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. For a <DRM Reference Vector> instance with a <DRM Reference Vector Control Link> component X, the value of the unit_vector field is obtained from X.

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

Class diagram

Figure 6.269 — DRM_Reference_Vector

Constraints

• Publishable object
• Required reference vector location

Example(s)

• Consider a <DRM Polygon> instance specified in a 3D LSR 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 depicted in Figure 6.270:

  

  Figure 6.270 — <DRM Reference Vector> surface normal example

  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 7.2.61 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> instance). This <DRM Reference Vector> instance has a vector_type of RENDERING_NORMAL.

• Consider a <DRM Polygon> instance F classified as ECC_FENCE, where F is a 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 <DRM Reference Vector> components as depicted in Figure 6.271:

  

  Figure 6.271 — <DRM Reference Vector> radar cross section example

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

• A segment of the road has a retroreflector (a device that reflects emissions back along the incident path irrespective of its angle of incidence) on it and is modelled 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 retroreflector, not the road. This is because radars see the road but infrared see the retroreflector. 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 is represented by a <DRM Reference Vector> instance with vector_type = REFLECTIVITY_EMISSIVITY_NORMAL.

• A vector specifying the direction of illumination of a <DRM Infinite Light> instance is represented by a <DRM Reference Vector> component with vector_type = LIGHT_DIRECTION.