Hi Hanju,
By design, the Tobii EyeX SDK does not provide the possibility to customize calibration since all the eye tracking groundwork such as hardware configuration, calibration and gaze data processing is taken care of by the EyeX Engine. This means that multiple eye-gaze enabled applications can co-exist nicely and that the user experience for the end user will be consistent across all applications, and the end user only have to calibrate once.
For single-application environments with special demands such as custom calibration, the Tobii Gaze SDK can be used. The Gaze SDK is a low-level API which give you full control but also full responsibility to implement everything yourself (such as hardware configuration, calibration and gaze data processing).
If all you need is a stream of gaze data in a single-application environment with a customized calibration, maybe the Gaze SDK is the best match.
If you want to have the best from both worlds, that is possible too. You can use the Gaze SDK to implement a custom calibration procedure, and then let the rest of the eye-gaze interaction be based on the high-level EyeX Engine API.
/Jenny