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.
Usage
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, ...)
# Default S3 method
normalized_diff_ind(spct, w.band.plus, w.band.minus, f, ...)
# S3 method for class 'generic_spct'
normalized_diff_ind(spct, w.band.plus, w.band.minus, f, ...)
# S3 method for class 'generic_mspct'
normalized_diff_ind(spct, w.band.plus, w.band.minus, f, ...)
Value
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.
Details
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.
$$\mathrm{NDxI} = \frac{f(s, wb_\mathrm{plus}) - f(s, wb_\mathrm{minus})}{f(s, wb_\mathrm{plus}) + f(s, wb_\mathrm{minus})}$$
Methods (by class)
normalized_diff_ind(default)
: defaultnormalized_diff_ind(generic_spct)
:normalized_diff_ind(generic_mspct)
:
Note
Some NDxI indexes are directly based on satellite instrument data, such
as those in the Landsat satellites. To simulate such indexes using spectral
reflectande as input, constructors of waveband
definitions from package
'photobiologyWavebands' can be useful.
normalised_diff_ind()
is a synonym for normalized_diff_ind()
.
NDxI()
is a shorthand for normalized_diff_ind()
.