# ModelInstance¶

class menpofit.modelinstance.ModelInstance(model)[source]

Bases: Targetable, Vectorizable, DP

Base class for creating a model that can produce a target menpo.shape.PointCloud and knows how to compute its own derivative with respect to its parametrisation.

Parameters

model (class) – The trained model (e.g. menpo.model.PCAModel).

as_vector(**kwargs)

Returns a flattened representation of the object as a single vector.

Returns

vector ((N,) ndarray) – The core representation of the object, flattened into a single vector. Note that this is always a view back on to the original object, but is not writable.

copy()

Generate an efficient copy of this object.

Note that Numpy arrays and other Copyable objects on self will be deeply copied. Dictionaries and sets will be shallow copied, and everything else will be assigned (no copy will be made).

Classes that store state other than numpy arrays and immutable types should overwrite this method to ensure all state is copied.

Returns

type(self) – A copy of this object

abstract d_dp(points)

The derivative of this spatial object with respect to the parametrisation changes evaluated at points.

Parameters

points ((n_points, n_dims) ndarray) – The spatial points at which the derivative should be evaluated.

Returns

d_dp ((n_points, n_parameters, n_dims) ndarray) – The Jacobian with respect to the parametrisation.

d_dp[i, j, k] is the scalar differential change that the k’th dimension of the i’th point experiences due to a first order change in the j’th scalar in the parametrisation vector.

from_vector(vector)

Build a new instance of the object from it’s vectorized state.

self is used to fill out the missing state required to rebuild a full object from it’s standardized flattened state. This is the default implementation, which is which is a deepcopy of the object followed by a call to from_vector_inplace(). This method can be overridden for a performance benefit if desired.

Parameters

vector ((n_parameters,) ndarray) – Flattened representation of the object.

Returns

object (type(self)) – An new instance of this class.

from_vector_inplace(vector)

Deprecated. Use the non-mutating API, from_vector.

For internal usage in performance-sensitive spots, see _from_vector_inplace()

Parameters

vector ((n_parameters,) ndarray) – Flattened representation of this object

has_nan_values()

Tests if the vectorized form of the object contains nan values or not. This is particularly useful for objects with unknown values that have been mapped to nan values.

Returns

has_nan_values (bool) – If the vectorized object contains nan values.

set_target(new_target)

Update this object so that it attempts to recreate the new_target.

Parameters

new_target (PointCloud) – The new target that this object should try and regenerate.

property n_dims

The number of dimensions of the target.

Type

int

property n_parameters

The length of the vector that this object produces.

Type

int

property n_points

The number of points on the target.

Type

int

property n_weights

The number of parameters in the linear model.

Type

int

property target

The current menpo.shape.PointCloud that this object produces.

Type

menpo.shape.PointCloud

property weights

The weights of the model.

Type

(n_weights,) ndarray