Optical surfaces

Several parts of the system inputs share the same optical surface control, which defines how a surface reflects, absorbs and scatters light during ray tracing. The same control is used for the standard structure, custom objects, module frames and the ground. This page describes the control and the options behind it.

For the underlying physics, including the spectral treatment and scattering models applied to system surfaces, see System optics.

Selecting a material

A dropdown lists preset materials. The presets available depend on where the control appears:

• For structural components and custom objects, the list contains common construction materials such as galvanised steel, oxidised galvanised steel, concrete, and anodised aluminium alloy.
• For the ground, the presets are grouped into categories (vegetation, soil, snow/water, gravel, construction material) with a specific material within each.

Selecting a preset loads a pre-configured surface: a wavelength-dependent reflectance profile taken from the reflector library, together with default scattering settings. To define a surface that is not in the list, choose Custom.

Show details

Click → Show details to open the surface details dialogue. When a preset is selected the settings are read-only; click → Create custom and edit to unlock them for editing. The dialogue exposes the reflector model and the scattering settings described below, and shows how the selected preset maps to its underlying entry in the reflector library.

Reflector model

A non-Fresnel surface is defined by a reflector, described by its reflectance, absorptance and transmittance (RAT). These always sum to one:

$$R+A+T=1$$

System components and the ground are opaque, so their transmittance is zero and $R+A=1$. Two reflector models are available:

ModelDescriptionConstant with wavelength, A single fixed set of R,, A and T values applied at every wavelength.Wavelength dependent, A measured spectral reflectance profile selected from the reflector library.

Scattering

Reflected light can be scattered using a Lambertian distribution. The scattering fraction sets the proportion of reflected light that is scattered diffusely; the remainder is reflected specularly. System surfaces support Lambertian scattering only, with a single scattering fraction that does not vary with wavelength.

Fresnel surfaces

Instead of a basic reflector, a surface can be defined as a Fresnel material. Use → Switch from reflector to Fresnel in the details dialogue to change the surface type, and → Switch from Fresnel to reflector to change it back. No thin films can be defined on the surface of system components.