Hi Sai,
the gaze coordinates will be outside the range [0, 1] if the gaze is outside the viewport (the human gaze doesn’t care about viewport boundaries!). You can of course clamp them if you want them to always be within range.
The EyeXGazePointDataStream returns EyeXDataPoint.Invalid — where X and Y are both NaN — until the stream has been started and the first data point received from the EyeX Engine. So you need to check for invalid data before passing it into the rotation calculations.