Spectral library resampling question

Hello, I am trying to resample an ENVI spectral library to the wavelengths and bandpass of a sensor.

Input speclib (“envi”): 480 bands covering 0.2 - 2.9 um, micron units Output speclib (“swiris”): 100 bands covering 0.96 - 2.44 um, nm units

There are bad values in the input library, so I tried setting the data ignore value thus,

envi.metadata['data ignore value'] = -1.2300000e+34

but that didn’t appear to have any effect. I don’t know how to set those values to NaN in a SpectralLibrary object.

I converted the BandInfo units of the output to microns:

# Convert swiris BandInfo to micron units to match envi speclib
swiris_bandinfo.centers = [x / 1000. for x in swiris_bandinfo.centers]

swiris_bandinfo.bandwidths = [x / 1000. for x in swiris_bandinfo.bandwidths]

I then tried to create BandResmpler object:

envi_swir2020_resampler = spy.BandResampler(envi.bands, swiris_bandinfo)

I then tried to apply the resampler, but I couldn’t find documentation on how to do so. I tried this:

envi_swiris = envi_swir2020_resampler(envi.spectra)

Error:

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-88-17a4918efcc2> in <module>
----> 1 envi_swiris = envi_swir2020_resampler(envi.spectra)

~\miniconda3\envs\py38\lib\site-packages\spectral\algorithms\resampling.py in __call__(self, spectrum)
    236         Any target bands that do not have at lease one overlapping source band
    237         will contain `float('nan')` as the resampled band value.'''
--> 238         return np.dot(self.matrix, spectrum)

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

ValueError: shapes (100,480) and (439,480) not aligned: 480 (dim 1) != 439 (dim 0)

Could you make any suggestions as to what I am doing wrong here? Thank you in advance…

[tboggs]

Python is a copy-by-reference language so saying a = b just points variable a to whatever b is.

There isn’t currently a copy method for spectral libraries. A relatively safe (but inefficient) way to do it is to save the library and load it into a new variable. A faster (but potentially not future-proof) way is to do this:

new_speclib = SpectralLibrary(np.array(old_speclib.spectra), header=old_speclib.metadata)

[pythonic2020]

This seems to have done the trick:

envi.spectra[18]
>>array([-1.2300000e+34, -1.2300000e+34,  1.7548670e-01,  1.9984178e-01,
        2.1063155e-01,  2.1460478e-01,  2.1685915e-01,  2.1990111e-01,
        2.2058058e-01,  2.2873949e-01,  2.3561078e-01,  2.4390015e-01,
        2.5014159e-01, -1.2300000e+34, -1.2300000e+34, -1.2300000e+34,
       -1.2300000e+34,  2.9385823e-01,  3.0357128e-01,  3.1490511e-01,...

envi.spectra[envi.spectra == -1.2300000e+34] = np.nan

envi.spectra[18]
>>array([       nan,        nan, 0.1754867 , 0.19984178, 0.21063155,
       0.21460478, 0.21685915, 0.21990111, 0.22058058, 0.22873949,
       0.23561078, 0.24390015, 0.2501416 ,        nan,        nan,
              nan,        nan, 0.29385823, 0.30357128, 0.3149051 ,
       0.32507223, 0.33639374, 0.34811777, 0.35825697, 0.3682927 ,
       0.37476093, 0.38296247, 0.38948968, 0.3960724 , 0.4032488 ,...