Core Concepts

The BVH format

A BVH file has two sections:

• HIERARCHY — defines a skeleton as a tree of joints. Each joint has an offset (bone vector from parent) and rotation channels (e.g., Zrotation Yrotation Xrotation). Leaf nodes called "End Sites" have only an offset.
• MOTION — per-frame data. Each frame is a row of floats: root position (3 values) followed by Euler angles for every joint.

The Bvh object

Bvh is the central container. It holds:

Attribute	Shape	Description
root_pos	(F, 3)	Root translation per frame
joint_angles	(F, J, 3)	Euler angles (radians) per joint per frame
nodes	list	All skeleton nodes (joints + end sites) in depth-first order
joint_names	list of str	Non-end-site joint names
euler_orders	list of str	Per-joint Euler orders (e.g. ['ZYX', ...])
edges	list of tuples	Skeleton edge list as (child_idx, parent_idx)
frame_time	float	Seconds per frame
world_up	str	Gravity axis (e.g. '+y', '+z'). Auto-detected, settable.

Index spaces

pybvh has two index spaces:

• node_index — includes end sites. Maps to bvh.nodes list. Used by node_positions().
• joint_angles index — excludes end sites. Maps to bvh.joint_names and bvh.joint_angles axis 1. Used by edges, euler_orders, augmentation functions.

Most functions use the joint_angles index space. The docstring of each function specifies which space it expects.

Centered modes

Several functions accept a centered parameter:

• "world" — positions as stored in the BVH file
• "skeleton" — root forced to (0, 0, 0) every frame
• "first" — first frame's root at origin, subsequent frames relative