The work presented in this paper details an original procedure developed in order to automatically build on-cam surfaces for double-regulated hydropower units such as Kaplan or bulb turbines. The proposed method allows a sparse exploration of the operating domain to identify cam points of the machine. The automated approach enhance the reliability of performance hill charts obtained from simulation or model testing. The software implementation of the method is described, together with its application to the case of Priest Rapid hydropower plant.