README.md

OpenMaterial_permeability_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 relative permeability at a given temperature, humidity, incident angle 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_permeability_data"
]

Properties

This extension provides relative permeability data measured at a certain incident angle, temperature and humidity for a certain wavelenght range.

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 permeability was measured.
• relative_humidity [number][required] Relative humidity [%] at which permeability was measured.
• incident_angle [number][required] Incident angle of the measurement relative to the local normal vector at the material surface in [rad].
• permeability [number][required] Relative permeability, key to an array of tuples of corresponding wavelengths [m] and permeability values [H/m].

Example

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

"materials": [
    {
        "name": "tarmac",
        "extensions": {
            "OpenMaterial_material_parameters": {
                "user_preferences": {
                    ...
                },
                "physical_properties": {
                    ...
                    "permeability_uri": "data/tarmac_permeability.gltf", <======					
                    ...
                }
            }
        }
    }
],

The permeability data file (in this case tarmac_permeability.gltf) provides the data to compute permeability at the geometry:

"extensions": {
    "OpenMaterial_permeability_data": {
        "data": [
            {
                "temperature": 300.0,
                "humidity": 80.0,
                "incident_angle": 0.785398,				
                "permeability": [
                    [3.89341e-03, xxx]
				]
            }
        ]
    }
},

glTF Schema Updates

N/A

JSON Schema

OpenMaterial_permeability_data.schema.json

Known Implementations

N/A