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
8.5.1.3 uuid
Universally unique identifier for the material in 8-4-4-4-12 format, see [12]. 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 (for example, '1.0.0').
Type: string
Pattern: ^\\d+\\.\\d+\\.\\d+$
Required: Yes
8.5.1.5 openMaterial3dVersion
The version of the ASAM OpenMATERIAL 3D specification used, adhering to semantic versioning (for example, '1.0.0').
Type: string
Pattern: ^\\d+\\.\\d+\\.\\d+$
Required: Yes
8.5.1.6 copyrights
Indicates copyright details, including the year and copyright holder (for example, '© 2024 ACME Inc.').
Type: array
Required: Yes
8.5.1.7 license
Describes the license for material distribution. Use an SPDX identifier for open-source licenses (for example, 'MIT'), or provide a URL or filename for proprietary licenses.
Type: string
Required: Yes
8.5.1.8 authors
Lists the author(s) of the material as a name, email, or company.
Type: array
Required: Yes
8.5.1.9 creationDate
The date and time of material creation, formatted as YYYYMMDDTHHMMSSZ according to ISO 8601 [8] (for example, '20240703T101728Z').
Type: string
Pattern: ^\\d{8}T\\d{6}Z$
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. The wavelength values shall be within the range of 1e-09 to 17.16e-03 (upper limit corresponds to 20 kHz).
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 free-space in meters (m). The value shall be within the range of 1e-09 to 17.16e-03 (upper limit corresponds to 20 kHz).
-
Column 2: Incident zenith angle relative to the surface normal in rad. It shall be within a range of \(0\) to \(\pi/2\).
-
Column 3: Exit zenith angle relative to the surface normal in rad. It shall be within a range of \(0\) to \(\pi/2\).
-
Column 4: Exit azimuth angle in rad. It shall be within a range of \(0\) to \(2 \pi\). The value is relative to the incident azimuth angle. The incident azimuth angle is set to 0° as the incident ray is used as reference.
-
Column 5: BRDF value in 1/sr. The minimum values is 0.