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Convert an anipoint to segments: a length and a direction per segment

Source: R/anisegment.R
as_anisegment.Rd

[Experimental]

Re-expresses the positions of a structure's points as its segments. Each row is one segment at one time: its length and the unit vector ux, uy (and uz in 3D) pointing from the segment's from point to its to point, in the frame's axes and units.

The structure's variable (usually keypoint) is replaced by a segment key. Structures over that variable other than structure are dropped; those over the remaining keys are kept. A confidence column becomes the lower of the two endpoints' values; other undeclared columns are dropped.

as_anipoint() rebuilds positions from the segments, anchored at the root point's trajectory. That is useful after editing the segments — for example holding each segment's length constant — since every point but the root then moves to agree with them.

Usage

as_anisegment(data, structure = NULL)

Arguments

data

A Cartesian 2D or 3D anipoint.

structure

Name of the structure to use. May be omitted when only one structure has segments.

Value

An anisegment.

See also

anistructure(), set_structure()

Examples

af <- example_anipoint(n_obs = 3, n_individuals = 1) |>
  set_structure(example_structure())
seg <- as_anisegment(af)
seg
#> # anisegment: 30 × 9
#> # Groups:     individual, segment, session, trial [10]
#> # Structure:  keypoint
#>    individual segment        session trial  time length     ux     uy confidence
#>         <int> <fct>            <int> <int> <int>  <dbl>  <dbl>  <dbl>      <dbl>
#>  1          1 spine                1     1     1  1.65   0.357 -0.934      0.703
#>  2          1 spine                1     1     2  2.19   0.463  0.887      0.497
#>  3          1 spine                1     1     3  2.46   0.546  0.838      0.698
#>  4          1 head                 1     1     1  1.59  -0.105  0.994      0.745
#>  5          1 head                 1     1     2  3.24  -0.642 -0.767      0.497
#>  6          1 head                 1     1     3  1.62  -0.715 -0.699      0.698
#>  7          1 shoulder_right       1     1     1  1.47   0.568  0.823      0.862
#>  8          1 shoulder_right       1     1     2  2.96  -0.476 -0.879      0.463
#>  9          1 shoulder_right       1     1     3  0.434 -0.828 -0.561      0.698
#> 10          1 shoulder_left        1     1     1  0.627  0.151  0.989      0.751
#> # ℹ 20 more rows

# Hold each segment's length constant, then rebuild the positions
rigid <- seg |>
  dplyr::mutate(length = stats::median(length))
rebuilt <- as_anipoint(rigid, root = af)