in fact testing it out briefly, moving the default interpolant to `Nearest` (which I think is the correct corresponding choice) caused only one of the unit tests to fail, this one:
```
======================================================================
FAIL: Test that noise generated by a rotated CorrelatedNoise matches the parent correlated noise.
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Library/Frameworks/EPD64.framework/Versions/7.3/lib/python2.7/site-packages/nose-1.3.0-py2.7.egg/nose/case.py", line 197, in runTest
    self.test(*self.arg)
  File "/Users/browe/great3/GalSim/tests/test_correlatednoise.py", line 530, in test_output_generation_rotated
    err_msg="Generated noise field (rotated) does not match input correlation properties.")
  File "/Library/Frameworks/EPD64.framework/Versions/7.3/lib/python2.7/site-packages/numpy/testing/utils.py", line 800, in assert_array_almost_equal
    header=('Arrays are not almost equal to %d decimals' % decimal))
  File "/Library/Frameworks/EPD64.framework/Versions/7.3/lib/python2.7/site-packages/numpy/testing/utils.py", line 636, in assert_array_compare
    raise AssertionError(msg)
AssertionError: 
Arrays are not almost equal to 2 decimals
Generated noise field (rotated) does not match input correlation properties.
(mismatch 8.203125%)
 x: array([[ -4.02566114e-04,   8.03874644e-03,  -4.77557359e-04,
         -8.79812003e-04,  -1.62873259e-03,  -1.14980770e-02,
         -1.99047521e-03,  -6.90894413e-03,  -2.40374689e-03,...
 y: array([[  1.15746013e-03,   7.21110998e-03,  -7.09020140e-04,
         -7.52426227e-03,   1.31658122e-03,  -3.26225174e-03,
         -3.26225174e-03,  -1.85507414e-03,   1.78489648e-04,...

----------------------------------------------------------------------
Ran 189 tests in 18.394s

FAILED (failures=1)
Nosetests returned error code  1

Starting cpp tests...
Running 12 test cases...

*** No errors detected
test_main finished successfully.

scons: done building targets.
```
the reference and comparison images from this test do look quite badly different, however.  here is the reference rotated CF drawn out:
![ref](https://f.cloud.github.com/assets/1454961/944879/db62647e-02e3-11e3-946f-266fc58e4653.png)
and there is the CF estimated from lots of fields generated using the rotated CF:
![test](https://f.cloud.github.com/assets/1454961/944880/def04ba6-02e3-11e3-90d5-ec82bcfc586e.png)

it seems to me almost as if in the first case the nearest interpolant is not being properly rotated, but this might just be an illusion...  Mike, do you think the `Nearest` is in fact the correct interpolant to use, or am I barking up the wrong tree here?