To make coincide the window's viewer default and ofcamera::lookat

I would like to make coincide what I look at through ofx window without a camera with what I look at through the camera using lookAt.

Actually, I would like to know what are the coordinates of the window’s viewer default to set on ofcamera::setposition() and ofcamera::lookat()

At the moment :
I put a 3D model with ofxassimploadermodel on (ofGetWidth() / 2, ofGetHeight()/2, 0)
I set my camera cam : cam.setPosition(model.getPosition().x, model.getPosition().y, 500);
I look at : cam.lookAt(ofVec3f(ofGetWidth() / 2, ofGetHeight()/2, 0), ofVec3f(0, -1, 0));

-1 instead of 1 because with 1 my view is reversed (I don’t know why…) but the interaction like add a object on (mouseX, mouseY, anything) with the mouse doesn’t put on in my view cam.

Best regards