s= 17. 3A GeV are described by a geometrical model (the participant-spectator model) and a thermal model (the thermalized cylinder model) respectively. The length of the cylinder formed in relativistic nucleus-nucleus collisions at a given energy does not depend on the centrality of collision. The normalized pseudorapidity distributions of photons emitted in different types of events with different centralities at a given incident energy are the same. The results calculated from the models are compared and found to be in agreement with the experimental data of the STAR and WA98 Collaborations.