Transform coordinates to egocentric reference frame

Transforms Cartesian coordinates into an egocentric reference frame through a two-step process: translation followed by rotation. First translates all coordinates relative to a reference keypoint, then rotates the coordinate system based on specified alignment points.

Usage

transform_to_egocentric(
  data,
  to_keypoint,
  alignment_points,
  align_perpendicular = FALSE
)

Arguments

data

movement data frame with columns: time, individual, keypoint, x, y

to_keypoint

character; keypoint to use as the new origin

alignment_points

character vector of length 2 specifying the keypoint names to use for alignment

align_perpendicular

logical; if TRUE, alignment_points will be rotated to be perpendicular to the 0-degree axis. If FALSE (default), alignment_points will be rotated to align with the 0-degree axis

Value

movement data frame in egocentric reference frame

Details

This function combines translation and rotation to create an egocentric reference frame. It:

1. Translates all coordinates relative to the specified keypoint (to_keypoint)

2. Rotates the coordinate system based on the alignment points

The translation makes the reference keypoint the new origin (0,0), while the rotation standardizes the orientation. This is particularly useful for:

• Creating egocentric reference frames

• Standardizing pose data across frames or individuals

• Analyzing relative motion patterns

Examples

if (FALSE) { # \dontrun{
# Transform coordinates to make nose the origin and align body axis
transformed_data <- transform_to_egocentric(
  data,
  to_keypoint = "nose",
  alignment_points = c("nose", "tail"),
  align_perpendicular = FALSE
)

# Transform to make nose origin and ears perpendicular to forward axis
transformed_data <- transform_to_egocentric(
  data,
  to_keypoint = "nose",
  alignment_points = c("ear_left", "ear_right"),
  align_perpendicular = TRUE
)
} # }