"colour.dominant_wavelength" definition seems to struggle with precise spectral locus CMF xy values?

CMFS_1931 = colour.MSDS_CMFS["CIE 1931 2 Degree Standard Observer"]

CMFS_1931_xy = colour.XYZ_to_xy(CMFS_1931.values)
whitepoint = numpy.asarray([0.3101, 0.3163])

discard, locus_1931_samples_xy, discard = \
    colour.dominant_wavelength(
        CMFS_1931_xy,
        whitepoint,
        cmfs=CMFS_1931,
)

/usr/local/lib/python3.7/dist-packages/colour/algebra/geometry.py:326: RuntimeWarning: invalid value encountered in true_divide
  u_a = numerator_a / denominator
/usr/local/lib/python3.7/dist-packages/colour/algebra/geometry.py:327: RuntimeWarning: divide by zero encountered in true_divide
  u_b = numerator_b / denominator
/usr/local/lib/python3.7/dist-packages/colour/algebra/geometry.py:327: RuntimeWarning: invalid value encountered in true_divide
  u_b = numerator_b / denominator
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-40-2288142fce39> in <module>()
     10         CMFS_1931_xy,
     11         whitepoint,
---> 12         cmfs=CMFS_1931,
     14 )

3 frames
/usr/local/lib/python3.7/dist-packages/colour/colorimetry/dominant.py in dominant_wavelength(xy, xy_n, cmfs, inverse)
    194     xy_s = XYZ_to_xy(cmfs.values)
    195 
--> 196     i_wl, xy_wl = closest_spectral_locus_wavelength(xy, xy_n, xy_s, inverse)
    197     xy_cwl = xy_wl
    198     wl = cmfs.wavelengths[i_wl]

/usr/local/lib/python3.7/dist-packages/colour/colorimetry/dominant.py in closest_spectral_locus_wavelength(xy, xy_n, xy_s, inverse)
    117     i_wl = np.argmin(scipy.spatial.distance.cdist(xy_wl, xy_s), axis=-1)
    118 
--> 119     i_wl = np.reshape(i_wl, xy.shape[0:-1])
    120     xy_wl = np.reshape(xy_wl, xy.shape)
    121 

<__array_function__ internals> in reshape(*args, **kwargs)

/usr/local/lib/python3.7/dist-packages/numpy/core/fromnumeric.py in reshape(a, newshape, order)
    297            [5, 6]])
    298     """
--> 299     return _wrapfunc(a, 'reshape', newshape, order=order)
    300 
    301 

/usr/local/lib/python3.7/dist-packages/numpy/core/fromnumeric.py in _wrapfunc(obj, method, *args, **kwds)
     56 
     57     try:
---> 58         return bound(*args, **kwds)
     59     except TypeError:
     60         # A TypeError occurs if the object does have such a method in its

ValueError: cannot reshape array of size 6225 into shape (471,)

[KelSolaar]

Nah, one liner change.

[sobotka]

I arrived at one via Shapely. Not sure if it is relevant or if it could be viable for Colour, but it seems to work pretty well. Essentially create a Shapely polygon from the CMFS, then use the intersection to calculate.

spectral_locus_polygon = shapely.geometry.Polygon(
    CMFS_xyY[:, 0:2]
)

spectral_intersections = []
for line in xy_lines.geoms:
    intersection = spectral_locus_polygon.intersection(line)
    spectral_intersections.append(intersection)