*3.5. Re-Topology*

Coinciding in time with the work presented in this article, but more diligent in publishing their results, the text 'New realities for Canada's Parliament: A workflow for preparing Heritage BIM for game engines and Virtual Reality' [17] already explains clearly and sufficiently the importance of re-topology in the processes of building 3D models and, therefore, in photogrammetry projects. It does not deny that it could always have been photographed better and more effectively and, as is proposed in the mentioned research, that it would have been helpful to have a previous understanding of the script with respect to the points of most interest to the viewers, in order to make decisions during the data capture and processing that would have helped in the composition and the rendering.

Without going into the depths of the analysis, the 3D models that were directly produced by the data from photogrammetry platforms far exceeded the dimensions that were manageable by graphics cards and processors, however powerful they may have been, and yet such a profusion of data does not result in improved accuracy or fidelity, nor photorealism, as we have seen. An intermediate process, re-topology, is necessary to simplify the models, retouch possible occlusions or imperfections and produce textures that, once back-projected onto the new model, allow greater detail that is more similar to the real scenarios, and much greater fluidity in the interaction with the scenes.

The specific issue of viewer interaction with the scene also needs to be addressed, as there are specific methods that can improve the performance of the platforms. At the end of 2015, Nick Kraaman explained in his Headjack blog [51] the progress made by different professionals to develop scenes in which viewers would be immersed and equipped with HMD. One of the points made was the possibility of covering up areas of inactivity with static images instead of video, which would make interaction in the other areas much smoother and take up far fewer system resources.

There is no doubt that platforms will continue to improve, as will hardware devices, and it is clear that, by knowing the geography of the scene well and foreseeing the points of greatest interest, it will be possible to make better use of resources.
