best way to hold a parameter constant?

[Thomas Sharpless]

I have a cost function that depends on 9 camera parameters.  I would like to hold certain of those constant in some runs and let them vary in others.

Can this be done without rewriting the cost function?  If so, what is the recommended way?

I have already discovered that trying to alias parameter blocks does not work, ceres is too smart for that.

[Sameer Agarwal]

Use a SubsetParameterization.

Sameer

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[Pierre Moulon]

You can see an example usage here https://github.com/openMVG/openMVG/blob/master/src/openMVG/sfm/sfm_data_BA_ceres.cpp#L152

You define wich part of your parameter must remains const and it is done ;-)

Regards/Cordialement,

Pierre M

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[Thomas Sharpless]

SubsetParametrization would appear to be the right thing.  However when I do this:

    vector<int> sspv; // indices to hold constant

    sspv.push_back(8);

    if( sspv.size() > 0 ){

        ceres::SubsetParameterization cssp( 9, sspv );

        cprob.SetParameterization( cam2, &cssp);

    }

I get a runtime error: "pure virtual function called" when solve() tries to call cam2::LocalSize().  That is puzzling, as LocalParametrization.h seems to define that fn,

This with MSVC2013.

[Sameer Agarwal]

for one you are allocating on the stack and passing ownership to ceres, that seems like a recipe for trouble.

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[Thomas Sharpless]

Correct as usual, Sameer

This succeeds:

    if( sspv.size() > 0 ){

        ceres::SubsetParameterization *pcssp

            = new ceres::SubsetParameterization( 9, sspv );

        cprob.SetParameterization( cam2, pcssp);

    }

 

On Monday, February 22, 2016 at 11:49:08 AM UTC-5, Thomas Sharpless wrote: