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mindspore.nn.MeanSurfaceDistance

class mindspore.nn.MeanSurfaceDistance(symmetric=False, distance_metric='euclidean')

Computes the Average Surface Distance from y_pred to y under the default setting. It measures how much, on average, the surface varies between the segmentation and the GT (ground truth).

Given two sets A and B, S(A) denotes the set of surface voxels of A. The shortest distance of an arbitrary voxel v to S(A) is defined as:

$$\text{dis}(v,S(A))=\underset{s_A\in S(A)}{\text{min }}\Vert v-s_A\Vert$$

The Average Surface Distance from set(B) to set(A) is given by:

$$AvgSurDis(B\to A)=\frac{\sum _{s_B\in S(B)}^{}\text{dis}(s_B,S(A))}{|S(B)|}$$

Where the ||*|| denotes a distance measure. |*| denotes the number of elements.

The mean of surface distance from set(B) to set(A) and from set(A) to set(B) is:

$$MeanSurDis(A\leftrightarrow B)=\frac{\sum _{s_A\in S(A)}^{}\text{dis}(s_A,S(B))+\sum _{s_B\in S(B)}^{}\text{dis}(s_B,S(A))}{|S(A)|+|S(B)|}$$

Parameters

• distance_metric (string) – Three measurement methods are supported: “euclidean”, “chessboard” or “taxicab”. Default: “euclidean”.

• symmetric (bool) – Whether to calculate the Mean Surface Distance between y_pred and y. If False, it only calculates $AvgSurDis(y_{p}red\to y)$, otherwise, the mean of distance from y_pred to y and from y to y_pred, i.e. $MeanSurDis(y_{pred}\leftrightarrow y)$, will be returned. Default: False.

Supported Platforms:

Ascend GPU CPU

Examples

>>> import numpy as np
>>> from mindspore import nn, Tensor
>>> x = Tensor(np.array([[3, 0, 1], [1, 3, 0], [1, 0, 2]]))
>>> y = Tensor(np.array([[0, 2, 1], [1, 2, 1], [0, 0, 1]]))
>>> metric = nn.MeanSurfaceDistance(symmetric=False, distance_metric="euclidean")
>>> metric.clear()
>>> metric.update(x, y, 0)
>>> mean_average_distance = metric.eval()
>>> print(mean_average_distance)
0.8047378541243649

clear()

Clears the internal evaluation result.

eval()

Calculate mean surface distance.

Returns

numpy.float64. The mean surface distance value.

Raises

RuntimeError – If the update method is not called first, an error will be reported.

update(*inputs)

Updates the internal evaluation result ‘y_pred’, ‘y’ and ‘label_idx’.

Parameters

inputs – Input ‘y_pred’, ‘y’ and ‘label_idx’. ‘y_pred’ and ‘y’ are a Tensor, list or numpy.ndarray. ‘y_pred’ is the predicted binary image. ‘y’ is the actual binary image. ‘label_idx’, the data type of label_idx is int.

Raises

• ValueError – If the number of the inputs is not 3.

• TypeError – If the data type of label_idx is not int or float.

• ValueError – If the value of label_idx is not in y_pred or y.

• ValueError – If y_pred and y have different shapes.