Convert segments to joints: one angle per joint

Computes the angle of each joint of a structure from the directions of its two segments a and b, with angle_between():

• In 2D, the signed angle turning from a to b, in [-pi, pi], positive from x toward y. get_angle_direction() says how that looks on screen.

• In 3D with no joint axis, the included angle, in [0, pi].

• In 3D with an axis ("x", "y", "z" or a segment name), the signed angle about it after projecting both segments onto the plane perpendicular to it.

The angle is 0 when the two segments point the same way. The segment key is replaced by a joint key, the angle is in the frame's unit_angle, and confidence is the lower of the two segments'.

A joint frame cannot be converted back: it keeps no lengths and, in 3D, no rotation about the segments themselves.

Usage

as_anijoint(data, structure = NULL)

Arguments

data

An as_anisegment() frame, or an anipoint, which is converted to segments first.

structure

For an anipoint, the structure to use; see as_anisegment().

Value

An anijoint.

See also

angle_between(), anistructure()

Examples

af <- example_anipoint(n_obs = 3, n_individuals = 1) |>
  set_structure(example_structure())
as_anijoint(af)
#> # anijoint:  9 × 7
#> # Groups:    individual, joint, session, trial [3]
#> # Structure: keypoint
#>   individual joint      session trial  time angle confidence
#>        <int> <fct>        <int> <int> <int> <dbl>      <dbl>
#> 1          1 neck             1     1     1 -2.99      0.379
#> 2          1 neck             1     1     2  1.59      0.568
#> 3          1 neck             1     1     3  2.51      0.547
#> 4          1 knee_right       1     1     1 -1.45      0.427
#> 5          1 knee_right       1     1     2 -2.15      0.843
#> 6          1 knee_right       1     1     3  2.26      0.549
#> 7          1 knee_left        1     1     1 -2.58      0.614
#> 8          1 knee_left        1     1     2  1.10      0.783
#> 9          1 knee_left        1     1     3 -3.13      0.586