vol.sample.at.coords: Sample a 3D volume at world coordinates.

In fsbrain: Managing and Visualizing Brain Surface Data

Sample a 3D volume at world coordinates.

Description

This is the core of the volume-to-surface projection: the world coordinates (e.g., surface vertex positions) are transformed into voxel coordinates using the inverse of the affine matrix, and the volume is then sampled at those coordinates.

Usage

vol.sample.at.coords(
  volume_data,
  affine,
  coords,
  interpolation = "trilinear",
  clamp = FALSE,
  check_outside = TRUE
)

Arguments

volume_data	numeric 3D array, the volume data.
affine	numeric 4x4 matrix, maps 0-based voxel indices (column, row, slice) to world coordinates.
coords	numeric matrix with 3 columns and one row per query point, the world coordinates at which to sample the volume.
interpolation	character string, one of 'trilinear' (or its alias 'linear') or 'nearest'.
clamp	logical, whether to clamp query points which are outside the volume to the closest voxel at the volume border (edge replication). If FALSE, such points get the value NA.
check_outside	logical, whether to determine which of the query points are outside the volume. Setting this to FALSE saves the (small) cost of the comparison, but the caller cannot report or mask such points.

Value

named list with entries 'values' (numeric vector) and 'outside' (logical vector or NULL if check_outside is FALSE).

fsbrain documentation built on Sept. 27, 2026, 1:07 a.m.