A system may include a sensor comprising a sensor configured to capture data from a part of an engine. The system being configured to form a three-dimensional (3D) surface model of the part of the engine based on signals received from the sensor system, determine a nonplanar reference surface based on the 3D surface model of the part, and measure a characteristic of a damaged portion of the part of the engine based on the 3D surface model and the nonplanar reference surface.