Two pieces of same size are scanned into different mesh sizes. Why?

[Matse.P]

Hi guys,
I'm a photogrammetrical beginner but have a problem which I can't solve on my own.

I tried to scan two different parts of a front axle suspension. They're both the same size, only the construction revision differs a little bit.

Just have a look, I'm talking about these ones heres:



I know that the bore size of the clamp connection to the shocks is exactly 55mm of diameter.

My plan was to scan these parts, convert them to STL and reimport them in CATIA for example to compare some geometrical dimensions of these. But, when I was trying to, the size of the parts differs. The measurements of 3DZephyr are weired anyways, and as an STL-export, one part is much smaller then the other.

Which dimensions are the used measurement tools in 3DZephyr? Is it in inches? I measured internally in 3DZephyr a distance of 2,2, that would be nearly right in case of inches...

I used a Fuji X-T4 and just calibrated it inside 3DZephyr, source of the pictures is APS-C at 26MPixels from JPEG...

Can you please help me get to a reliable scan result which have the right measurements?

[cam3d]

Hi Matse.P

All 3D reconstructions made by 3DF Zephyr are subject to an arbitrary scale factor, a translation and rotation.

Units are also arbitrary, so they can be inches/mm/whatever your preference is:
To get accurate reconstructions you need to use control points for scaling (available in the Full Version of Zephyr):

https://www.3dflow.net/technology/documents/3df-zephyr-tutorials/tutorial-manage-control-points-distances-3df-zephyr/

You can achieve approximate scaling in Free/Lite:

https://support.3dflow.net/support/solutions/articles/43000052981-how-to-scale-and-make-measurements-with-zephyr-free-and-lite