The SEDRIS Data Representation Model
APPENDIX B - Constraints
Image Mapping Functions and Texture Coordinates

Definition

The number of <Image Mapping Function> instances referenced by a <Geometry Representation> instance shall equal the number of <Texture Coordinate> components for each <Vertex> instance and <Tack Point> instance within the component tree rooted at that <Geometry Representation> instance.

<Image Mapping Function> instances referenced by <Feature Representation> instances, on the other hand, shall either have <Image Anchor> components, or reference <Image> instances that have <Image Anchor> components.

EXCEPTION:
If an <Image Mapping Function> instance is used to specify a non-planar projection (such as spherical, cylindrical), it shall use an <Image Anchor> component, and the <Geometry Representation> instance to which the <Image Mapping Function> instance is attached cannot have <Texture Coordinate> instances or <Tack Point> instances within its component tree.

Rationale

The multiple <Image Mapping Function> instances and multiple <Texture Coordinate> instances are ordered, and are defined to correspond to each other as if they were in parallel arrays.

<Image Mapping Function> instances referenced by a <Feature Representation> instance are attributes for geometry that is to be derived by the consumer for the <Feature Representation> instance. Since <Texture Coordinate> instances and <Tack Point> instances are not applicable to <Feature Representation> instances, such <Image Mapping Function> instances shall be specified with <Image Anchor> components.

Example

  1. Consider a triangular <Polygon> instance with one <Image Mapping Function> instance for the OTW domain as shown in Figure 1. Each of the three <Vertex> components of the <Polygon> instance has one <Texture Coordinate> component, specifying the (s,t) within the image space that will be mapped to that <Vertex> instance.

    Image_Mapping_Functions_and_Texture_Coordinates, Ex 1

    Figure 1 — <DRM Image Mapping Functions and Texture Coordinates> example1

  2. Consider a triangular <Polygon> instance that has different texture maps, one for OTW and one for thermal, as shown in Figure 2. The <Polygon> instance thus has two ordered <Image Mapping Function> components, so each of its <Vertex> components will have two ordered <Texture Coordinate> components, one for each <Image Mapping Function> instance.

    Image_Mapping_Functions_and_Texture_Coordinates, Ex 2

    Figure 2 — <DRM Image Mapping Functions and Texture Coordinates> example2

FAQs

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