Return a copy of an R object with its class set to a given type of spectrum.
See also
Other constructors of spectral objects:
as.calibration_spct(),
as.chroma_spct(),
as.cps_spct(),
as.filter_spct(),
as.generic_spct(),
as.object_spct(),
as.reflector_spct(),
as.response_spct(),
as.solute_spct(),
as.source_spct(),
source_spct()
