fitBsplineDisplacementField — fitBsplineDisplacementField • ANTsR

Fit a b-spline object to a dense displacement field image and/or a set of points with associated displacements and smooths them using B-splines. The inverse can also be estimated.. This is basically a wrapper for the ITK filter https://itk.org/Doxygen/html/classitk_1_1DisplacementFieldToBSplineImageFilter.html which, in turn is a wrapper for the ITK filter used for the function ANTsR::fitBsplineObjectToScatteredData

fitBsplineDisplacementField(
  displacementField = NULL,
  displacementWeightImage = NULL,
  displacementOrigins = NULL,
  displacements = NULL,
  displacementWeights = NULL,
  origin = NULL,
  spacing = NULL,
  size = NULL,
  direction = NULL,
  numberOfFittingLevels = 4,
  meshSize = 1,
  splineOrder = 3,
  enforceStationaryBoundary = TRUE,
  estimateInverse = FALSE,
  rasterizePoints = FALSE
)

Arguments

displacementField: input displacement field. Either this and/or the points must be specified.
displacementWeightImage: input image defining weighting of the voxelwise displacements in the displacementField. if NULL, defaults to identity weighting for each displacement. Default = NULL.
displacementOrigins: matrix (numberOfPoints x dimension) defining the origins of the input displacement points. Default = NULL.
displacements: matrix (numberOfPoints x dimension) defining the displacements of the input displacement points. Default = NULL.
displacementWeights: vector defining the individual weighting of the corresponding scattered data value. Default = NULL meaning all values are weighted the same.
origin: vector defining the physical origin of the B-spline displacement field. Must be specified if displacementField is not specified. Otherwise, the displacementField is used to define the domain parameters.
spacing: vector defining the physical spacing of the B-spline object. Defines the sampling rate in the parametric domain. Must be specified if displacementField is not specified. Otherwise, the displacementField is used to define the domain parameters.
size: vector defining the size (length) of the B-spline object. Note that the length of the B-spline object in dimension d is defined as parametricDomainSpacing[d] * (parametricDomainSize[d]-1). Must be specified if displacementField is not specified. Otherwise, the displacementField is used to define the domain parameters.
direction: matrix defining the orientation of the sampled B-spline object. Must be specified if displacementField is not specified. Otherwise, the displacementField is used to define the domain parameters.
numberOfFittingLevels: integer specifying the number of fitting levels.
meshSize: vector defining the mesh size at the initial fitting level.
splineOrder: spline order of the B-spline object. Default = 3.
enforceStationaryBoundary: ensure no displacements on the image boundary. Default = TRUE.
estimateInverse: estimate the inverse displacement field. Default = FALSE.
rasterizePoints: Use nearest neighbor rasterization of points for estimating the field (potential speed-up).

Value

ANTsR image.

Author

NJ Tustison

Examples


# Perform 2-D fitting

points <- matrix(data = c(-50, -50), nrow = 1, byrow = TRUE)
deltas <- matrix(data = c(10, 10), nrow = 1, byrow = TRUE)

bsplineField <- fitBsplineDisplacementField(
  displacementOrigins = points, displacements = deltas,
  origin = c(0.0, 0.0), spacing = c(1.0, 1.0), size = c(100, 100),
  direction = matrix(data = c(-1, 0, 0, -1), nrow = 2, byrow = TRUE),
  numberOfFittingLevels = 4, meshSize = c(1, 1)
)