8.5 Material brdf schema
8.5.1 Overview
This is the documentation about the JSON schema file. The actual file is located in the ASAM OpenMATERIAL 3D GitHub repository.
The following diagram shows the hierarchy of the fields defined in this schema. Fields marked with (R) are required. A field can be optional while some of its children are required. In that case, the required children only have to be filled in if the optional parent field is present.
8.5.2 metadata
The key meta information about the BRDF look-up table.
Type: object
Required: Yes
8.5.2.1 name
The display name of the material, such as 'Red brick' or 'Dark asphalt'.
Type: string
Required: Yes
8.5.2.2 description
Short description of the material in two to three sentences.
Type: string
Required: No
8.5.2.3 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
8.5.2.4 materialVersion
The version number of the material, following semantic versioning (for example, '1.0.0').
Type: string
Pattern: ^\d+\.\d+\.\d+$
Required: Yes
8.5.2.5 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
8.5.2.6 copyrights
Indicates copyright details, including the year and copyright holder (for example, '© 2024 ACME Inc.').
Type: array
Item count: at least 1
Item type: string
Required: Yes
8.5.2.7 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
8.5.2.8 authors
Lists the author(s) of the material as a name, email, or company.
Type: array
Item count: at least 1
Item type: string
Required: Yes
8.5.2.9 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
8.5.3 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 the radiant energy incident to that point.
Type: object
Required: Yes
8.5.3.1 wavelengths
List of all wavelengths contained in the lookup table. Unit: meter (m). The upper limit corresponds to 20 kHz.
Type: array
Item type: number
Item range: [1e-09, 0.01716]
Required: Yes
8.5.3.2 receiverSolidAngles
List of all receiver solid angles used to measure the BRDF data. Unit: steradian (sr). Each solid angle is given as a key-value pair mapped to one of the wavelengths contained in the look-up table. If primary receiver optics are placed in front of the detector, the assumed solid angle defined by the aperture of the optics shall be given here. This field is required by common laser measurement standards, such as SEMI ME1392-0116 (2023) and EN ISO 19986:2020.
Type: array
Required: No
8.5.3.3 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
Column count: exactly 5
Columns of the table:
| Column | Type | Constraints | Description |
|---|---|---|---|
1 |
number or null |
|
Wavelength of the radiation in free space. Unit: meter (m). The upper limit corresponds to 20 kHz. |
2 |
number or null |
|
Incident zenith angle relative to the surface normal, in rad. |
3 |
number or null |
|
Exit zenith angle relative to the surface normal, in rad. |
4 |
number or null |
|
Exit azimuth angle in rad. The value is relative to the incident azimuth angle. The incident azimuth angle is set to 0, because the incident ray is used as the reference. |
5 |
number or null |
|
BRDF value. Unit: inverse steradian (1/sr). The minimum value is 0. |