Getting a useable cropped content with zero transform and correct size in UWP XAML

croppedImg.xaml

<!--
Full is your viewmodel containing the whole of your content (whatever control, here as an example an image)
Part is your viewmodel containing the area to crop
Part has a clipping rect, and 2 offset (OffsetX and OffsetY) why are basicaly -Rect.X and -Rect.Y. This puts the cropped part
on the top left of the grid and allow natural clipping through its render

protip : surround with a ViewBox if the size needs to be fluid in your UI
-->
<Grid Width="{Binding Part.Rect.Width}" Height="{Binding Part.Rect.Height}">
    <Grid Width="{Binding Full.Width}" Height="{Binding Full.Height}">
        <Grid>
            <Grid.Clip>
                <RectangleGeometry Rect="{Binding Part.Rect}"/>
            </Grid.Clip>
            <Grid.RenderTransform>
                <TranslateTransform X="{Binding OffsetX}" Y="{Binding OffsetY}"/>
            </Grid.RenderTransform>
            <Image Width="{Binding Full.Width}" Height="{Binding Full.Height}" VerticalAlignment="Top" HorizontalAlignment="Left"/>
        </Grid>
    </Grid>
</Grid>

rekt