Function to set by reference the "Rfr.type" attribute of an
existing reflector_spct or object_spct object, and function to
query its current status.
Usage
setRfrType(x, Rfr.type = c("total", "specular"))
getRfrType(x)Value
x, with the modified attribute in the case of setRfrType() or
the character value, "total" or "specular", stored
in the "Rfr.type" attribute of x in the case
of getRfrType(). If x is not a reflector_spct or
an object_spct object, NA is returned.
Details
Reflectance can be measured by collecting the light reflected out of a surface in all directions, using an integrating sphere, obtaining a quantity called total reflectance. If instead, the reflected light is collected at a narrow angle mirroring the incident angle, only part of the reflected radiation is collected, corresponding to mirror-like reflection, called specular. Thus,
$$\rho = \rho_s + \rho_d$$
where, \(\rho\) is total reflectance, and its components, \(\rho_s\), specular reflectance, and \(\rho_d\), diffuse or scattered reflectance. When strong scattering takes place, total reflectance can be much more than the specular component. In most cases \(\rho_d\) is not measured directly.
The distinction depends on the measuring procedure, and this information is
stored as metadata in an attribute of objects of classes
reflector_spct or an object_spct.
When converting between internal and total transmittance, or computing absorptance by difference based on transmittance and reflectance, only total reflectance can be meaningfully used (if the object does not noticeably scatter light, it may be possible to assume that specular reflectance represents most of the total reflectance.) Consequently, checking the stored value of this attribute is used as a safeguard in these compuations.
This attribute is normally set when the source_spct object
is created.
Note
Function setRfrType() alters x itself by reference and in
addition returns x invisibly. If x is not a
reflector_spct or an object_spct object, x is not
modified. The behaviour of this function is 'unusual' in that the default
for parameter Rfr.type is used only if x does not already
have this attribute set.
Examples
my.spct <- reflector_spct(w.length = 400:409, Rfr = 0.1)
getRfrType(my.spct)
#> [1] "total"
setRfrType(my.spct, "specular")
getRfrType(my.spct)
#> [1] "specular"