SKEL

SKEL is a body model with anatomical articulation, available in male and female variants.

Setup

SKEL requires registration at skel.is.tue.mpg.de.

body-models download skel

Or configure files by gender:

body-models set skel-male /path/to/skel_male.pkl
body-models set skel-female /path/to/skel_female.pkl

API

body_models.skel.numpy.SKEL

SKEL(*, model_path=None, gender='male', simplify=1.0)

Bases: body_models.skel._model.SKEL

Skinned body model with anatomical articulation.

METHOD	DESCRIPTION
apply_pose_correctives	Apply prepared pose correctives to identity-dependent rest vertices.
forward_points	Compute positions defined by a prepared vertex mapping.
forward_skeleton	Compute posed SKEL joint transforms.
forward_vertices	Compute posed SKEL vertices.
get_rest_pose	Construct canonical parameter defaults from :attr:parameter_spec.
joint_index	Resolve a common joint to this model's native joint index.
prepare_point_regressor	Preproject a vertex mapping for repeated point forwards.
forward_links	Alias the SKEL joint transforms as anatomical link transforms.
get_apose	Return the SKEL A-pose.
get_tpose	Return the SKEL T-pose.
prepare_identity	Precompute shape-dependent state for repeated forward passes.
prepare_pose	Precompute pose-dependent state for repeated forward passes.

ATTRIBUTE	DESCRIPTION
common_joints	Common anatomical joints mapped to this model's native joint names.
has_face	bool(x) -> bool
has_hands	bool(x) -> bool
num_joints	Number of joints in the skeleton.
pose_joint_indices	Canonical joints whose local transforms are driven by each pose parameter.
runtime	Array runtime used by this model.
skinning_spec	Static topology, render-rig weights, and optional pose correctives.
symmetric_joints	Left/right joint pairs as (left_index, right_index), in joint order.
NUM_BODY_POSE_COEFFS	int([x]) -> integer
NUM_HEAD_POSE_COEFFS	int([x]) -> integer
NUM_JOINTS	int([x]) -> integer
NUM_POSE_COEFFS	int([x]) -> integer
NUM_SHAPE_COEFFS	int([x]) -> integer

common_joints property

common_joints

Common anatomical joints mapped to this model's native joint names.

has_face class-attribute

has_face = False

bool(x) -> bool

Returns True when the argument x is true, False otherwise. The builtins True and False are the only two instances of the class bool. The class bool is a subclass of the class int, and cannot be subclassed.

has_hands class-attribute

has_hands = False

bool(x) -> bool

Returns True when the argument x is true, False otherwise. The builtins True and False are the only two instances of the class bool. The class bool is a subclass of the class int, and cannot be subclassed.

num_joints property

num_joints

Number of joints in the skeleton.

pose_joint_indices property

pose_joint_indices

Canonical joints whose local transforms are driven by each pose parameter.

runtime property

runtime

Array runtime used by this model.

skinning_spec property

skinning_spec

Static topology, render-rig weights, and optional pose correctives.

symmetric_joints property

symmetric_joints

Left/right joint pairs as (left_index, right_index), in joint order.

Indices address the J axis of :meth:forward_skeleton outputs and cover the whole native skeleton, including joints outside the :class:Joint vocabulary. Unpaired joints lie on the midline. Pairs describe index correspondence only, not how to mirror a pose.

RAISES	DESCRIPTION
ValueError	If a sided joint name has no counterpart.

NUM_BODY_POSE_COEFFS class-attribute

NUM_BODY_POSE_COEFFS = 43

int([x]) -> integer int(x, base=10) -> integer

Convert a number or string to an integer, or return 0 if no arguments are given. If x is a number, return x.int(). For floating point numbers, this truncates towards zero.

If x is not a number or if base is given, then x must be a string, bytes, or bytearray instance representing an integer literal in the given base. The literal can be preceded by '+' or '-' and be surrounded by whitespace. The base defaults to 10. Valid bases are 0 and 2-36. Base 0 means to interpret the base from the string as an integer literal.

int('0b100', base=0) 4

NUM_HEAD_POSE_COEFFS class-attribute

NUM_HEAD_POSE_COEFFS = 3

int([x]) -> integer int(x, base=10) -> integer

Convert a number or string to an integer, or return 0 if no arguments are given. If x is a number, return x.int(). For floating point numbers, this truncates towards zero.

If x is not a number or if base is given, then x must be a string, bytes, or bytearray instance representing an integer literal in the given base. The literal can be preceded by '+' or '-' and be surrounded by whitespace. The base defaults to 10. Valid bases are 0 and 2-36. Base 0 means to interpret the base from the string as an integer literal.

int('0b100', base=0) 4

NUM_JOINTS class-attribute

NUM_JOINTS = 24

int([x]) -> integer int(x, base=10) -> integer

Convert a number or string to an integer, or return 0 if no arguments are given. If x is a number, return x.int(). For floating point numbers, this truncates towards zero.

