{"ref":"refs/heads/master","commits":[{"author":{"name":"Nick Tustison","email":"325887eed19491791bd3d57950dce2026c525505@gmail.com"},"url":"https://api.github.com/repos/Kitware/ITK/commits/32be7d05c1893f60b44fc79217e26b81ab7abb7e","message":"ENH:  Registration method for time-varying velocity field transform.\n\nThis derived class from the SimpleImageRegistrationMethod class\nis specialized to handle time-varying velocity field transforms\nof which there are currently 2:\n\n1) TimeVaryingDisplacementFieldTransform\n2) GaussianSmoothingOnUpdateTimeVaryingDisplacementFieldTransform\n\nThe latter is derived from the former and performs an optional\nspatial and temporal smoothing on the update and total velocity\nfields. Integration of the velocity field is performed using\n4th order Runge Kutta and is performed using the class\nitkTimeVaryingVelocityFieldIntegrationImageFilter.\n\nOptimization occurs in an iterative fashion where for each\nsample time point, t, in the velocity field, we integrate\nthe velocity field in the range [0, t] to yield the\ndisplacement field which warps fixed image to time point\nt. Simultaneously, we integrate the velocity field in\nthe range [t, 1] to yield the displacement field transform\nwhich warps the moving image to time point t.  The metric\nderivative for each time point of the velocity field\ncalculated in this way produces the normalized update field\n(or gradient) of the velocity field to be added to the total\nfield at each iteration after being multiplied by the\nlearning rate and optionally smoothed.  Mathematically,\nthis can be described as\n\nv_{total} = G_1( v_{total} + \\lambda * G_2( v_{update} ) )\n\nwhere\n\nG_1 = gaussian smoothing on the total field\nG_2 = gaussian smoothing on the update field\n\\lambda = learning rate\nv_{update} = the normalized velocity field where we\nnormalize the velocity field at each time point\nseparately by the max norm of the field at that time\npoint. This is done due to a weakly necessary\n(but not sufficient) condition being that the velocity\nfield have a constant norm for all time points.\n\nChange-Id: Iaa8bdb743c4fdcb9138f5c59dc34487506836d13","sha":"32be7d05c1893f60b44fc79217e26b81ab7abb7e"},{"author":{"name":"Nick Tusison","email":"325887eed19491791bd3d57950dce2026c525505@gmail.com"},"url":"https://api.github.com/repos/Kitware/ITK/commits/35bfaba7eeca37bd074bb6e92699d681327e6ff2","message":"Merge topic 'VelocityFieldRegistration'\n\n32be7d0 ENH:  Registration method for time-varying velocity field transform.","sha":"35bfaba7eeca37bd074bb6e92699d681327e6ff2"}],"head":"35bfaba7eeca37bd074bb6e92699d681327e6ff2","size":2,"push_id":49671696}