Hi @thibaut, The production of heatmaps necessarily require the long term storage of gaze data which as you probably know is contrary to the Tobii Core SDK licence agreement, so there will be no provided software from this end.
If however, you have an agreement with Tobii to use the Tobii Pro SDK with the C4, then you may have better luck as a number of third party software packages are available online (I saw a few from google) which take a variety of input data such as tracking data, GPS, etc and from there create heatmaps.
One such example I found for you is available @ https://github.com/sethoscope/heatmap