If x is not a number or if base is given, then x must be a string, bytes, or bytearray instance representing an integer literal in the given base. The literal can be preceded by '+' or '-' and be surrounded by whitespace. The base defaults to 10. Valid bases are 0 and 2-36. Base 0 means to interpret the base from the string as an integer literal.

int('0b100', base=0) 4

NUM_POSE_COEFFS class-attribute

NUM_POSE_COEFFS = 46

int([x]) -> integer int(x, base=10) -> integer

Convert a number or string to an integer, or return 0 if no arguments are given. If x is a number, return x.int(). For floating point numbers, this truncates towards zero.

If x is not a number or if base is given, then x must be a string, bytes, or bytearray instance representing an integer literal in the given base. The literal can be preceded by '+' or '-' and be surrounded by whitespace. The base defaults to 10. Valid bases are 0 and 2-36. Base 0 means to interpret the base from the string as an integer literal.

int('0b100', base=0) 4

NUM_SHAPE_COEFFS class-attribute

NUM_SHAPE_COEFFS = 10

int([x]) -> integer int(x, base=10) -> integer

Convert a number or string to an integer, or return 0 if no arguments are given. If x is a number, return x.int(). For floating point numbers, this truncates towards zero.

If x is not a number or if base is given, then x must be a string, bytes, or bytearray instance representing an integer literal in the given base. The literal can be preceded by '+' or '-' and be surrounded by whitespace. The base defaults to 10. Valid bases are 0 and 2-36. Base 0 means to interpret the base from the string as an integer literal.

int('0b100', base=0) 4

apply_pose_correctives

apply_pose_correctives(*, identity, pose)

Apply prepared pose correctives to identity-dependent rest vertices.

Source code in src/body_models/_base.py

def apply_pose_correctives(
    self,
    *,
    identity: SkinningIdentity,
    pose: SkinningPose,
) -> Float[Array, "*batch V 3"]:
    """Apply prepared pose correctives to identity-dependent rest vertices."""
    vertices = identity["rest_vertices"]
    coefficients = pose.get("pose_coefficients")
    if coefficients is None:
        return vertices
    basis = self._corrective_basis
    if basis is None:
        raise RuntimeError("Prepared pose has corrective coefficients, but the model has no corrective basis.")
    return vertices + basis.apply(coefficients)

forward_points

forward_points(
    body_pose,
    head_pose,
    *,
    point_regressor,
    shape=None,
    identity=None,
    global_rotation=None,
    global_translation=None,
)

Compute positions defined by a prepared vertex mapping.

Source code in src/body_models/skel/_model.py

def forward_points(
    self,
    body_pose: Float[Array, "*batch 43"],
    head_pose: Float[Array, "*batch 3"],
    *,
    point_regressor: PointRegressor,
    shape: Float[Array, "*batch 10"] | None = None,
    identity: SkelIdentity | None = None,
    global_rotation: Float[Array, "*batch 3"] | None = None,
    global_translation: Float[Array, "*batch 3"] | None = None,
) -> Float[Array, "*batch K 3"]:
    """Compute positions defined by a prepared vertex mapping."""
    self._validate_identity_arguments(identity, shape=shape)
    if identity is None:
        identity = self.prepare_identity(*self._resolve_identity_coefficients(body_pose.shape[:-1], shape=shape))

    pose = self.prepare_pose(body_pose, head_pose, identity=identity)
    return self._deform_points(point_regressor, identity, pose, global_rotation, global_translation)

forward_skeleton

forward_skeleton(
    body_pose,
    head_pose,
    *,
    shape=None,
    identity=None,
    global_rotation=None,
    global_translation=None,
    joint_indices=None,
)

Compute posed SKEL joint transforms.

Source code in src/body_models/skel/_model.py

def forward_skeleton(
    self,
    body_pose: Float[Array, "*batch 43"],
    head_pose: Float[Array, "*batch 3"],
    *,
    shape: Float[Array, "*batch 10"] | None = None,
    identity: SkelIdentity | None = None,
    global_rotation: Float[Array, "*batch 3"] | None = None,
    global_translation: Float[Array, "*batch 3"] | None = None,
    joint_indices: Sequence[int] | None = None,
) -> Float[Array, "*batch 24 4 4"]:
    """Compute posed SKEL joint transforms."""
    xp = self._runtime.xp
    self._validate_identity_arguments(identity, shape=shape)
    if identity is None:
        resolved = self._resolve_identity_coefficients(body_pose.shape[:-1], shape=shape)
        skeleton_identity = self._prepare_skeleton_identity(*resolved)
    else:
        skeleton_identity = identity

