Many problems across computer vision and the natural sciences require the
analysis of spherical data, for which representations may be learned
efficiently by encoding equivariance to rotational symmetries. We present a
generalized spherical CNN framework that encompasses various existing
approaches and allows them to be leveraged alongside each other. The only
existing non-linear spherical CNN layer that is strictly equivariant has
complexity $\mathcal{O}(C^2L^5)$, where $C$ is a measure of representational
capacity and $L$ the spherical harmonic bandlimit. Such a high computational
cost often prohibits the use of strictly equivariant spherical CNNs. We develop
two new strictly equivariant layers with reduced complexity $\mathcal{O}(CL^4)$
and $\mathcal{O}(CL^3 \log L)$, making larger, more expressive models
computationally feasible. Moreover, we adopt efficient sampling theory to
achieve further computational savings. We show that these developments allow
the construction of more expressive hybrid models that achieve state-of-the-art
accuracy and parameter efficiency on spherical benchmark problems.

提出了一种广义的球形卷积神经网络框架，其中包括了各种现有方法，并允许它们同时被利用。通过开发两个新的严格相等层，其复杂度已经被降至可行水平，使球形 CNNs 的更大、更具表现力模型能够被计算出来。通过这些发展，展示了对于球形基准问题，能够构建更具表现力的混合模型，达到最新的精度和参数效率。

高效广义球形卷积神经网络

Efficient Generalized Spherical CNNs

Convolutional Neural Networks (CNNs) are a cornerstone of the Deep Learning
toolbox and have led to many breakthroughs in Artificial Intelligence. These
networks have mostly been developed for regular Euclidean domains such as those
supporting images, audio, or video. Because of their success, CNN-based methods
are becoming increasingly popular in Cosmology. Cosmological data often comes
as spherical maps, which make the use of the traditional CNNs more complicated.
The commonly used pixelization scheme for spherical maps is the Hierarchical
Equal Area isoLatitude Pixelisation (HEALPix). We present a spherical CNN for
analysis of full and partial HEALPix maps, which we call DeepSphere. The
spherical CNN is constructed by representing the sphere as a graph. Graphs are
versatile data structures that can act as a discrete representation of a
continuous manifold. Using the graph-based representation, we define many of
the standard CNN operations, such as convolution and pooling. With filters
restricted to being radial, our convolutions are equivariant to rotation on the
sphere, and DeepSphere can be made invariant or equivariant to rotation. This
way, DeepSphere is a special case of a graph CNN, tailored to the HEALPix
sampling of the sphere. This approach is computationally more efficient than
using spherical harmonics to perform convolutions. We demonstrate the method on
a classification problem of weak lensing mass maps from two cosmological models
and compare the performance of the CNN with that of two baseline classifiers.
The results show that the performance of DeepSphere is always superior or equal
to both of these baselines. For high noise levels and for data covering only a
smaller fraction of the sphere, DeepSphere achieves typically 10% better
classification accuracy than those baselines. Finally, we show how learned
filters can be visualized to introspect the neural network.

本文提出了一种适用于球形映射的基于图表达的卷积神经网络 DeepSphere，该方法在宇宙学领域中有着广泛的应用，通过对弱透镜质量图的分类问题的实验结果显示，DeepSphere 在高噪声和数据覆盖只有较小部分球面的情况下，通常比其他基线分类器在分类精度上提高 10%。