Fig. 1. (a) Principle of the reverse Hartmann test. (b) The measurement schematic of the PTC surface.

Fig. 2. Measurement of the PTC along the y direction. (a) One camera for half of the cylindrical surface, (b) two cameras for the entire cylindrical surface with small overlapping zones, (c) three cameras for the entire cylindrical surface with sufficient overlapping zones, and (d) the measurement schematic of the PTC surface along the y axis.

Fig. 3. Slope stitching configuration for acquisition sections of three cameras.

Fig. 4. Iterative process for 3D shape reconstruction of the collector.

Fig. 5. Southwell integration for surface shape reconstruction.

Fig. 6. Schematic of the experiment setup for using the reverse Hartmann test to measure the large collector.

Fig. 7. (a) Experimentally measured slope deviations for three cameras on the x axis, (b) experimentally measured slope deviations for three cameras on the y axis, (c) stitched gradient data and height deformation, and (d) slope distributions and 3D shape of the PTC.