Internal guard for Cartesian checks

Stops with a clear error message if data is not Cartesian.

Usage

ensure_is_cartesian(data)

Arguments

data

An aniframe.

Examples

af <- example_aniframe(n_obs = 3, n_individuals = 1, n_keypoints = 1)
# Passes silently when the coordinate system matches
ensure_is_cartesian(af)