external drawing pad as mouse device: flip portrait - landscape

I have an external drawing pad (digimemo l2) that's recognized as a mouse device and works fine with xournal. My only problem is: it assumes landscape. How can I switch to portrait? (I am running xubuntu 16.04.)

You can set the Coordinate Transformation Matrix for your tablet using xinput. See this page in the Ubuntu Wiki for the details.

Holger

Thank you, the page from the Ubuntu Wiki was exactly what I needed.