scott_f Asks:

I am using Proj4Net to convert between coordinate systems. I’ve noticed that when I convert from one coordinate systems (CRS) and them back to the original CRS, the coordinate Y values have changed when I convert back to the original CRS.

*Converting to a CRS and the back to the original CRS, not the same original coordinates*I am using Proj4Net to convert between coordinate systems. I’ve noticed that when I convert from one coordinate systems (CRS) and them back to the original CRS, the coordinate Y values have changed when I convert back to the original CRS.

E.g. Original **EPSG 2105** X: 372893.221 Y: 809590.**1314**

Convert to **EPSG 3857**: X: 19420845.9813353 Y: -4410280.07002807

Convert back to **EPSG 2105** X: 372893.221025973 Y: 809590.**123207413**

I have since used several different EPSG values with the same sort of results.

Its always the coordinate **Y values** that are distored from the original.

The coordinate **X values** seem to convert relatively correctly.

Here is the code from my method that converts between CRS:

Code:

```
var cs_from = SridReader.GetCSbyID(from_epsg);
var cs_to = SridReader.GetCSbyID(to_epsg);
var ctfac = new CoordinateTransformationFactory();
var trans = ctfac.CreateFromCoordinateSystems(cs_from, cs_to);
//=============================================================================
var from_TopLeftCorner = new double[] { bbox_from.Min_X, bbox_from.Max_Y };
double[] toTopLeftCorner = trans.MathTransform.Transform(from_TopLeftCorner);
//=============================================================================
var from_BottomRightCorner = new double[] { bbox_from.Max_X, bbox_from.Min_Y };
double[] toBottomRightCorner = trans.MathTransform.Transform(from_BottomRightCorner);
var converted_bbox = new BoundingBox_Model
{
Min_X = toTopLeftCorner[0],
Max_Y = toTopLeftCorner[1],
Max_X = toBottomRightCorner[0],
Min_Y = toBottomRightCorner[1]
};
```

Is this behaviour expected or am I doing something wrong?

As I am inserting the image to use for GIS the image’s location needs to be extremely accurate.

Is this possible when converting between CRS?

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