Convert Pixels to CM in WPF

Question

I have

?(New System.Windows.LengthConverter()).ConvertFrom("1cm")
37.795275590551178 {Double}
    Double: 37.795275590551178

So, in 1cm I have 37.795275590551178px WPF pixels.

My problem is how I convert back from px to cm?

Answer 1

As in WPF we deal with DeviceIndependentUnits (DIU, named, conventionally "px"), that units does not depend of the device or screen resolution.

Actually the factors used in .NET Framework (4), for 'px', 'in', 'cm' and 'pt' respectively

// System.Windows.LengthConverter
private static double[] PixelUnitFactors = new double[]
{
    1.0,
    96.0,
    37.795275590551178,
    1.3333333333333333
};

So, we have

private struct PixelUnitFactor
{
    public const double Px = 1.0;
    public const double Inch = 96.0;
    public const double Cm = 37.7952755905512;
    public const double Pt = 1.33333333333333;
}    

public double CmToPx(double cm)
{
    return cm * PixelUnitFactor.Cm;
}

public double PxToCm(double px)
{
    return px / PixelUnitFactor.Cm;
}