iPad launch orientation when flat on surface

I have the following code:

 -(void)viewWillAppear:(BOOL)animated {

    UIDeviceOrientation orientation = [[UIDevice currentDevice] UIInterface];

    if(orientation==UIDeviceOrientationLandscapeLeft || orientation==UIDeviceOrientationLandscapeRight) {
        NSLog(@"Device Landscape");
    } else {
        NSLog(@"Device Portrait");
    }

 }

This works perfectly for the simulator and on the device but only if the iPad is not flat on a surface, for example if i lay the iPad on my desk and load the view it will say its portrait and so I cant detect the orientation when the view appears.

Any ideas of the best way to detect the interface orientation when the viewWillAppear is called?

Thanks