A novel capacity expansion and recognition acceleration method for dot-dispersing coded targets in photogrammetry

In close-range photogrammetry, some improved designs have been developed to increase the coding capacity of Schneider-like concentric circular coded targets. However, another typical type, Hattori-like dot-dispersing coded targets (HCTs), is rarely expanded. In this paper, we give our detailed solution to recognize a kind of non-public HCT used in video-simultaneous triangulation and resection systems. Then, an advanced HCT (AHCT) with multiple templates and simplified P-2-Invariant is proposed, which achieves capacity expansion and recognition acceleration. First, the cross-ratio invariant is used in template recognition, and then the affine transformation is used in decoding. During the template recognition process, multiple templates are designed to expand the coding capacity, and a simplified P-2-Invariant is adopted to accelerate the recognition. Experiments are carried out with different shooting angles ranging from 0 degrees to 80 degrees, with smaller coded targets, with mixed coded targets of different sizes and with large outdoor scenes, and the results show that AHCTs can not only preserve the stability of the HCTs, but also achieve the capacity growth of coded targets at a faster recognition rate by 14.6%. The AHCTs with large capacity can be applied in scenarios with a large size or complex structure, and the acceleration advantage can be considered in real-time dynamic domains.