Jim,
You are exactly correct. In fact, the best results are achieved with "pre-targeted points" in which reflector tape is placed at all salient points. Each point must be imaged on at least three photos to have any sort of accuracy statistic computed, and best results are from points imaged on about 6 to 9 different images. For "topo" applications, it's mostly useless unless you can pick out discrete identifiable points such as rocks or distinctive pebbles. Photogrammetry works, but it's still dependent on geometry. Hardest thing to achieve is good results from non-targeted points. Pray for rivets or corners with sharp edges, and lots of them.
Isn't a lot of this pre-targeting being replaced with pixel pattern algorithms?
Very problematic with highly convergent imagery due to different angles of illumination. Tends to work well with vertical aerial photography, less so with terrestrial or low-altitude convergent photography, especially if there is significant depth in the subject volume as a proportion of the camera-to-object distance. Works nearly perfect with flat desert areas. 🙂
> Isn't a lot of this pre-targeting being replaced with pixel pattern algorithms?
as i recall, Datumate has computations for both relative pixel to coordinate transformations and absolute pixel to coordinate. with the proper combination of imagery, laps, and measurements, a model can be generated in absolute coordinate systems
I saw a demo of Datumate. My mind raced with the possibilities. Reading these posts makes me realize that the usefulness of this possible tool in one’s kit is the applications of the tool. We model a lot of intricate structures. Lattice electrical towers, monopole electric towers, substations and power plants. These features might be the ideal target for this application. I hope so. I am investigating the technology along with drone-based cameras to capture the images. Flying a quadcopter around high-voltage transmission lines might be a shocking experience. 😉