Implement c-type cells in crystallography module

src/pyFAI/crystallography/cell.py

@@ -40,7 +40,7 @@
 __contact__ = "Jerome.Kieffer@ESRF.eu"
 __license__ = "MIT"
 __copyright__ = "European Synchrotron Radiation Facility, Grenoble, France"
-__date__ = "06/10/2025"
+__date__ = "09/01/2026"
 __status__ = "production"
 
 import os
@@ -49,6 +49,7 @@
 import itertools
 from math import sin, cos, sqrt, pi, ceil
 from ..io.calibrant_config import CalibrantConfig, Miller, Reflection
+from .space_groups import ReflectionCondition
 from ..utils.decorators import deprecated
 
 logger = logging.getLogger(__name__)
@@ -74,7 +75,9 @@ class Cell:
         "P": "Primitive",
         "I": "Body centered",
         "F": "Face centered",
-        "C": "Side centered",
+        "A": "a-End centered",
+        "B": "b-End centered",
+        "C": "c-End centered",
         "R": "Rhombohedral",
     }
 
@@ -91,7 +94,7 @@ def __init__(
     ):
         """Constructor of the Cell class:
 
-        Crystalographic units are Angstrom for distances and degrees for angles !
+        Crystallographic units are Angstrom for distances and degrees for angles !
 
         :param a,b,c: unit cell length in Angstrom
         :param alpha, beta, gamma: unit cell angle in degrees
@@ -258,15 +261,9 @@ def type(self):
     @type.setter
     def type(self, lattice_type):
         self._type = lattice_type if lattice_type in self.types else "P"
-        self.selection_rules = [lambda h, k, l: not (h == 0 and k == 0 and l == 0)]  # noqa: E741
-        if self._type == "I":
-            self.selection_rules.append(lambda h, k, l: (h + k + l) % 2 == 0)  # noqa: E741
-        if self._type == "F":
-            self.selection_rules.append(
-                lambda h, k, l: (h % 2 + k % 2 + l % 2) in (0, 3)  # noqa: E741
-            )
-        if self._type == "R":
-            self.selection_rules.append(lambda h, k, l: ((h - k + l) % 3 == 0))  # noqa: E741
+        self.selection_rules = [ReflectionCondition.default]
+        if self._type != "P":
+            self.selection_rules.append(getattr(ReflectionCondition, f"type_{self._type}"))
 
     get_type = deprecated(type.fset, reason="property", replacement="type", since_version="2025.07")
     set_type = deprecated(type.fset, reason="property", replacement="type", since_version="2025.07")

src/pyFAI/crystallography/space_groups.py

@@ -41,7 +41,7 @@
 __contact__ = "Jerome.Kieffer@ESRF.eu"
 __license__ = "MIT"
 __copyright__ = "European Synchrotron Radiation Facility, Grenoble, France"
-__date__ = "08/10/2025"
+__date__ = "09/01/2026"
 __status__ = "production"
 
 
@@ -57,6 +57,57 @@ class ReflectionCondition:
     Help is welcome to polish this class and fix the non-validated ones.
     """
 
+    @staticmethod
+    def default(h: int, k: int, l: int) -> bool:  # noqa: E741
+        """
+        Default selection rule: h=k=l=0 is forbidden
+        """
+        return not (h == 0 and k == 0 and l == 0)
+
+    type_P = default
+
+    @staticmethod
+    def type_A(h: int, k: int, l: int) -> bool:  # noqa: E741
+        """
+        End-centered A type: h+l even
+        """
+        return ((h + l) % 2 == 0)
+
+    @staticmethod
+    def type_B(h: int, k: int, l: int) -> bool:  # noqa: E741
+        """
+        End-centered B type: k+l even
+        """
+        return ((k + l) % 2 == 0)
+
+    @staticmethod
+    def type_C(h: int, k: int, l: int) -> bool:  # noqa: E741
+        """
+        End-centered C type: h+k even
+        """
+        return ((h + k) % 2 == 0)
+
+    @staticmethod
+    def type_F(h: int, k: int, l: int) -> bool:  # noqa: E741
+        """
+        Face-centered type: h,k,l all even or all odd
+        """
+        return (h % 2 + k % 2 + l % 2) in (0, 3)
+
+    @staticmethod
+    def type_I(h: int, k: int, l: int) -> bool:  # noqa: E741
+        """
+        Body-centered type: h+k+l even
+        """
+        return (h + k + l) % 2 == 0
+
+    @staticmethod
+    def type_R(h: int, k: int, l: int) -> bool:  # noqa: E741
+        """
+        Rhombohedral type: h-k+l multiple of 3
+        """
+        return ((h - k + l) % 3 == 0)
+
     @staticmethod
     def group1_P1(h: int, k: int, l: int) -> bool:  # noqa: E741
         """

src/pyFAI/test/test_crystallography.py

@@ -33,13 +33,13 @@
 __contact__ = "Jerome.Kieffer@ESRF.eu"
 __license__ = "MIT"
 __copyright__ = "European Synchrotron Radiation Facility, Grenoble, France"
-__date__ = "09/07/2025"
+__date__ = "09/01/2026"
 
 import unittest
 import numpy
 import logging
 from .utilstest import UtilsTest
-from ..crystallography import resolution
+from ..crystallography import resolution, Cell, ReflectionCondition
 
 logger = logging.getLogger(__name__)
 
@@ -79,6 +79,18 @@ def test_langford(self):
         self.assertTrue(numpy.allclose(c.sigma(numpy.linspace(0.1,1,10)), ref))
         self.assertTrue(isinstance(c.fwhm(1), float))
 
+    def test_bug_2755(self):
+        "Missing default selection rule for C-type cells"
+        phase1 = Cell.monoclinic(3, 4, 5, 115, lattice_type='C')
+        res1 = len(phase1.calculate_dspacing(dmin=1))
+
+        phase2 = Cell.monoclinic(3, 4, 5, 115, lattice_type='P')
+        res0 = len(phase2.calculate_dspacing(dmin=1))
+        phase2.selection_rules.append(ReflectionCondition.group5_C2)
+        res2 = len(phase2.calculate_dspacing(dmin=1))
+        self.assertEqual(res1, res2)
+        self.assertGreater(res0, res2)
+
 
 def suite():
     testsuite = unittest.TestSuite()