Interested how it's work ?
What is photogrammetry:
Photogrammetry is the science of making measurements from photographs. It infers the geometry of a scene from a set of unordered photographs or videos. Photography is the projection of a 3D scene onto a 2D plane, losing depth information. The goal of photogrammetry is to reverse this process. - https://alicevision.org/
Two general types of photogrammetry exist: aerial (with the camera in the air) and terrestrial (with the camera handheld or on a tripod). Terrestrial photogrammetry dealing with object distances up to ca. 200 m is also termed close-range photogrammetry. Small-format aerial photogrammetry in a way takes place between these two types, combining the aerial vantage point with close object distances and high image detail. - James S. Aber, ... Johannes B. Ries, in Small-Format Aerial Photography, 2010
In practice it's essential to capture as many pictures as needed to "see" that object from various angles - photogrammetry software works like our brain, If we see mug from all angles, we can recreate it shape in our heads, but without knowing how the bottom looks like, it is impossible to predict what is there (maybe crack? maybe small hole?). The most common technique is creating pictures every 10 degrees from at least 3 different levels + picture sessions for the top and bottom part of the object.
What is needed to create the best possible model:
- a solid amount of pictures - for smaller objects around 200 is enough, but for the biggest recorded project (city center with few roads) counted above million photos
- good understanding of photogrammetry technique limitations - surfaces with lack of information like single colored plastic, shiny metal surfaces and translucent material like liquids, glass and crystals are usually impossible to capture without good planing and light operation or additional items like mate spray (dust, shoe spray, chalk, etc. )
- high-quality hardware - to capture highest possible quality picture set (not affected by picture noise, blur, lack of depth of field) with correctly captured light color information, knowledge about photogrammetry software and other programs for additional works like scan clean up from surface noise, hand details recovery in case of missing picture information
- presentation of the object (creating additional model information's about surface (that part is metal, that one is plastic, good light presentation, animations )
How long take to recreate model:
Photogrammetry recreation is a really complex procedure. Most critical elements that give a visible change of recreation time are
- amount of pictures (that why it's better to spend an additional 10 minutes and plan photogrammetry capturing session than wait extra hour during input base processing)
- size of pictures
- computing power (simple model can be recreated on ~1500 euro machine, but more complex require hardware worth couple thousands or even rent of external processing farm )
- used software
From my experience, to just recreate a single model, it's needed around 12 hours of work. If a model requires additional things like cleaning up (a bad light condition during capture session or outsource material provided by client from example drone or scanned model) or presentation, it's safe to say that a single model can take up to 3 working days to show full potential.
Bigger or more complex projects like temple entrance or similar things can extend recreation time itself to even days. Project "Mesa Verde" https://jurandm.artstation.com/projects/XBLqo0?album_id=1762840 (2080 pictures) take me a week to just generate RAW scan model.
