This method returns a normalized difference index value for an arbitrary pair of wavebands. There are many such indexes in use, such as NDVI (normalized difference vegetation index), NDWI (normalized difference water index), NDMI (normalized difference moisture index), etc., the only difference among then is in the wavebands used.
normalized_diff_ind(spct, w.band.plus, w.band.minus, f, ...)normalised_diff_ind(spct, w.band.plus, w.band.minus, f, ...)
NDxI(spct, w.band.plus, w.band.minus, f, ...)
# S3 method for default
normalized_diff_ind(spct, w.band.plus, w.band.minus, f, ...)
# S3 method for generic_spct
normalized_diff_ind(spct, w.band.plus, w.band.minus, f, ...)
# S3 method for generic_mspct
normalized_diff_ind(spct, w.band.plus, w.band.minus, f, ...)
A named numeric value for the index, or a tibble depending on whether
a spectrum or a collection of spectra is passed as first argument. If
the wavelength range of spct does not fully overlap with both
wavebands NA is silently returned.
an R object
waveband objects The wavebands determine the regions of the spectrum used in the calculations.
function used for integration taking spct as first argument and a list of wavebands as second argument.
additional arguments passed to f
normalized_diff_ind(default): default
normalized_diff_ind(generic_spct):
normalized_diff_ind(generic_mspct):
f is most frequently reflectance, but also
transmittance, or even absorbance,
response, irradiance or a user-defined function
can be used if there is a good reason for it. In every case spct
should be of the class expected by f. When using two wavebands of
different widths do consider passing to f a suitable quantity
argument, for example to compare averages rather than integrals. Wavebands
can describe weighting functions if desired.
$$\mathrm{NDxI} = \frac{f(s, wb_\mathrm{plus}) - f(s, wb_\mathrm{minus})}{f(s, wb_\mathrm{plus}) + f(s, wb_\mathrm{minus})}$$
Rfr_normdiff