feat: add from_box to create rectangular MOCs

CHANGELOG.md

@@ -28,6 +28,7 @@ a column name to sum. It returns the sum of the column in the intersection betwe
 MOC and the Multi-order-map. `MOC.probability_in_multiordermap` has a similar
 behavior but also converts a probability-density into a probability.
 * `STMOC.new_empty()` allows to create a new empty Space-Time MOC.
+* `MOC.from_box` to create rectangular MOCs
 
 ## [0.13.1]
 

python/mocpy/moc/moc.py

@@ -1031,6 +1031,58 @@ def from_cone(cls, lon, lat, radius, max_depth, delta_depth=2):
             np.uint8(delta_depth),
         )
         return cls(index)
+
+    @classmethod
+    @validate_lonlat
+    def from_box(cls, lon, lat, a, b, angle, max_depth):
+        """
+        Create a MOC from a cone.
+
+        The cone is centered around the (`lon`, `lat`) position with a radius expressed by
+        `radius`.
+
+        Parameters
+        ----------
+        lon : `~astropy.coordinates.Longitude` or its supertype `~astropy.units.Quantity`
+            The longitude of the center of the cone.
+        lat : `~astropy.coordinates.Latitude` or its supertype `~astropy.units.Quantity`
+            The latitude of the center of the cone.
+        a : `~astropy.coordinates.Angle`
+            The semi-major axis of the box, i.e. half of the box's width.
+        b : `~astropy.coordinates.Angle`
+            The semi-minor axis of the box, i.e. half of the box's height.
+        angle : `astropy.coordinates.Angle`
+            The tilt angle between the north and the semi-major axis, east of north.
+        max_depth : int
+            Maximum HEALPix cell resolution.
+
+        Returns
+        -------
+        result : `~mocpy.moc.MOC`
+            The resulting MOC
+
+        Examples
+        --------
+        >>> from mocpy import MOC
+        >>> from astropy.coordinates import Angle, Longitude, Latitude
+        >>> moc = MOC.from_box(
+        ...  lon=Longitude("0d"),
+        ...  lat=Latitude("0d"),
+        ...  a=Angle("10d"),
+        ...  b=Angle("2d"),
+        ...  angle=Angle("30d"),
+        ...  max_depth=10
+        ... )
+        """
+        index = mocpy.from_box(
+            lon[0],
+            lat[0],
+            np.float64(a.to_value(u.deg)),
+            np.float64(b.to_value(u.deg)),
+            np.float64(angle.to_value(u.deg)),
+            np.uint8(max_depth)
+        )
+        return cls(index)
 
     @classmethod
     @validate_lonlat

python/mocpy/tests/test_moc.py

@@ -1,4 +1,5 @@
 import copy
+import math
 import re
 
 import astropy.units as u
@@ -525,6 +526,17 @@ def test_from_ring():
         max_depth=10,
     )
 
+def test_from_box():
+    a = Angle("10d")
+    b = Angle("2d")
+    moc = MOC.from_box(
+        lon=Longitude("0d"), lat=Latitude("0d"),
+        a=a, b=b, angle=Angle("30d"),max_depth=10)
+    area = moc.sky_fraction * 4 * math.pi * u.steradian
+    # the moc covers a slightly bigger area than the region defined by the
+    # parameters
+    assert area.to(u.deg**2).value > 80
+    assert area.to(u.deg**2).value < 90
 
 # TODO: IMPROVE THE ALGO
 """

src/lib.rs

@@ -158,6 +158,42 @@ fn mocpy(_py: Python, m: &PyModule) -> PyResult<()> {
       .map_err(PyValueError::new_err)
   }
 
+  /// # Input
+  /// - `lon` the longitude of the center of the box, in radians
+  /// - `lat` the latitude of the center of the box, in radians
+  /// - `a` the semi-major axis of the box (half the box width), in radians
+  /// - `b` the semi-minor axis of the box (half the box height), in radians
+  /// - `pa` the position angle (i.e. the angle between the north and the semi-major axis, east-of-north), in radians
+  /// - `depth`: the MOC depth
+  /// - `selection`: select BMOC cells to keep in the MOC
+  ///
+  /// # Panics
+  /// - if `a` not in `]0, pi/2]`
+  /// - if `b` not in `]0, a]`
+  /// - if `pa` not in `[0, pi[`
+  ///
+  #[pyfn(m)]
+  pub fn from_box(
+    lon: f64,
+    lat: f64,
+    a: f64,
+    b: f64,
+    angle: f64,
+    depth: u8,
+  ) -> PyResult<usize> {
+    U64MocStore::get_global_store()
+      .from_box(
+        lon,
+        lat,
+        a,
+        b,
+        angle,
+        depth,
+        CellSelection::All
+      )
+      .map_err(PyValueError::new_err)
+  }
+
   /// Create a spatial coverage from a given ring.
   ///
   /// # Arguments