50344111404, 5258244.862258436).

However, when I change the SRID to 3857, the new Point has the correct SRID but the Point hasn’t changed. I have the same behavior with (Multi)Polygons as well.

Am I not creating/reassigning the SRID correctly? Does the GeometryFactory require a different/additional step to do this? I know many change the SRID for their Geometry objects so I expect many have solved this already. Thank you in advance.

Example 1, changing SRID directly

const double inputX = 1.57554173300002;
const double inputY = 42.646007512;
var point = new Point(new Coordinate(inputX, inputY))
{
   SRID = 3857
};
Console.WriteLine($"x = {point.X}, y = {point.Y}");
// Prints "x = 1.57554173300002, y = 42.646007512"

Example 2, using GeometryFactory

const double inputX = 1.57554173300002;
const double inputY = 42.646007512;
var factory = new GeometryFactory(new PrecisionModel(), 3857);
var point = factory.CreatePoint(new Coordinate(inputX, inputY));
Console.WriteLine($"x = {point.X}, y = {point.Y}");
// Prints "x = 1.57554173300002, y = 42.646007512"