Class Name: Image Mapping Function

Superclass - <SEDRIS Abstract Base>

Subclasses

Definition

An instance of this DRM class specifies how the given <Image> instance is to be mapped onto a given textured object, including the mapping method, the projection, and how <Texture Coordinate> instances (if present) are to be treated if they fall outside the image space bounded by the image indexes (0, 0) and (1, 1).

Primary Page in DRM Diagram:

• 22

Secondary Pages in DRM Diagram:

• 4
• 5
• 6
• 8
• 19

Example

1. Consider the visualization of a tree. An image of a tree stored in an <Image> instance is to be mapped onto a rectangular polygon represented by a <Polygon> instance as depicted in Figure 25.

   

   Figure 25 — <DRM Image Mapping Function> example

   The <Polygon> instance is composed of:

   1. an <Image Mapping Function> component associated to the <Image> instance containing the tree data, and composed of a <Presentation Domain> component with presentation_domain = {OTW}. The fields of the <Image Mapping Function> instance are specified as follows:

      image_mapping_method	SE_IMAGMAPMETH_REPLACE
      image_wrap_s	SE_IMAGWRAP_CLAMP
      image_wrap_t	SE_IMAGWRAP_CLAMP
      image_projection_type	SE_IMAGPROJTYP_PLANAR
      intensity_level	1.0
      gain	0.0
      image_detail_mapping	SE_TRUE

   2. four <Vertex> components, where each <Vertex> component is composed of:

      1. An <LSR 3D Location> component specifying the location coordinate of the <Vertex> instance, and
      2. A <Texture Coordinate> component specifying the texture coordinate of the vertex onto the texture map. The texture coordinate values for each vertex map to the [0.0, 0.0], [1.0, 1.0] range of texture coordinate space.

2. Consider a <Polygon> instance with two <Image Mapping Function> components. One <Image Mapping Function> component specifies the <Image> instance displayed for most cases. The second <Image Mapping Function> component, if instance, if image_detail_mapping is SE_TRUE, specifies the imagery that is added to the <Polygon> instance when the eyepoint is so close to the <Polygon> instance that the main <Image> instance texels are no longer useful for texturing the <Polygon> instance.

3. Considering <Polygon> instance D representing the door of a truck that is painted brown, where the door has a forestry service logo on it. D has an <Inline Colour> component that colours the polygon brown and an <Image Mapping Function> component F that texture maps the logo onto the surface of the door representation as follows.

   F has image_mapping_method = SE_IMAGMAPMETH_DECAL.

   The logo image has SE_IMAGSIG_123COLOUR_ALPHA signature. The logo portion of the image has alpha = 1, the border of the logo has alpha = 0.5, and the background of the image outside the logo has alpha = 0.0. When F is applied to the surface of D, therefore, the logo replaces the brown colour since it has alpha = 1, the background of the logo is replaced by the brown colour since it has alpha = 0, and the border of the logo blends the logo colour with the brown colour since it has alpha = 0.5.

FAQs

What is the order of precedence for mapping an <Image> instance to a geometric object, such as a <Polygon> instance?

The <Texture Coordinate> instances on the attribute geometry always have the highest precedence. Next, if the attribute geometry has <Tack Point> instances, three conditions could occur.

1. If there is only one <Tack Point>, the <Tack Point> is used to locate the imagery, and the scaling and rotation information from the <Image Mapping Function> is used.

2. If two <Tack Point> instances are defined, the location and rotation of the imagery is taken from the <Tack Point> instances, but the scaling information is derived from the <Image Mapping Function>.

3. If there are three or more <Tack Point> instances, the position, rotation information is derived from the first three <Tack Point> instances. Since <Tack Point> components are unordered, the complete set of supplied <Tack Point> components shall define an orthogonal image projection. This is to insure that no matter which three <Tack Point> components are used, the same projection is derived for the imagery.

If the <Polygon> does not have <Texture Coordinate> or <Tack Point> components, then any <Image Anchor> components of the <Image Mapping Function> define the location of the image on the attribute geometry. If none of the previous conditions are met, then the <Image Anchor>s in the <Image> are used. If there are no <Texture Coordinate>s, no <Tack Point>s, no <Image Anchor>s in the <Image Mapping Function> and no anchor points in the <Image>, then the image mapping is undefined. It should be noted that the final two cases can be used to create non-orthogonal projections.

How can a non-orthogonal projection of texture be created onto a textured object, e.g., a <Polygon>?

