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.

Class diagram

Figure 6.253 — DRM_Reference_Vector

Constraints

• Publishable Object
• Required Reference Vector Location

Example(s)

• Consider a <DRM Polygon> specified in a 3D LSR spatial reference frame, 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>. The data provider specifies this vector information as a <DRM Reference Vector> component of the <DRM Polygon> as follows:

  

  Figure 6.254 — <DRM Reference Vector> example

  Note that since the <DRM Reference Vector> is a component of a <DRM Polygon>, it specifies an <DRM LSR 3D Location> component in order to comply with Required Reference Vector Location.

• A <DRM Reference Vector> contained by a <DRM Polygon>, representing a normal vector that is used for rendering purposes, i.e. 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 below.

  

  Figure 6.255 — <DRM Reference Vector> example

  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.

  

  Figure 6.256 — <DRM Reference Vector> example

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

• A segment of the road has a reflector (actually, a retro-reflector) on it and is modeled as a <DRM Line>. The <DRM Line> 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 because radars see the road but IR (or more obviously, car lights) see the retro- reflector. In this example, the <DRM Line> has four <DRM Reference Vectors> (radar-normal, radar-azimuth, ir-normal, and ir-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.