I do repeat SfM surveys and would need fixed, stable points for registering the different epochs. Does anyone have some experience or could provide advice which targets (stable and fixable to rock, not printed on paper, potentially even attachable to a bolt) may be available for SfM, e.g. comparable to the CHI scale bars? I know of metal-based retroreflective circle-targets (Hubbs, but too small) or TLS-targets (e.g. tilt-and-turn targets of Leica, but very expensive and big) and also thought to let Agisoft-produced targets printed on alu-dibond. However, already manufactured tergets would be more convenient.