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raulmur / ORB_SLAM2

Real-Time SLAM for Monocular, Stereo and RGB-D Cameras, with Loop Detection and Relocalization Capabilities
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Why is there no linearizeOplus() method in class EdgeSim3ProjectXYZ? #440

Open highlightz opened 7 years ago

highlightz commented 7 years ago

I think g2o optimizer needs the Jacobian of residual with respect to Vertex in order to perform an optimization, but in file types_seven_dof_expmap.h, class EdgeSim3ProjectXYZ has no Jacobian definition. Can anyone understand this?

AlejandroSilvestri commented 7 years ago

@highlightz ,

I'm not sure if I understood you correctly, but I try an answer.

EdgeSim3ProjectXYZ is a child class of templated BaseBinaryEdge class, which implements a virtual linerarizeOplus. This method is inherited by EdgeSim3ProjectXYZ: there is a linerarizeOplus in EdgeSim3ProjectXYZ, an inherited one.

g2o calculates the Jacobian using linearizeOplus.

I quote g2o's manual, in 6.1: "It offers for free the calculation of the Jacobians, via an implementation of the linearizeOplus method."

Again, I'm not sure if this is what you ask.

highlightz commented 7 years ago

@AlejandroSilvestri This is exactly what I need to know, and thanks for your explanation. So this is my understanding: since we do not provide a linearizeOplus method, no analytic derivatives are provided, instead, the optimizer uses the automatic derivatives from base class linearizeOplus. Am I correct?

AlejandroSilvestri commented 7 years ago

@highlightz ,

That's correct!

g2o has many base template classes, as helpers for specialization programmers should do.

But it also has a lot of very common specializations already implemented. EdgeSim3ProjectXYZ is one of them. If I remember correctly, orb-slam2 doesn't implement any specialization, it only uses those already provided by g2o.

highlightz commented 7 years ago

@AlejandroSilvestri Thanks again.