GiNGR: Generalized Iterative Non-Rigid Point Cloud and Surface Registration Using Gaussian Process Regression.

Link to the paper.

BibTex:

@article{madsen2022gingr,
  title={GiNGR: Generalized Iterative Non-Rigid Point Cloud and Surface Registration Using Gaussian Process Regression},
  author={Madsen, Dennis and Aellen, Jonathan and Morel-Forster, Andreas and Vetter, Thomas and L{\"u}thi, Marcel},
  journal={arXiv preprint arXiv:2203.09986},
  year={2022}
}

The GiNGR framework allows one to perform non-rigid registration with an iterative algorithm that uses Gaussian Process Regression in each iteration to find its next state.

Existing algorithms can be converted into the GiNGR framework and compared based on three properties:

1. Kernel function: how similar should the deformation of neighboring points be - this is determined based on their correlation.
2. Correspondence estimation function: how to calculate/estimate anatomically corresponding points between the moving instance (reference) and the target (e.g., use the closest point as a naive approach).
3. Observation uncertainty: what is the noise assumption of the correspondence estimations?

This framework contains a general library to input these three properties.

The core part of the GiNGR framework is found in gingr/api/GingrAlgorithm, with the update function performing one iteration of a GiNGR update. Different pre-implemented configuration files can be found under gingr/api/registration/config for the CPD and the ICP algorithms.

To use the GiNGR framework, you can make use of the maven repository version by including the following in your Scala 3 script:

//> using lib "ch.unibas.cs.gravis::gingr:1.0-RC1"

If using SBT, then add the following to your build.sbt:

libraryDependencies += "ch.unibas.cs.gravis" %% "gingr" % "1.0-RC1"

Or you can install GiNGR to your local repo (.ivy2) by running sbt publishLocal.

The examples can be run with Scala-CLI. To run the first tutorial, first CD into the example directory and run:

# scala-cli project.scala DemoHelper CreateFemurGPMM.scala

Alternatively, the examples can be run with the VSCODE IDE. For installation help, please see https://scalismo.org/docs/Setup/vscode.

After installing VSCODE:

• Go to the examples folder: cd examples
• Setup Code IDE with scala-cli setup-ide .
• Open the IDE with code .
• Now run the individual examples

To use GiNGR, one needs to specify the deformation model as a GPMM model, the correspondence estimation function, and the uncertainty update.

The creation of the GPMM is separate from the registration step. Look in the examples folder where demo scripts have been created to compute and visualize GPMMs for an Armadillo, Bunny and a Femur bone. The deformation model can be evaluated in the UI by sampling from it.

The next step is to define the correspondence and uncertainty estimation update. For this, default configurations have been implemented for CPD and ICP. Simple Demo applications can be found in examples/DemoICP and examples/DemoCPD

The demo scripts both perform deterministic and probabilistic registration one after the other.

In each iteration, a new GiNGR state is computed which contains the GPMM model, the current fit, the target as well as all the GPMM model parameters (non-rigid and global pose).

The probabilistic implementation is based on the ICP-Proposal repository: https://github.com/unibas-gravis/icp-proposal

The posterior output from the ICP probabilistic registration of the femur bone can be visualized with apps/registration/DemoPosteriorVisualizationFemur.

In examples/DemoLandmarks we compare 10 iterations of CPD for the Armadillo with and without the use of landmarks.

In examples/DemoMultiResolution we perform 3 different registrations of GiNGR one after the other. First CPD is used on a very coarse mesh (100 vertices), then CPD is used on a medium fine mesh (500 vertices) and finally, ICP is used on a finer mesh (1000 points) to get the fine details of the target mesh.

In the GiNGR code base, the basic implementations of existing algorithms can also be found for comparison. The algorithms are found under gingr/other/algorithms

Implementation of the CPD algorithm from https://arxiv.org/pdf/0905.2635.pdf

Implementation of the BCPD algorithm from https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8985307

Implementation of the non-rigid ICP algorithms from https://gravis.dmi.unibas.ch/publications/2007/CVPR07_Amberg.pdf