BundleAdjustTwoViews scale ambiguity + BundleAdjustTwoViewsAngular usage

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Horst Wildenauer

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Sep 15, 2018, 4:41:14 PM9/15/18
to Theia Vision Library
Hello Chris,

I have two questions regarding your bundle_adjust_two_views implementation. Maybe you can help me out here.

.) BundleAdjustTwoViewsAngular implements Oliensis approach, which you seem not to use anywhere in your code. What are your practical experiences - is it performing worse than  BundleAdjustTwoViews in terms of accuracy?
.) Gauge freedom in BundleAdjustTwoViews: I cant find where you fix the scale of the problem. In the code I see that you fix the first camera, but cant see where the scale of the translation of the second camera is fixed. (You do this in
in BundleAdjustTwoViewsAngular)

I hope my questions arent too stupid. I have no working build (forced to use windows) and relied on just reading the associated Code.

Cheers and thanks in advance,

Horst
.

Chris Sweeney

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Sep 21, 2018, 3:16:24 PM9/21/18
to Horst Wildenauer, Theia Vision Library
Hi Horst,

I found that that angular approach did not work as well. I never dug into it too much.

The gauge freedom is not fixed in the 2-view bundle adjustment, but the translation is renormalized upon writing back out. This is because BA will take you to a local minima and so the translation will not drift too far away from unit-norm and it keeps the optimization simple. If the translation scale dramatically changes then the 2-view BA is not well constrained anyways and should not be used.

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Horst Wildenauer

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Sep 21, 2018, 8:55:28 PM9/21/18
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Hi Chris,

thanks for the info. I see your point regarding the local minima. How would you gauge what is too much change in scale?

Ps: In the meantime I coded both versions and my preliminary results confirm your opinion on Oliensis' Approach to be less accurate.

Cheers,
Horst
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