HEALPix Nodes

This method allows us to define nodes based on the Hierarchical Equal Area isoLatitude Pixelation of a sphere (HEALPix). The resolution of the HEALPix grid is defined by the resolution parameter, which corresponds to the number of refinements of the sphere.

nodes:
  data:  # name of the nodes
    node_builder:
      _target_: anemoi.graphs.nodes.HEALPixNodes
      resolution: 3
    attributes: ...

For reference, the following table shows the number of nodes and resolution for each resolution:

HEALPix refinements specifications

Refinement level	Number of nodes	Resolution (km)	Resolution (degrees)
0	12	6371	57.296
1	48	3185.5	28.648
2	192	1592.75	14.324
3	768	796.375	7.162
4	3072	398.187	3.581
5	12288	199.094	1.790
6	49152	99.547	0.895
7	196608	49.773	0.448
8	786432	24.887	0.224
9	3145728	12.443	0.112

Warning

This class will require the healpy package to be installed. You can install it with pip install healpy.