Merge pull request #561 from ComputationalCryoEM/polar_2d_560

`PolarBasis2D` bug.

Author: j-c-c

src/aspire/basis/polar_2d.py

@@ -21,22 +21,16 @@ def __init__(self, size, nrad=None, ntheta=None, dtype=np.float32):
 
         :param size: The shape of the vectors for which to define the grid.
             Currently only square images are supported.
-        :param nrad: The number of points in the radial dimension.
-        :param ntheta: The number of points in the angular dimension.
+        :param nrad: The number of points in the radial dimension. Default is resoltuion // 2.
+        :param ntheta: The number of points in the angular dimension. Default is 8 * nrad.
         """
 
         ndim = len(size)
         ensure(ndim == 2, "Only two-dimensional grids are supported.")
         ensure(len(set(size)) == 1, "Only square domains are supported.")
 
         self.nrad = nrad
-        if nrad is None:
-            self.nrad = self.nres // 2
-
         self.ntheta = ntheta
-        if ntheta is None:
-            # try to use the same number as Fast FB basis
-            self.ntheta = 8 * self.nrad
 
         super().__init__(size, dtype=dtype)
 
@@ -46,6 +40,13 @@ def _build(self):
         """
         logger.info("Represent 2D image in a polar Fourier grid")
 
+        if self.nrad is None:
+            self.nrad = self.nres // 2
+
+        if self.ntheta is None:
+            # try to use the same number as Fast FB basis
+            self.ntheta = 8 * self.nrad
+
         self.count = self.nrad * self.ntheta
         self._sz_prod = self.sz[0] * self.sz[1]