I have imported a 3D scene (.pvc) carried out with PVCase. The solar field has 372 trackers and the 3D scene imported is been scomposed in 372 objects named ''tracking field #xxx''. I had thought that what I did was all right to launch the calculation of the shading scene with the option linear shadings. I was a little bit surprised when PVsyst shown me the following alert: ''The backtracking strategy is based on distance and width of trackers. Therefore you should define at least one subfield with several trackers. Please correct the shading scene.'' My question is: why PVsyst ask me to define at least one subfield with several trackers when all these informations are defined in the imported 3D scene of all the PV field (orientation, dimension, pitch, quantity of the trackers). Based on the above, what is the correct procedure to carrried out the calculation of the linear shadings? Thanks in advance Sergio