# Angle variable spectrum

An angle variable spectrum describes, as its name suggests, a spectrum that depends on an angle between 0° and 90°, generally an angle of incidence. It is used by various nodes, such as Mixed tabulated interface law

The data is provided as a list of spectra representing the values between normal and grazing incidence. The scale and interpolation formula can be of three types:

• Angle scale : the first spectrum is the value at θ=0° (normal incidence) and the last one is the value at θ=90° (grazing incidence). Intermediate spectra correspond to values at evenly spaced angle values between 0° and 90°.
• Cosine scale : the first spectrum is the value at cos θ=0 (grazing incidence) and the last one is the value at cos θ=1 (normal incidence). Intermediate spectra correspond to values at evenly spaced cosine values between 0 and 1
• Schlicks scale : the first spectrum is the value at θ=0° (normal incidence) and the last one is the value at θ=90° (grazing incidence). Intermediate spectra correspond to angles at evenly spaced (1-cos θ)^5 values. This is a generalization to the Schlick's approximation

## Children

This node is a spectrum list. It may have a variable number of spectrum children, named "1", "2", "3", etc...

"n"
Spectrum : The nth spectrum in the list

## Parameters

scale
list
The angular scale, must be angle, cos or schlicks

## Ocean XML 2.0 example

``` ```

``` <avspectrum type="" name="lobe" scale="angle"> <spectrum type="tabulated" name="1">4E-7 192.2 5E-7 223.4 6E-7 236.9 7E-7 245.3</spectrum> <spectrum type="tabulated" name="2">4E-7 1.430 5E-7 1.796 6E-7 1.618 7E-7 1.434</spectrum> <spectrum type="tabulated" name="3">4E-7 0.971 5E-7 1.330 6E-7 1.230 7E-7 1.113</spectrum> <spectrum type="tabulated" name="4">4E-7 0.627 5E-7 0.943 6E-7 0.888 7E-7 0.824</spectrum> </avspectrum> ```