    packed_pose = pose_utils.pack_pose(xp, body_pose, head_pose)
    skeleton = core.prepare_skeleton(
        runtime=self._runtime,
        all_axes=self._assets.all_axes,
        rotation_indices=self._assets.rotation_indices,
        apose_R=self._assets.apose_R,
        apose_t=self._assets.apose_t,
        per_joint_rot=self._assets.per_joint_rot,
        child=self._assets.child,
        fixed_orientation_joints=self._assets.fixed_orientation_joints,
        scapula_r_axes=self._assets.scapula_r_axes,
        scapula_l_axes=self._assets.scapula_l_axes,
        spine_axes=self._assets.spine_axes,
        tree=self._assets.kinematic_tree,
        pose=packed_pose,
        local_joint_offsets=skeleton_identity["local_joint_offsets"],
        rest_joints=skeleton_identity["rest_joints"],
        joint_indices=joint_indices,
    )
    return skinning.transform_skeleton(
        skeleton,
        global_rotation,
        global_translation,
        xp=xp,
    )

forward_vertices

forward_vertices(
    body_pose,
    head_pose,
    *,
    shape=None,
    identity=None,
    global_rotation=None,
    global_translation=None,
    vertex_indices=None,
)

Compute posed SKEL vertices.

Source code in src/body_models/skel/_model.py

def forward_vertices(
    self,
    body_pose: Float[Array, "*batch 43"],
    head_pose: Float[Array, "*batch 3"],
    *,
    shape: Float[Array, "*batch 10"] | None = None,
    identity: SkelIdentity | None = None,
    global_rotation: Float[Array, "*batch 3"] | None = None,
    global_translation: Float[Array, "*batch 3"] | None = None,
    vertex_indices: Sequence[int] | None = None,
) -> Float[Array, "*batch V 3"]:
    """Compute posed SKEL vertices."""
    xp = self._runtime.xp
    self._validate_identity_arguments(identity, shape=shape)
    if identity is None:
        identity = self.prepare_identity(*self._resolve_identity_coefficients(body_pose.shape[:-1], shape=shape))

    pose = self.prepare_pose(body_pose, head_pose, identity=identity)
    vertices = self._runtime._skin_vertices(
        self.apply_pose_correctives(identity=identity, pose=pose),
        pose["skinning_transforms"],
        skinning=self._assets.compact_skinning,
        vertex_indices=vertex_indices,
    )
    return skinning.apply_global_transform(
        vertices,
        global_rotation,
        global_translation,
        xp=xp,
    )

get_rest_pose

get_rest_pose(*, batch_dims=(), dtype=None)

Construct canonical parameter defaults from :attr:parameter_spec.

PARAMETER	DESCRIPTION
batch_dims	Leading batch dimensions. TYPE: tuple[int, ...] DEFAULT: ()
dtype	Optional floating-point dtype. TYPE: Any | None DEFAULT: None

RETURNS	DESCRIPTION
dict[str, Float[Any, ...]]	Complete model parameters at rest.

Source code in src/body_models/_base.py

def get_rest_pose(
    self,
    *,
    batch_dims: tuple[int, ...] = (),
    dtype: Any | None = None,
) -> dict[str, Float[Array, "..."]]:
    """
    Construct canonical parameter defaults from :attr:`parameter_spec`.

    Args:
        batch_dims: Leading batch dimensions.
        dtype: Optional floating-point dtype.

    Returns:
        Complete model parameters at rest.
    """
    return {name: self._parameter_default(spec, batch_dims, dtype) for name, spec in self.parameter_spec.items()}

joint_index

joint_index(joint)

Resolve a common joint to this model's native joint index.

Source code in src/body_models/_base.py

def joint_index(self, joint: Joint) -> int:
    """Resolve a common joint to this model's native joint index."""
    if not isinstance(joint, Joint):
        raise TypeError("joint_index() expects a body_models.Joint; use joint_names.index(...) for native names.")
    try:
        native_name = self.common_joints[joint]
    except KeyError as exc:
        raise KeyError(f"{self.__class__.__name__} has no common joint {joint.value!r}") from exc
    return self.joint_names.index(native_name)

prepare_point_regressor

prepare_point_regressor(mapping)

Preproject a vertex mapping for repeated point forwards.

For Torch, call this after moving the model to its target device.

Source code in src/body_models/_base.py

def prepare_point_regressor(
    self,
    mapping: Float[Array, "K V"],
) -> PointRegressor:
    """Preproject a vertex mapping for repeated point forwards.

