OpenMaterial_ior_data

OpenMaterial_ior_data

This is a proposal for an extension to the Khronos Group glTF 2.0 specification. The goal of this extension is to provide a physically accurate description of the complex index of refraction (IOR) at a given temperature and wavelength range in a look-up table. Values within the range which aren't explicitly listed can be obtained using linear interpolation.

The extension may serve as a blueprint for further material-specific look-up tables referenced from the physical_properties section of the OpenMaterial_material_parameters extension.

In order to use this extension, it has to be listed in the extensionsUsed section of a corresponding material file:

"extensionsUsed" : [
    "OpenMaterial_ior_data"
]

Properties

This extension provides complex IOR data measured at a certain temperature for a certain wavelenght range. The IOR data is assigned to either section "n" (which represents the real part of the IOR) or section "k" (representing the imaginary part of the IOR) depending on their affiliation. "n" and "k" are keys to arrays of tuples [wavelength, IOR data].

Within the following enlistment of properties specified by the proposed extension, items labeled as required are mandatory and must be present. Properties without required label are optional and may be omitted:

• temperature [number][required] Temperature [K] at which the IOR values were measured.
• n [array][required] Real part of the IOR, key to an array of tuples of corresponding wavelengths [m] and IOR values [-].
• k [array][required] Imaginary part of the IOR, key to an array of tuples of corresponding wavelengths [m] and IOR values [-].

Example

Within the section physical_properties of its OpenMaterial_material_parameters section, a material file (e.g. aluminium.gltf) provides an URI to a IOR data file:

"materials": [
    {
        "name": "aluminium",
        "extensions": {
            "OpenMaterial_material_parameters": {
                "user_preferences": {
                    ...
                },
                "physical_properties": {
                    "refractive_index_uri": "data/aluminium_ior.gltf", <======
                    ...
                }
            }
        }
    }
],

The IOR data file (in this case aluminium_ior.gltf) provides the data to compute reflections of rays at the geometry:

"extensions": {
	"OpenMaterial_ior_data": {
		"data": [
			{
				"temperature": 300.0,
				"n": [
					[200e-9, 0.110803374],
					...
					[1700e-9, 1.584018511]
				],
				"k": [
					[200e-9, 1.908606137],
					 ...
					[1700e-9,15.55632073]
				]
			}
		]
	}
},

glTF Schema Updates

N/A

JSON Schema

OpenMaterial_ior_data.schema.json

Known Implementations

N/A