The order got broken when Brown distortion model has been added.
Made it so the indexing of parameters is strictly defined in the
parameter block, matching how parameters are used in the cost
function.
There is some duplication going on accessing parameters. This can
be refactored in the future, by either moving common parts packing
and cost function to an utility function in bundle.cc.
Alternatively, can introduce a public PackedIntrinsics class which
will contain a continuous block of parameters, and each of the
camera models will have API to be initialized from packed form and
to create this packed form.
The benefit of this approach over alternative solutions previously
made in the master branch or suggested in D9116 is that the specific
implementation of BA does not dictate the way how public classes need
to be organized. It is API which needs to define how implementation
goes, not the other way around.
Thanks Bastien and Ivan for the investigation!
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