Error when cropping a 1D NDCube

Start by reproducing the 1D example and read NDCubeBase._get_crop_item in ndcube.py together with get_crop_item_from_points in utils/cube.py. Trace the 1D world-to-array index conversion and compare it with the working 2D example. Done means cropping the 1D NDCube with the supplied wavelength bounds returns the expected sliced cube without an exception.

Describe the bug

Attempting to crop a 1D NDcube errors.

To Reproduce

import numpy as np

import astropy.wcs
import astropy.units as u

from ndcube import NDCube

data_1d = np.arange(200)

wcs_1d = astropy.wcs.WCS(naxis=1)
wcs_1d.wcs.ctype = 'WAVE',
wcs_1d.wcs.cunit = 'nm',
wcs_1d.wcs.cdelt = 4,
wcs_1d.wcs.crpix = 1,
wcs_1d.wcs.crval = 3,

cube_1d = NDCube(data_1d, wcs=wcs_1d)
cube_1d.crop((7*u.nm,), (15*u.nm,))

gives

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[78], line 1
----> 1 cube_1d.crop((7*u.nm,), (15*u.nm,))

File ~\AppData\Local\mambaforge\envs\py312\Lib\site-packages\ndcube\ndcube.py:622, in NDCubeBase.crop(self, wcs, keepdims, *points)
    619 def crop(self, *points, wcs=None, keepdims=False):
    620     # The docstring is defined in NDCubeABC
    621     # Calculate the array slice item corresponding to bounding box and return sliced cube.
--> 622     item = self._get_crop_item(*points, wcs=wcs, keepdims=keepdims)
    623     return self[item]

File ~\AppData\Local\mambaforge\envs\py312\Lib\site-packages\ndcube\utils\cube.py:57, in sanitize_wcs.<locals>.wcs_wrapper(*args, **kwargs)
     53     raise TypeError("wcs argument must be a High Level WCS or an ExtraCoords object.")
     55 params.arguments['wcs'] = wcs
---> 57 return func(*params.args, **params.kwargs)

File ~\AppData\Local\mambaforge\envs\py312\Lib\site-packages\ndcube\ndcube.py:648, in NDCubeBase._get_crop_item(self, wcs, keepdims, *points)
    644         if not (value is None or isinstance(value, classes[j])):
    645             raise TypeError(f"{type(value)} of component {j} in point {i} is "
    646                             f"incompatible with WCS component {comp[j]} "
    647                             f"{classes[j]}.")
--> 648 return utils.cube.get_crop_item_from_points(points, wcs, False, keepdims=keepdims)

File ~\AppData\Local\mambaforge\envs\py312\Lib\site-packages\ndcube\utils\cube.py:183, in get_crop_item_from_points(points, wcs, crop_by_values, keepdims)
    181         point_array_indices = tuple(a.item() for a in point_array_indices)
    182 else:
--> 183     point_array_indices = HighLevelWCSWrapper(sliced_wcs).world_to_array_index(
    184         *sliced_point)
    185     # If returned value is a 0-d array, convert to a length-1 tuple.
    186     if isinstance(point_array_indices, np.ndarray) and point_array_indices.ndim == 0:

File ~\OneDrive - NASA\code\astropy\astropy\wcs\wcsapi\high_level_api.py:129, in BaseHighLevelWCS.world_to_array_index(self, *world_objects)
    117 """
    118 Convert world coordinates (represented by Astropy objects) to array
    119 indices.
   (...)
    126 as rounded integers.
    127 """
    128 if self.low_level_wcs.pixel_n_dim == 1:
--> 129     return _toindex(self.world_to_pixel(*world_objects))
    130 else:
    131     return tuple(_toindex(self.world_to_pixel(*world_objects)[::-1]).tolist())

File ~\OneDrive - NASA\code\astropy\astropy\wcs\wcsapi\high_level_api.py:356, in HighLevelWCSMixin.world_to_pixel(self, *world_objects)
    351 world_values = high_level_objects_to_values(
    352     *world_objects, low_level_wcs=self.low_level_wcs
    353 )
    355 # Finally we convert to pixel coordinates
--> 356 pixel_values = self.low_level_wcs.world_to_pixel_values(*world_values)
    358 return pixel_values

File ~\OneDrive - NASA\code\astropy\astropy\wcs\wcsapi\wrappers\sliced_wcs.py:271, in SlicedLowLevelWCS.world_to_pixel_values(self, *world_arrays)
    268         world_arrays_new.append(sliced_out_world_coords[iworld])
    270 world_arrays_new = np.broadcast_arrays(*world_arrays_new)
--> 271 pixel_arrays = list(self._wcs.world_to_pixel_values(*world_arrays_new))
    273 for ipixel in range(self._wcs.pixel_n_dim):
    274     if (
    275         isinstance(self._slices_pixel[ipixel], slice)
    276         and self._slices_pixel[ipixel].start is not None
    277     ):

TypeError: iteration over a 0-d array

Adding a second dimension to the NDCube "fixes" the problem:

data_2d = data_1d[np.newaxis, :]

wcs_2d = astropy.wcs.WCS(naxis=2)
wcs_2d.wcs.ctype = 'WAVE', 'WAVE'
wcs_2d.wcs.cunit = 'nm', 'nm'
wcs_2d.wcs.cdelt = 4, 1
wcs_2d.wcs.crpix = 1, 1
wcs_2d.wcs.crval = 3, 1

cube_2d = NDCube(data_2d, wcs=wcs_2d)
cube_2d.crop((7*u.nm, 1*u.nm), (15*u.nm, 1*u.nm))

gives

<ndcube.ndcube.NDCube object at 0x00000165E2AE9490>
NDCube
------
Shape: (3,)
Physical Types of Axes: [('em.wl',)]
Unit: None
Data Type: int64

Screenshots

No response

System Details

==============================
sunpy Installation Information

General
#######
OS: Windows 11 10.0.26100
Arch: 64bit, (Intel64 Family 6 Model 85 Stepping 7, GenuineIntel)
sunpy: 6.1.dev119+g7259b5058.d20240911
Installation path: C:\Users\ayshih\AppData\Local\mambaforge\envs\py312\Lib\site-packages\sunpy-6.1.dev119+g7259b5058.d20240911.dist-info

Required Dependencies
#####################
astropy: 7.0.0.dev810+gb982985335.d20240911
numpy: 2.1.1
packaging: 24.1
parfive: 2.1.0
pyerfa: 2.0.1.4
requests: 2.32.3

Optional Dependencies
#####################
sunpy: 6.1.dev119+g7259b5058.d20240911

Installation method

No response