8.5 Material brdf schema

8.5.1 metadata

The key meta information about the BRDF look-up table.

Type: object
Required: Yes

8.5.1.1 name

The display name of the material, such as 'Red brick' or 'Dark asphalt'.

Type: string
Required: Yes

8.5.1.2 description

Short description of the material in 2 - 3 sentences.

Type: string
Required: No

8.5.1.3 uuid

Universally unique identifier for the material in 8-4-4-4-12 format, see en.wikipedia.org/wiki/Universally_unique_identifier. The uuid stays the same, even if version is updated.

Type: string
Pattern: \\b[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{12}\\b$
Required: Yes

8.5.1.4 materialVersion

The version number of the material, following semantic versioning (e.g., '1.0.0').

Type: string
Pattern: ^\\d+\\.\\d+\\.\\d+$
Required: Yes

8.5.1.5 openMaterialVersion

The version of the OpenMATERIAL 3D specification used, adhering to semantic versioning (e.g., '1.0.0').

Type: string
Pattern: ^\\d+\\.\\d+\\.\\d+$
Required: Yes

8.5.1.6 copyright

Type: string
Required: Yes

8.5.1.7 license

Describes the license for material distribution. Use an SPDX identifier for open-source licenses (e.g., 'MIT'), or provide a URL or filename for proprietary licenses.

Type: string
Required: Yes

8.5.1.8 author

Lists the author(s) of the material as a name, email, or company. Multiple authors should be comma-separated.

Type: string
Required: Yes

8.5.1.9 creationDate

The date and time of material creation, formatted as YYYYMMDDTHHMMSSZ according to ISO 8601 (e.g., '20240703T101728Z').

Type: string
Pattern: ^\\d{8}T\\d{6}Z$
Required: No

8.5.1.10 source

Source of the BRDF data. Was is measured, simulated, or taken from literature?

Type: string
Required: Yes

8.5.1.11 typicalSensorTechnology

Typical sensor technology this BRDF table is used for, e.g., radar, lidar, camera. If multiply apply, use comma-separation.

Type: string
Required: No

8.5.2 brdf

The BRDF is used as a basic quantity to characterize the reflecting properties of a surface geometrically. The following BRDF definition applies: “The ratio of the radiance or power per unit solid-angle in the outgoing direction from a unit projected surface area to the collimated irradiance or power per unit projected surface area.” A physically plausible BRDF shall additionally obey the following three properties. (1) Positivity: The BRDF has units of inverse steradians (1/sr) and can vary from 0 to infinity. (2) Helmholtz reciprocity: It is symmetric in the incoming and outgoing direction. (3) Energy conservation: No more radiant energy is reflected from a point on the surface than incident radiant energy to that point.

Type: object
Required: Yes

8.5.2.1 wavelengths

List of all wavelengths in meters contained in the lookup table.

Type: array
Required: Yes

8.5.2.2 lookupTable

Array of bidirectional reflectance distribution function (BRDF) values. The array SHALL be sorted based on the columns starting with the first.

Type: array
Required: Yes

Columns of the table:

Column 1: Wavelength of radiation in meters.
Column 2: Incident elevation angle (= zenith angle) relative to the surface normal in rad.
Column 3: Exit elevation angle (= zenith angle) relative to the surface normal in rad.
Column 4: Exit azimuth angle in rad. For BRDFs with incident and exit vectors on the same plane as the normal, exit azimuth angle is 0.
Column 5: BRDF value in 1/sr.