Since all texture mappings that are a result of texture coordinate mapping at the polygon level are defined to be orthogonal projections, a non-orthogonal projection cannot be created with <Texture Coordinate> instances.

To create a non-orthogonal projection, the <Image Anchor> components shall be used. These points are defined in the currently scoped SRF, and therefore are not required to be in the plane of the <Polygon> instance. There is no method to create a non-orthogonal projection in the local SRF of the <Model> instance.

Consider a data provider with a texture map that is applied to a textured object using a spherical projection. How are the centre and radius of projection stored in the <Image Mapping Function> instance?

Rather than using <Texture Coordinate> instances to tie the <Image Mapping Function> instance to the textured object, use an <Image Anchor> instance. For a spherical projection, the <Location> components of the <Image Anchor> instance are interpreted as follows:

1. origin (the centre of the sphere)
2. direction (point on the north pole of the sphere)
3. alignment (point at the equator of the sphere)

Given an <Image> that is to be applied to a given object using a cylindrical projection, how can an <Image Mapping Function> instance be used to store the centre of projection?

The <Image Mapping Function> instance for this case specifies an <Image Anchor> component, while the object to be textured does not specify <Texture Coordinate> instances. For details of how the <Image Anchor> instance specifies the cylindrical projection, see the <Image Anchor> class.

When <Image Anchor> instances are used, how are the rotation and scale of the image mapping represented?

The rotation and scale of the image mapping can be derived from the <Location> instances representing the 3 corners of the <Image> instance, i.e., the <Location> components of the <Image Anchor> instance.

When blending, how do is a blend (luminance) value interpreted?

1.0 = 100% Primary colour, No Blend contribution
0.0 = no Primary contribution, %100 Blend Colour

Does an <Image Mapping Function> apply to both sides of a <Polygon>, or only the front side? What if a data provider wants to represent a wall with brick texture on one side and wallpaper texture on the other?

An <Image Mapping Function> instance applies only to the front side of a <Primitive Geometry>. In the wall example, two <Polygon> instances are needed, one with brick texture on its front side, facing the outside of the building, and the other with wallpaper, facing the inside of the building.

Any other representation would be lost in a rendering system that used back-face culling.

Constraints

• <<Publishable Object>>
• <<Image Anchor SRF>>
• <<Image Mapping Functions and Texture Coordinates>>
• <<Presentation Domain Constraints>>

Associated to (one-way)

• one <Image> instance

Composed of (two-way)

• zero or one <Image Anchor> instance
• zero or one <Presentation Domain> instance

Component of (two-way)

• zero or more <Aggregate Feature> instances
• zero or more <Aggregate Geometry> instances
• zero or more <Data Table> instances
• zero or more <Primitive Feature> instances
• zero or more <Primitive Geometry> instances
• zero or more <Property Set> instances

Inherited Field Elements

Field Elements

Notes

Fields Notes

image_mapping_method

The image_mapping_method field specifies how to combine the referenced texture map with any <Colour> instances on the textured object.

image_wrap_s

The image_wrap_s field specifies whether to clamp or repeat the given <Image> instance in s.

image_wrap_t

The image_wrap_t field specifies whether to clamp or repeat the given <Image> instance in t.

image_projection_type

The image_projection_type field specifies the type of projection to be used when applying the given <Image> instance to textured objects.

1. If planar projection is specified, the following cases may apply.

   1. The DRM object may have <Texture Coordinate> instances or <Tack Point> instances, in which case <<Image Mapping Functions and Texture Coordinates>> applies.
   2. The <Image Mapping Function> instance may have an <Image Anchor> component.
   3. The <Image> instance may have an <Image Anchor> component.

2. If cylindrical or spherical projection is specified, the DRM object shall not have <Texture Coordinate> instances or <Tack Point> instances. Instead, either the <Image Mapping Function> instance or its <Image> instance shall have an <Image Anchor> component.

intensity_level

The intensity_level field specifies the percent contribution of the <Image Mapping Function> instance to the total effect on the textured object. For an <Image> instance with a colour coordinate component specified by its signature, multiply first, second, and third colour coordinate values within the texels of the <Image> instance by this value.

gain

The value of the gain field is to be added to each colour data value from the texel data of the given <Image> instance to obtain the displayed image.

image_detail_mapping

The image_detail_mapping field specifies whether the <Image Mapping Function> instance is used to describe mapping of a detail image on the textured object.