Hi @dragonus, thanks for your message.
The tobii_calibration_stimulus_points_t is in fact declared within Tobii.StreamEnginePartner.Interop.cs which is part of a partner package that is provided for specialised clients who have signed an NDA with Tobii.
The ability to use tobii_calibration_stimulus_points_t is part of a the custom calibration package within the Stream Engine.
If you feel you require this functionality, and would like to request a quote please let us know.