What happens to coordinates after setting ofxOrientation?

I tried setting the orientation to left in my setup function and I’m trying to understand what’s happening then. The image I add afterwards is rotated correctly but the coordinates act weird: when I set the position of my image to 0,0 it looks like this… so it’s not at 00 in any way. so my question is:
what happens to coordinates when rotating using ofSetOrientation(OF_ORIENTATION_90_LEFT);?

(I’m on iphone5 with ios 8.3 and xcode 6.3 if that affects the answer…)