Upload New File

brick_utils.py

+import numpy as np
+import healpy as hp
+
+
+
+def angular_distance(ra1, dec1, ra2, dec2):
+    """
+    Calculate the angular distance between two points on a sphere.
+
+    Parameters
+    ----------
+    ra1 : float
+        Right Ascension of the first point (radians).
+    dec1 : float
+        Declination of the first point (radians).
+    ra2 : float
+        Right Ascension of the second point (radians).
+    dec2 : float
+        Declination of the second point (radians).
+
+    Returns
+    -------
+    float
+        Angular distance between the two points (radians).
+    """
+    return np.arccos(
+        np.sin(dec1) * np.sin(dec2) +
+        np.cos(dec1) * np.cos(dec2) * np.cos(ra1 - ra2)
+    )
+
+def radius_exact(nside, pix_id):
+    """
+    Compute the exact minimum enclosing circle radius of a HEALPix pixel.
+
+    Parameters
+    ----------
+    nside : int
+        HEALPix resolution parameter.
+    pix_id : int
+        HEALPix pixel ID.
+
+    Returns
+    -------
+    float
+        Exact minimum enclosing circle radius of the pixel (degrees).
+    """
+    theta_c, phi_c = hp.pix2ang(nside, pix_id)
+    verts = hp.boundaries(nside, pix_id, step=1)
+    ra_v = np.arctan2(verts[1], verts[0])
+    dec_v = np.arcsin(verts[2])
+    rads = [angular_distance(phi_c, np.pi/2 - theta_c, rv, dv)
+            for rv, dv in zip(ra_v, dec_v)]
+    return np.degrees(max(rads))
\ No newline at end of file