Advice on starting photogrammetry


(Cderolin) #1

Hi,

I'm thinking of trying photogrammetry. I'm spoiled at work as we have two Artec scanners and even access to a micro ct. but I'd like to do some scanning at home in my own time, so looking for a cheaper solution (around £500). I'm thinking photogrammetry might give better results than a cheap scanner? I currently only have a camera on my iPhone 6, so wondering what camera / lens would be a good purchase? I'm looking at either a Nikon d3300 or d5300, which comes with a 18-55 lens. Does anyone have any experience of using these for photogrammetry, or is there another you would recommend? I'm interested is scanning small things (big insects, animal skulls etc) so maybe a macro lens too?

I have the standard Agisoft Photoscan software and Autodesk remake educational license. I was wondering what people's experience with these is or if there is another software worth considering?

Any thoughts or suggestions on the best kit to start with would be much appreciated. Many thanks in advance.


(Ondaka) #2

A d3300 or d5300 will work just fine. Just remember to shoot in manual, keep the focus locked, ISO100'sh, shoot in the correct lighting, and you should be fine. Make sure you have 25-50% overlap on photos. More photos doesn't always mean better results. The correct shots = better results.

I'd skip photoscap and recap personally. I've had better results with RealityCapture.


(F1xer) #3

I've used VisualSFM/Meshlab on a mac after watching Youtube (3D scanning for free).
I've done some large subjects but nothing small as yet.
I can imagine you'd need a turntable for the subject and a tripod to fix the camera positions to make sure the movement was evenly spaced. You could save money for these items by using an extension ring or a reversing adapter with the standard lens rather than an a dedicated macro lens. With large subjects I've found that many lower quality shots overlapping by more than 50% gives more consistent results.


(Nate Sid) #4

I use a D5300 for most of my scans, using the 18-55 kit lens for my outdoor/large subject scans (a 85mm macro lens is used for subjects that are fist sized and smaller).

The 85mm macro lens seems to work pretty well for most of the mineral scans I do, but i have had some trouble scanning smaller specimens (like rat mandibles and smaller mineral specimens).

Zircon Crystal: 1.5cm long

Rat Mandible: ~1.7cm long

It would be worth considering image stacking software (like Helicon Focus) if you plan to scan things like insects (unfortunately, i don't have a great deal of experience with image stacking software since i haven't needed to use it for any of my scans so far).

@nebulousflynn has done some great insect models ( https://sketchfab.com/nebulousflynn/collections/zoosphere ), and if you go to the zoosphere website, they give a very brief overview of the workflow involved in terms of photograpghy: http://www.zoosphere.net/project.

I'd imagine the photography stage for something like this to be incredibly time consuming, since you'd be wanting at least 100 images of your specimen (minimum) from enough angles to ensure complete coverage (and each of those 100 images will be the product of 5 or more images processed in Helicon to produce 1 in focus image).

As @russsm and @f1xer have pointed out, using a turntable and a tripod are definitely a must if you want to do complete scans of smaller subjects, and the camera settings are very important too. My go to settings are typically

ISO: 100 (bumped up to 200 for darker subjects, like coal)
F-stop: ~32 ( not sure if this too high)
Exposure time: 3 sec
I use the ceiling lights in the lab I work in because they seem to provide even, flat lighting for my subjects
The turntable is marked at 20° intervals to ensure i take my photos at even spacing and have sufficient overlap (although you need less photos as you photograph your subject from higher angles https://skfb.ly/TDtM)
A sheet of white card-stock is used for a backdrop which seems to remove the need for image masking.

I scanned this specimen at home using a lazy susan as a turntable with a white card-stock backdrop, the 18-55 kit lens, and natural lighting (under the veranda in my backyard). The specimen was roughly 15cm x 7cm x 5cm.

So you can get away with a pretty budget setup in some cases (excluding the DSLR, and processing computer, which aren't exactly 'budget' :stuck_out_tongue: ).

I've had pretty good results with Agisoft Photoscan Professional, but RealityCapture seems to be a lot faster in terms of processing time, and handles finer details better (like tree branches and foliage, or spines on certain creatures). I have heard that it has some issues aligning photos from turntable scans though. You can get a 3 month RealityCapture license for €99, or €15,000 for lifetime access, just in case you feel like taking out a small mortgage...


(Egiptologo91) #5

All my models are made using a Nikon D5300 with a Sigma 18-300 lens.


(Vegaprint) #6

all models are well design. Its D5300 shots