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Author Topic: Scaling consistency?  (Read 3892 times)

snapper

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Scaling consistency?
« on: May 30, 2014, 03:17:55 AM »
Hello There!

If I use PhotoScan Standard to create a series of models - all taken with the same camera, lens, working distance, focal length - can I assume that the scale factor applied by PhotoScan will be consistent for all the models?

I’m wondering how PhotoScan scales. The models are for scientific research and the client wants to compare the relative shapes and sizes. The actual amount of scaling is less important than knowing that the scaling is consistent across models.

Anyone know! Thanks

Marcel

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Re: Scaling consistency?
« Reply #1 on: May 30, 2014, 09:32:58 AM »
The scale and orientation will be random, unless you have the Professional version of Photoscan and you use 'markers'.

You could also add an object with a known size in your scan (a stick or a ruler) and scale each model to the same size.

Kiesel

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Re: Scaling consistency?
« Reply #2 on: May 30, 2014, 06:37:02 PM »
Hello marcel,

you can do it with the standard version and a third party program like Meshlab as well, but not as acurate as in PhotoScan (PhotScan Professional/Education is more acurate because you can measure your distance in photos and not in the mesh.):

1. Add a stick or a ruler with a known distance to your subject
2. Process as normal in PhotoScan
3. Export your ready processed mesh

In Meshlab:

1. Load your mesh in Meshlab
2. Measure the ruler/stick with the measure tool (measuring tape - symbol). You get your distance in model system.
3. Calculate the scale (known distance divided by measured distance)
4. In Meshlab go to filters "Normales, Curvatures and Orientation" then "Transform: Scale"
5. Put in your scale in the fields for Y, X and Z hit "Apply" and "Close"
6. Control the scale by measuring the known distance again.
6. Save your scaled mesh.

Cheers,

Karsten

Marcel

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Re: Scaling consistency?
« Reply #3 on: May 31, 2014, 02:17:12 AM »
Thanks Karsten,  that is really good to know, very useful!