[pnelsonAG]

In my original question I said,

"I also tried adding to the MouseCameraController . . .

Code:

Code:

EventsSourceElement="{Binding ElementName=MainViewport}"

...or...
Code:

Code:

EventsSourceElement="{Binding ElementName=ViewportBorder}"

... just because they're in your Polyline example, but I don't really understand it and neither one helped."

... how is this different from what you suggested?