Cover requests

This tutorial explains how to find all the HEALPix cells which intersect a geographic region.

Type of requests

1. Cone Coverage

Find all cells within a given radius around a point.

import numpy as np
from healpix_geo.nested import cone_coverage

# Center and radius
lon_center = 2.3522  # Paris
lat_center = 48.8566
radius_deg = 1.0  # radius in degrees (~111 km)
depth = 8

cells = cone_coverage((lon_center, lat_center), radius_deg, depth, ellipsoid="WGS84")

print(f"Number of cells in the radius: {len(cells)}")

Number of cells in the radius: 3

2. Box Coverage

Find all cells in a spherical rectangle.

from healpix_geo.nested import box_coverage

# Coverage box
lon_min, lat_min = 2.0, 48.5
lon_max, lat_max = 3.0, 49.0

center = (
    0.5 * (lon_min + lon_max),
    0.5 * (lat_min + lat_max),
)

size = (
    lon_max - lon_min,
    lat_max - lat_min,
)

angle = 0.0
depth = 8

cells = box_coverage(center, size, angle, depth, ellipsoid="WGS84", flat=True)

print(f"Cells number : {len(cells)}")

Cells number : 3

3. Polygon coverage

Find all cells in a polygon coverage.

from healpix_geo.nested import polygon_coverage
import numpy as np

vertices = np.array([[2.0, 48.5], [3.0, 48.5], [2.5, 49.0]])

depth = 8

cells = polygon_coverage(vertices, depth, ellipsoid="WGS84", flat=True)

print(f"Cells in the polygon : {len(cells)}")

Cells in the polygon : 3

Summary

Principal functions working on geometries

Function	Usage	Key parameters
zone_coverage	Zone request	bbox, depth
cone_coverage	Circular request	center, radius, depth
box_coverage	Rectangular request	center, size, angle, depth
elliptical_cone_coverage	Elliptical cone request	center, ellipse_geometry, position_angle, depth
polygon_coverage	Polygonal request	vertices, depth

Principal functions working on a region represented by cells

Function	Usage	Key parameters
internal_boundary	Boundaries	depth, ipix

Next Steps

Working MOC

Work with MOC

Performance

Performance optimisations

Hierarchy

Hierarchical Indexing

Api reference

API reference