PeachDrawing.Win2D.Win2dCanvas
Win2dCanvas.TransformScale Property
How much the transforms pushed so far magnify a unit along each axis: the lengths of the images of the unit x and y vectors under the accumulated linear part. A raster region renders at the physical resolution the document asked for <em>after</em> those transforms are applied, so it needs this to pick its pixel pitch; a graphics that does not track transforms reports no magnification.
public override (double X,double Y) TransformScale { get; }