Precise, reliable photogrammetry models are a product of proper photography, targeting, and scaling. Algorithms within Photomodeler and iWitness identify contrasting circles. With this in mind, we designed custom targets for this project, with a one inch, white, retro-reflective circular center against a black background. In addition, fine guidelines were placed on the outer limits of the target to help ensure the target is placed in the right location (door line, body panel intersection, etc.). This pattern is printed on a strong 30 mil (0.03 inches thick) magnet to prevent any movement between photographs, yet the target is thin enough that the effect on the final model is negligible.
Additionally, we developed an original, retroreflective, spherical target that can be used with BOTH Photomodeler and iWitness. The spherical geometry allows the target to be selected from any angle, with essentially no error. Unlike spinner targets, no user input is required during the shoot, saving time and potential error.
The entire scale of a photogrammetry model is based on one control measurement, and for that reason the measurement is extremely important. With that in mind, we designed custom 48" scale bar comprised of black anodized aluminum, with two CNC-machined circles separated by 45" (+/- 0.005"). The bar is mounted on two aluminum tripods to increase stability, eliminating any potential movement between photographs. This precise scale bar ensures all measurements in the model are as accurate as possible.