Hi @stratus, It would help in beginning to appreciate the difference between a gaze point and fixation point.
In simple terms, a gaze point is the point on the screen where the user is looking at a given moment of time. However, because the gaze point is an intrinsically noisy signal, the GazePointDataStream uses a configured filters to stabilize the signal.
Whilst fixations are determined as from a series of gaze points: one point representing the beginning of the fixation, a set of intermediate points during the fixation and the last point corresponding to the end of the fixation. As with the GazePointDataStream, the fixation stream will also have a unique filtered applied.
Accordingly, whilst one might expect the location of Gaze Point and Fixation to be similar within a short time period, they will never be exactly the same.
There is a great deal of documentation available online that goes into further detail on this topic. One such link with good depth can be found @
https://www.tobiipro.com/learn-and-support/learn/eye-tracking-essentials/types-of-eye-movements/
Regarding the use of C++, Whilst we have plans to add C++ bindings to Core SDK Interaction API in the near future, but currently the only option is to use stream engine API (http://developer.tobii.com/tobii-core-sdk/) or the legacy EyeX SDK.