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Read ANTs transform file

Source: R/as_ieegio_transform.R
io_read_ants_transform.Rd

Reads spatial transformation files in ANTs (Advanced Normalization Tools) format, including affine matrices (.mat) and deformation fields (.h5, .nii.gz).

Usage

io_read_ants_transform(
  file,
  space_from,
  space_to,
  interpretation = c("passive", "active")
)

Arguments

file

character string specifying the path to the transform file. Supported formats include:

  • .mat: ITK/ANTs affine transform (4x4 matrix)

  • .h5: HDF5 composite transform (may contain affine and/or deformation components)

  • .nii, .nii.gz: Deformation field images

space_from

character string or ieegio_space object identifying the source space. If missing, will be inferred from the filename using BIDS-style from-<space> entity (e.g., "sub-01_from-T1w_to-MNI_xfm.h5" yields "T1w").

space_to

character string or ieegio_space object identifying the target space. If missing, will be inferred from the filename using BIDS-style to-<space> entity.

interpretation

character string specifying how to interpret the transform:

  • "passive" (default): Axis/coordinate frame transform. Represents how coordinate systems relate to each other. This is the typical interpretation for brain imaging registration transforms.

  • "active": Point transform. Directly transforms point coordinates from source to target space.

Value

An ieegio_transforms object with:

data

List containing the transform data (matrix for affine, ANTsTransform object for deformation)

type

"affine" or "deformation"

interpretation

"active" or "passive"

space_from

Source space (with "LPS" orientation for ANTs)

space_to

Target space (with "LPS" orientation for ANTs)

dimension

Spatial dimension (typically 3)

Details

ANTs transforms operate in LPS (Left-Posterior-Superior) coordinate convention. The returned transform object automatically sets orientation to "LPS" for both source and target spaces.

For composite transforms (e.g., .h5 files containing both affine and deformation components), the function returns a single transform object. Use as_ieegio_transform with a list to combine multiple transforms.

This function requires the rpyANTs package and a configured Python environment.

BIDS Support

The function can automatically infer space names from BIDS-compliant file names:

  • from-<source>: Source space identifier

  • to-<target>: Target space identifier

Example: "sub-01_from-T1w_to-MNI152NLin2009cAsym_mode-image_xfm.h5"

See also

as_ieegio_transform for converting objects to transforms and chaining transform_orientation for orientation conversion transforms

Examples

if (FALSE) { # \dontrun{
# Read an affine transform
xfm <- io_read_ants_transform("sub-01_from-T1w_to-MNI_xfm.mat")

# Explicitly specify spaces
xfm <- io_read_ants_transform(
  "transform.h5",
  space_from = "native",
  space_to = "MNI152"
)

# Read as active (point) transform
xfm <- io_read_ants_transform(
  "transform.mat",
  interpretation = "active"
)

# Chain multiple transforms
xfm1 <- io_read_ants_transform("from-T1w_to-T2w_xfm.mat")
xfm2 <- io_read_ants_transform("from-T2w_to-MNI_xfm.h5")
combined <- as_ieegio_transform(list(xfm1, xfm2))
} # }