    For Torch, call this after moving the model to its target device.
    """
    if mapping.ndim != 2 or mapping.shape[0] < 1 or mapping.shape[1] != self.num_vertices:
        raise ValueError(
            f"mapping must have shape [K, {self.num_vertices}] with K >= 1, got {tuple(mapping.shape)}"
        )
    mapping = self._runtime.asarray(mapping, like=self.rest_vertices)
    return point_regression.prepare_point_regressor(
        mapping,
        self._skinning_weights,
        self._corrective_basis,
        runtime=self._runtime,
    )

forward_links

forward_links(
    body_pose,
    head_pose,
    *,
    shape=None,
    identity=None,
    global_rotation=None,
    global_translation=None,
)

Alias the SKEL joint transforms as anatomical link transforms.

Source code in src/body_models/skel/_model.py

def forward_links(
    self,
    body_pose: Float[Array, "*batch 43"],
    head_pose: Float[Array, "*batch 3"],
    *,
    shape: Float[Array, "*batch 10"] | None = None,
    identity: SkelIdentity | None = None,
    global_rotation: Float[Array, "*batch 3"] | None = None,
    global_translation: Float[Array, "*batch 3"] | None = None,
) -> Float[Array, "*batch 24 4 4"]:
    """Alias the SKEL joint transforms as anatomical link transforms."""
    return self.forward_skeleton(
        body_pose,
        head_pose,
        global_rotation=global_rotation,
        global_translation=global_translation,
        shape=shape,
        identity=identity,
    )

get_apose

get_apose(*, batch_dims=(), dtype=None)

Return the SKEL A-pose.

Source code in src/body_models/skel/_model.py

def get_apose(
    self,
    *,
    batch_dims: tuple[int, ...] = (),
    dtype: Any | None = None,
) -> dict[str, Float[Array, "..."]]:
    """Return the SKEL A-pose."""
    params = self.get_rest_pose(batch_dims=batch_dims, dtype=dtype)
    pose = self._runtime.asarray(SKEL_BODY_PRESETS["a_pose"], like=params["body_pose"])
    pose = self._runtime.xp.broadcast_to(pose, (*batch_dims, *pose.shape))
    params["body_pose"], params["head_pose"] = pose_utils.unpack_pose(self._runtime.xp, pose)
    return params

get_tpose

get_tpose(*, batch_dims=(), dtype=None)

Return the SKEL T-pose.

Source code in src/body_models/skel/_model.py

def get_tpose(
    self,
    *,
    batch_dims: tuple[int, ...] = (),
    dtype: Any | None = None,
) -> dict[str, Float[Array, "..."]]:
    """Return the SKEL T-pose."""
    return self.get_rest_pose(batch_dims=batch_dims, dtype=dtype)

prepare_identity

prepare_identity(shape)

Precompute shape-dependent state for repeated forward passes.

Source code in src/body_models/skel/_model.py

def prepare_identity(
    self,
    shape: Float[Array, "*batch 10"],
) -> SkelIdentity:
    """Precompute shape-dependent state for repeated forward passes."""
    return core.prepare_identity(
        self._assets.v_template,
        self._assets.shapedirs,
        self._assets.j_template,
        self._assets.j_shapedirs,
        self._assets.parent,
        shape,
        xp=self._runtime.xp,
    )

prepare_pose

prepare_pose(body_pose, head_pose, *, identity)

Precompute pose-dependent state for repeated forward passes.

Source code in src/body_models/skel/_model.py

def prepare_pose(
    self,
    body_pose: Float[Array, "*batch 43"],
    head_pose: Float[Array, "*batch 3"],
    *,
    identity: SkelIdentity,
) -> SkinningPose:
    """Precompute pose-dependent state for repeated forward passes."""
    packed_pose = pose_utils.pack_pose(self._runtime.xp, body_pose, head_pose)
    return core.prepare_pose(
        runtime=self._runtime,
        all_axes=self._assets.all_axes,
        rotation_indices=self._assets.rotation_indices,
        apose_R=self._assets.apose_R,
        apose_t=self._assets.apose_t,
        per_joint_rot=self._assets.per_joint_rot,
        child=self._assets.child,
        fixed_orientation_joints=self._assets.fixed_orientation_joints,
        scapula_r_axes=self._assets.scapula_r_axes,
        scapula_l_axes=self._assets.scapula_l_axes,
        spine_axes=self._assets.spine_axes,
        tree=self._assets.kinematic_tree,
        num_joints_smpl=self._assets.num_joints_smpl,
        pose=packed_pose,
        local_joint_offsets=identity["local_joint_offsets"],
        rest_joints=identity["rest_joints"],
    )