Class

• <DRM Reference Vector>

Superclass

• <DRM SEDRIS Abstract Base>

Subclass

• None.

Definition

An instance of this DRM class specifies a unit vector, the meaning of which is specified by its vector_type field.

The unit_vector field specifies the unit vector.

The vector_type field specifies the semantic meaning of the vector data being represented by the given instance of <DRM Reference Vector>.

Class diagram

Figure 6.257 — DRM_Reference_Vector

Constraints

• Publishable Object
• Required Reference Vector Location

Example(s)

• Consider a <DRM Polygon> instance specified in a LSR 3D SRF, for which a data provider wishes to explicitly provide the surface normal vector so that consumers do not need to calculate the surface normal when consuming that particular <DRM Polygon> instance. The data provider specifies this vector information as a <DRM Reference Vector> component of the <DRM Polygon> instance as shown in Figure 6.258:

  

  Figure 6.258 — <DRM Reference Vector> example 1

  Since the <DRM Reference Vector> instance is a component of a <DRM Polygon> instance, it specifies a <DRM LSR 3D Location> component in order to comply with the constraint specified in  6.2.50 Required reference vector location.

• Consider a <DRM Reference Vector> instance contained by a <DRM Polygon> instance, representing a normal vector that is used for rendering purposes (that is, to calculate colour and shading when rendering the <DRM Polygon>). This <DRM Reference Vector> would have a vector_type of RENDERING_NORMAL.

• Consider a <DRM Polygon> instance F that represents an ECC_FENCE, where F is a quadrilateral as shown in Figure 6.259.

  

  Figure 6.259 — Example quadrilateral

  F is instanced on some terrain representation, such that the plane of F is perpendicular to the surrounding terrain.

  F has radar cross sections that are dependent on aspect angles (azimuth and elevation). These aspect angles are defined with respect to F’s normal vector and F’s azimuth vector.

  Consequently, F has two components as shown in Figure 6.260:

  

  Figure 6.260 — Two <DRM Reference Vector> components

  The FACE_NORMAL <DRM Reference Vector> instance is the unit vector that is perpendicular to the plane of F, and that points away from F on its outside face. The Reference_Vector_Type <DRM Reference Vector> instance is the unit vector that lies in the plane of F and points straight up.

• A segment of the road has a retro-reflector on it and is modeled as a <DRM Line> instance. The <DRM Line> instance has a normal vector that is perpendicular to it and an azimuth reference parallel to it. This is sufficient to describe radar cross sections of the road as a function of aspect angles. However, the normal vector for the infrared bands depends on the orientation of the retro-reflector, not the road. This is because radars see the road but infrared see the retro- reflector. In this example, the <DRM Line> instance has four <DRM Reference Vector> components (radar-normal, radar-azimuth, infrared-normal, and infrared-azimuth).

• A normal vector used for reflectivity/emissivity calculations. This would have a vector_type of REFLECTIVITY_EMISSIVITY_NORMAL.

• A vector specifying the direction an <DRM Infinite Light> illuminates. This would have a vector_type of LIGHT_DIRECTION.