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Create a structure: points, the segments between them, and joints

Source: R/anistructure.R
anistructure.Rd

[Experimental]

An anistructure describes how the levels of one identity or temporal variable relate: the keypoints of a skeleton, or the players of a team. It has three parts, each optional beyond the first:

  • points — the members, levels of the variable it is attached to.

  • segments — directed links between two points, with an optional expected length. Direction matters for joint angles: run limbs proximal to distal, and paired segments (left to right) the same way.

  • joints — one measured angle each, between an ordered pair of segments (a, b), with optional limits min, max and rest in radians. The angle is 0 when the two segments point the same way. In 2D it is signed, turning from a to b. In 3D it is the included angle, or, when axis is given ("x", "y", "z" or a segment name), the signed angle about it. Several angles on the same pair of segments — flexion and abduction, say — are several joints with different axes.

Lengths and limits are recorded, not enforced: checks compare the data against them.

A structure is a template: it records no data and no variable until it is attached to a frame with set_structure(), so one structure can be reused across frames.

Usage

anistructure(
  points = NULL,
  segments = NULL,
  joints = NULL,
  root = NA_character_,
  source = NA_character_,
  citation = NA_character_,
  license = NA_character_
)

Arguments

points

Character vector of point names. Defaults to the segment endpoints.

segments

A data frame with from and to, and optionally segment (defaults to "from-to") and length; or a list of c(from, to) pairs.

joints

A data frame with a and b (segment names), and optionally joint (defaults to "a-b"), axis, min, max and rest.

root

The point the structure hangs from when positions are rebuilt from segments. NA if unset.

source, citation, license

Provenance of the structure.

Value

An anistructure.

See also

set_structure(), example_structure()

Examples

anistructure(
  segments = data.frame(
    segment = c("thigh", "shin"),
    from = c("hip", "knee"),
    to = c("knee", "ankle")
  ),
  joints = data.frame(joint = "knee", a = "thigh", b = "shin", min = 0, max = 2.5),
  root = "hip"
)

# A team: points only, or points with links between them
anistructure(points = c("gk", "lb", "cb", "rb"))
anistructure(segments = list(c("lb", "cb"), c("cb", "rb")))