Photogrammetry Targets

Matthew Petroff — Sat, 26 May 2018 21:53:08 +0000

The Scanreference photogrammetry system includes 149 magnetic coded targets and PDFs for printing 192 more targets. However, while measuring something that isn’t ferromagnetic, the magnetic targets aren’t particularly helpful, and the 192 printable coded targets aren’t always enough. Unfortunately, AICON wouldn’t provide the full set of printable coded targets when I asked and instead tried to sell me a multi-thousand dollar software package for generating printable coded targets. Instead, I looked in the literature and found multiple references to a 1991 paper¹ as the original publication about the ring code targets. Unfortunately, the paper is not available electronically, so I had to request a copy via interlibrary loan; I received a copy just to find out that it didn’t include any technical details on the targets.

Fortunately, further research turned up expired German patent DE19733466A1. The patent contains all of the details needed to generate the ring codes for the coded targets, except for the exact parameters and numbering scheme used for the Scanreference targets. This missing information was fairly straightforward to figure out—the targets are 14-bit with no restrictions on the number of transitions from black segments to white segments and are ordered by increasing binary value. With this information, I was then able to write a script to generate the ring codes and a script to generate a set of printable targets, resulting in a PDF with all 516 targets ready to print on stickers.

Schneider, C. T. “3-D Vermessung von Oberflächen und Bauteilen durch Photogrammetrie und Bildverarbeitung.” Proc. IDENT/VISION 91 (1991): 14-17. ↩

coded targets – Matthew Petroff

Photogrammetry Targets