Advice Needed: How to make a model of a long, thin object?

photogrammetry

(U Warchaeolab) #1

Hello everyone!

For the past year, our lab has been working on creating a 3D model of a large needle. The object is on a grid-marked, black turntable against a white or black backdrop. We have gone through 7 (soon to be 8) different attempts at running photo batches through Photoscan Pro, but all of the models we've produced have ended up either jumbled on the software, or with one or both ends hopelessly blurred and fused with the background.

We have tried:
-propping up the needle
-taking photographs of the front and back to merge later
-adding object markers to the field to help the program orient points

Does anyone have tips on how to successfully use photogrammetry to produce a model of this object? It seems that the main problem is managing to get the entire object into focus at once.


(Mesheritage) #2

Hello,

What is the size of your object?

Did you manage the get the sparse model of the setup without seeing the needle or even that part failed?

If you have an issue with focus, you can try focus stacking maybe. With some camera you can even do that automatically. Sometime it's a bit tricky, maybe better to avoid doing that too much but worth a try.


(Abby Crawford) #3

Hi @UWarchaeolab -

Have you tried masking the photos of the object that you're working on? I was working on a 3-4 foot long branding iron and had similar problems. I had taken a variety of photos, some up close and capturing just sections of the object, and others capturing the entire object in one shot. They kept getting jumbled and so I eventually broke down and spent the time masking them and when I went to process them again it worked like a charm. It's also important to use a high f-stop for your photos in order to keep as much of the object in focus as possible.


(U Warchaeolab) #4

Thank you for replying!

@Mesheritage
The needle is roughly 120 mm long, but only about 5 mm wide. We might try the focus stacking suggestion--most of the models we've created have excellent resolution on the middle portion of the object, but not for either of the ends. Could be something to do with the aperture on our camera/focus issues?

@abbyec
That's almost exactly the problem we're having (great model, by the way!). Masking 50+ photos will be time consuming, but we've already sunk so much time into this project anyway. It's definitely worth a shot, especially since it worked so well for you!

Will post updates as the project progresses.


(Mesheritage) #5

Indeed, when the apertures is larger, the object must be more "in plan". As you focus on the center and you might not be very perpendicular, the sides are blurry.
A way might be to have the smallest aperture but you need some extra light aside.

Regarding the advice of Abbyec, it is possible to automatically mask the entire 50 pics at once. At least if the background is clear and different from the object.
Also different software have various way for that. I remember it was quite fast on 3dZephyr but it was few years ago!

Good luck!