Multiple EvaluationCallbacks?

[Giorgio]

Hi, 

I am working on a large bundle adjustment problem using ceres and would like to add multiple instances of evaluation callbacks to the problem.
Is that possible? 

Thank you for your help!

[Sameer Agarwal]

No we only allow one evaluationcallback. But that mechanism should allow you to chain things any which you want. 

What's the use case for multiple independent evaluation callbacks?

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[Giorgio]

thank you for the reply, Sameer. I am implementing some error terms that have a residual relating to a feature observation by multiple poses (so n poses have a shared residual but different jacobians). For simplicity, I wanted to have one evaluation callback computing the residual for every individual feature. 

I fixed this by just looping over all features inside the single evaluation callback. 

[Giorgio]

Hi Sameer, 

I am trying to debug my jacobian computation and would like to use the gradient checker. For this, I understand I need to compute the residuals inside of the evaluate function (I currently precompute the residuals in the EvaluationCallback). 
Intuitively, I was tempted to call PrepareForEvaluation inside of the Evaluate function for every error term and to then turn on the gradient checker. This does not work: my residuals are evaluated as -nan if I call PrepareForEvaluation in Evaluate. 

I suspect this is due to the residual being a function of all the parameters in the problem. 

Is there a better way debugging my jacobians with autodiff?

Thank you!

[Sameer Agarwal]

The simplest thing would be to wrap your computation inside a costfunction and check it.

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