Add utilities so that freud.diffraction.Diffractometer can be used like bitbucket diffractometer code

cmeutils/__init__.py

@@ -1,4 +1,4 @@
-from . import gsd_utils
+from . import gsd_utils, structure
 from .__version__ import __version__
 
-__all__ = ["__version__", "gsd_utils"]
+__all__ = ["__version__", "gsd_utils", "structure"]

cmeutils/structure.py

@@ -1,8 +1,33 @@
-from cmeutils import gsd_utils
 import freud
 import gsd
 import gsd.hoomd
 import numpy as np
+from rowan import vector_vector_rotation
+
+from cmeutils import gsd_utils
+
+
+def get_quaternions(n_views = 20):
+    """Get the quaternions for the specified number of views."""
+    # Calculate points for even distribution on a sphere
+    ga = np.pi * (3 - 5**0.5)
+    theta = ga * np.arange(n_views-3)
+    z = np.linspace(1 - 1/(n_views-3), 1/(n_views-3), n_views-3)
+    radius = np.sqrt(1 - z * z)
+    points = np.zeros((n_views, 3))
+    points[:-3,0] = radius * np.cos(theta)
+    points[:-3,1] = radius * np.sin(theta)
+    points[:-3,2] = z
+
+    # face on
+    points[-3] = np.array([0, 0, 1])
+    # edge on
+    points[-2] = np.array([0, 1, 1])
+    # corner on
+    points[-1] = np.array([1, 1, 1])
+
+    unit_z = np.array([0, 0, 1])
+    return [vector_vector_rotation(i, unit_z) for i in points]
 
 
 def gsd_rdf(

environment.yml

@@ -9,3 +9,4 @@ dependencies:
   - python=3.7
   - pytest
   - pytest-cov
+  - rowan