is photogrammetry practicable for factories?

[philsogood]

hello

i'm a drafter and i work as a freelance (since 1 week)

some of my competitors have scanner(s) to create cloudpoints for revamping some workshops/factories

as i have only few money yet, i can't buy a scanner (25-30k€) so i thought photogrammetry could be a solution. last year during the lockdown i did few tests on a parking area, outdoor, and i works not so bad (i used metashape)... these were my first shots. this week i tried to do the same exercice indoor and the result is definetly poorer! well my camera is a old one (Nikon D80) but it's not a bad reflex with a quite good lense...

not sure  that i can have result usable, with enough precision to be able to work with for my job

if anyone have any feedback about photogrammetry for that kind of use, you're welcome!! :)

Phil

[Dave Martin]

Phil,

I have captured room-sized interior spaces, but haven't imaged or scanned a factory as such; so these are a few generic thoughts, and much depends on the context, and what your deliverables are.

If it is a factory occupied by equipment, pipes, ducting, conveyors, etc. then it is difficult for both laser scanners and photogrammetry as there will be numerous areas which are occluded (hidden) behind/above/below obstructions, so you'll only be able to capture the nearest face. Photogrammetry can struggle more because the processing software needs to 'see' and 'recognise' something in multiple images. With a laser scanner (at sufficient point density) you can pick up, say, a number of points on the nearest faces of say a duct, sufficient to estimate its diameter or section. Furthermore, you only need space for a single laser shot to get 'between' two items to capture at least a point behind - whereas with photogrammetry to derive that point you need it in at least two images, ideally more, and if you move viewpoint to take the next frame, you may lose sight (and even if you can see it, is there sufficient to triangulate its location?).

If it is an empty space, then that is probably more achievable with photogrammetry subject to two factors - illumination and detectable tie points. In small rooms or ships' compartments for example, a ring-flash can be a useful illuminator; but for a cavernous space you will be dependent on existing lighting so you may be advised to use a tripod (so as to have as long an exposure as you can) and shoot from camera stations. Also in a cavernous space, especially if uniform, you may have difficulty when processing in establishing sufficient number and quality of tie points between your images so use of targets (ideally coded) would be worth considering - you could also use them as scale-markers.

Although there may be some in the Cultural Heritage world who have imaged/scanned factories or comparable spaces, I would suggest that it might be productive for you to pose your query in more generic fora such as Agisoft's own forum, or FaceBook groups such as that dedicated to MetaShape or the generic 'LiDAR and Photogrammetry Review'.

Dave