Class Name: Reference Vector

Superclass - Base Reference Vector

Definition

A unit vector that is used to specify a direction, normal, or axis in the manner specified by the vector_type field. It serves as a unit vector in those coordinate systems with compatible vector space structure. In GD, GM, GEI, GSE, GSM, and SM coordinate systems, it is a vector in the canonical LTP at the location of the Reference Vector Location component.

Primary Page in DRM Diagram:

• 7

Secondary Pages in DRM Diagram:

• 4
• 5
• 18
• 23

Example

1. A Reference Vector contained by a Polygon, representing its geometric normal vector. This would have a vector_type of SE_FACE_NORMAL.
2. A Reference Vector contained by a Polygon, representing a normal vector that is used for rendering purposes, i.e. to calculate color and shading when rendering the Polygon. This Reference Vector would have a vector_type of SE_RENDERING_NORMAL.
3. A fence modeled as a polygon has radar cross sections that are dependent on aspect angles (azimuth and elevation). These aspect angles are defined with respect to the polygon's normal and its azimuth Reference Vector. This Polygon (fence) has two Reference Vectors (a geometric-normal and an azimuth-reference). The geometric normal is the unit vector perpendicular to the Polygon pointing away from it on its outside face and the azimuth reference vector points straight up and is in the plane of the Polygon.
4. A segment of the road has a reflector (actually, a retro-reflector) on it and is modeled as a Line. The 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 Line has four Reference Vectors (radar-normal, radar-azimuth, ir-normal, and ir-azimuth).
5. A normal vector used for reflectivity/emissivity calculations. This would have a vector_type of SE_REFLECTIVITY_EMISSIVITY_NORMAL.
6. A vector specifying the direction an Infinite Light illuminates. This would have a vector_type of SE_LIGHT_DIRECTION.

FAQs

Why so many different types of Reference Vectors? Aren't all or many of these the same unit vector with different names?

These vectors coincide with each other in many cases, but generally, each each can be unique. For a flat large window, as an example, the geometric normal will coincide with the radar-normal and also the ir-normal, but for complex objects such as an aircraft, geometric-normal is not applicable and radar- and ir-normal does not coincide.

Why can a Base Vertex have only one Reference Vector when a Polygon, Point, or Line can have more than one?

A Base Vertex will not require more than one Reference Vector, but a Polygon may need more than one to represent a combination of geometric and/or sensor-related vectors at the same time. In other words, a side of the building represented as a Polygon, a ship as a Point, or a bridge as a Line require at least two Reference Vectors defined, normal and azimuth, to fully describe aspect dependent characteristics of the physical object represented. Vertices, on the other hand, do not represent these types of physical objects and therefore do not require multiple Reference Vectors. A vertex can have one rendering-normal as used for smooth shading, but has no use for aggregating any other types of Reference Vectors.

Why does Reference Vector have an optional Location component?

To support the ability of the SEDRIS API to automatically convert Reference Vectors between spatial reference frames, including non-vector space coordinates, such as Geodetic.

If a Location component is required for some conversions, why is it an optional component?

In most cases, a Reference Vector will inherit an appropriate Location component. In those cases where an appropriate Location cannot be inherited, a Location component is required by business rules.

See also FAQ in Required Reference Vector Location.

Constraints

• Inheritance Rule For Location
• Required Reference Vector Location

Composed of (one-way)(inherited)

• optionally, a Location

Composed of (two-way)(inherited)

• optionally, a Reference Vector Control Link

Component of (one-way)

• optionally, some Base Vertices
• optionally, some Cylindrical Volume Extents
• optionally, some Ellipses
• optionally, some Elliptic Cylinders
• optionally, some Infinite Lights
• optionally, some Lines
• optionally, some Lobe Data
• optionally, some LSR Transformation Steps
• optionally, some Moving Light Behaviors
• optionally, some Parallelepiped Volume Extents
• optionally, some Points
• optionally, some Polygons
• optionally, some Union of Geometries

Inherited Field Elements