Rule Name: Image Mapping Functions and Texture Coordinates

Definition

The number of Image Mapping Functions a Geometry object has must be equal to the number of Texture Coordinates for each Base Vertex and Tack Point within that Geometry.

Image Mapping Functions for Features, on the other hand, must either have Image Anchor components, or specify Images that have Image Anchor components.

EXCEPTION:
If an Image Mapping Function is used to specify a non-planar projection (e.g., spherical, cylindrical) then it must use an Image Anchor component, and the Geometry to which the Image Mapping Function is attached cannot have Texture Coordinates or Tack Points.

Rationale

The multiple Image Mapping Functions and multiple Texture Coordinates are ordered, and are defined to correspond to each other as if they were in parallel arrays.)

Image Mapping Functions for Features are attributes for geometry that is to be derived by the consumer for the Feature. Since Texture Coordinates and Tack Points are not applicable to Features, such Image Mapping Functions must be specified by Image Anchors.

Example

1. Consider a triangular Polygon with one Image Mapping Function for the OTW (out-the-window) domain. Each of the Polygon's 3 Vertices has one Texture Coordinate, specifying the (s,t) within the image space that will be mapped to that Vertex.

                       <Polygon>
                          <>
        -----------------------------------------------
        |              |             |                |
       <Vertex>    <Vertex>      <Vertex>     <Image Mapping Function>
        <>            <>             <>             (OTW)
        |              |             |
      <Texture     <Texture      <Texture
      Coordinate>   Coordinate>   Coordinate>
   

2. Consider a triangular Polygon that has different texture maps, one for OTW and one for thermal. The Polygon thus has 2 ordered Image Mapping Functions, so each of its Vertices will have 2 ordered Texture Coordinates, one for each Image Mapping Function.

                       <Polygon>
                          <>
        ------------------------------------------------------------------
        |              |             |                                   |
       <Vertex>    <Vertex>      <Vertex>     <Image Mapping Function> --|
        <>            <>             <>             (OTW)                |
        |              |             |                                   |
        |-<T.C.>       |-<T.C.>      |-<T.C.> <Image Mapping Function> --|
        |              |             |              (thermal)
        |-<T.C.>       |-<T.C.>      |-<T.C.>
   

3. See Texture Coordinate Table for examples of how to use Image Mapping Functions with Texture Coordinates specified in tables.

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