added ball method for tfields.Points3D

tfields/points3D.py

@@ -7,6 +7,7 @@ Mail:       daniel.boeckenhoff@ipp.mpg.de
 basic threedimensional tensors
 """
 import tfields
+import numpy as np
 
 
 class Points3D(tfields.Tensors):
@@ -138,6 +139,26 @@ class Points3D(tfields.Tensors):
             kwargs['dim'] = 3
         return super(Points3D, cls).__new__(cls, tensors, **kwargs)
 
+    def balls(self, radius, spacing=(5, 3)):
+        """
+        Buils a sphere around each point with resolution
+        Args:
+            radius (float): radius of spheres
+            spacing (tuple of int): n_phi, n_theta
+        """
+        sphere = tfields.Mesh3D.grid((radius, radius, 1),
+                                     (-np.pi, np.pi, spacing[0]),
+                                     (-np.pi / 2, np.pi / 2, spacing[1]),
+                                     coord_sys='spherical')
+        sphere.transform('cartesian')
+        balls = []
+        with self.tmp_transform('cartesian'):
+            for point in self:
+                ball = sphere.copy()
+                ball += point
+                balls.append(ball)
+        return tfields.Mesh3D.merged(*balls)
+
 
 if __name__ == '__main__':  # pragma: no cover
     import doctest