Class Name: EC Location 3D

Superclass - Location 3D

Definition

A coordinate within the Augmented Equidistant Cylindrical (AEC) 3D Spatial Reference Frame (SRF).

The Augmented Equidistant Cylindrical projection-based Spatial Reference Frame is a cylindrical projection normally placed tangent to the equator of the Object Reference Model/Earth Reference Model (ORM/ERM). When secant, two rather than a single parallel are defined; alternatively this can be expressed as a "central scale factor" at the equator. The equator is defined by the ORM/ERM. For a standard parallel at the equator, the ratio of scale in the two dimensions is 1:1. For other latitudes, the ratio is determined by the cosine of the latitude of the standard parallel (i.e., increasing latitude results in decreasing spacing of the projected meridians for a fixed spacing of the projected parallels).

The meridians of the Augmented Equidistant Cylindrical 3D SRF are parallel, equally spaced lines, cut at right angles by straight parallels which are equally spaced.

While the projection does not require that a reference longitude be specified, conventional usage is to define a standard meridian, such as Greenwich, thus allowing for relative offsets in the longitudinal direction.

When used to define a 2D coordinate system, the resulting X and Y axes are measured in meters (rather than arc degrees), and a local origin offset is provided. The X axis lies along the standard parallel, increasing in the easterly direction; the Y axis lies along the standard meridian (and therefore perpendicular to the equatorial parallel), increasing in a northerly direction, and forms a 2D right-handed coordinate system. The Z axis is oriented perpendicular to the other two axes, and forms a 3D right-handed coordinate system. The origin is defined by the intersection of the parametric standard meridian, the parametric standard parallel, and the parametric vertical datum.

For a spherical ORM/ERM, the conversion factor between AEC SRF and geodetic SRF coordinates is determined by the radius at the standard parallel (reference latitude) given the specified horizontal datum (e.g., WGS-84, based on the WGS-84 ellipsoid). For example, at the Earth equator, the conversion factor would be roughly 111,319 meters-per-arc-degree. For a spherical ORM/ERM, and latitude/longitude measured in radians, the basic projection is formulated as follows where R is the ORM/ERM radius and CSF is the central scale factor:

• x = x_offset + (CSF*R*(lon - origin_longitude)*(cos(origin_latitude)))
• y = y_offset + (CSF*R*(lat - origin_latitude))

See the SEDRIS Spatial Reference Model (SRM) for additional details.

Primary Page in DRM Diagram:

• 15

Example

1. Consider a SEDRIS transmittal constructed from a MultiGen OpenFlight database. The transmittal contains an Environment Root whose ORM/ERM is MultiGen Flat Earth, so its srf_params field is specified in Equidistant Cylindrical with horizontal_datum = SE_SPHERICAL_MFE_HDATUM and vertical_datum = SE_SPHERICAL_MFE_VDATUM (MultiGen "flat Earth" horizontal and vertical datums).

   An EC Location 3D within this spatial reference frame might be x = 30.0, y = 50.0, z = 100.0.

FAQs

What is the Equidistant Cylindrical Projected Coordinate System?

The Equidistant Cylindrical Projected Coordinate System specifies a single standard parallel (line of latitude) which is used to determine the ratio of spacing between meridians (lines of longitude) and parallels. For a standard parallel of the Equator, the ratio is 1:1. For other latitudes, the ratio is determined by the cosine of the latitude of the standard parallel (i.e., increasing latitude results in decreasing spacing of the projected meridians).

The projected surface can be viewed as being tangent to the Equator. When considered as secant, two rather than a single standard parallel would be required; alternatively this can be expressed as a "scale factor" at the Equator. Unlike the other PCS, the "scale factor" is applied identically to both dimensions.

While the projection does not require that a reference longitude be specified, conventional usage is to define a standard meridian, such as Greenwich, thus allowing for relative offsets in the longitudinal direction.

Additionally, in M&S (modeling and simulation) applications, the resulting X and Y axes are usually measured in meters (rather than arc degrees). For a spherical ERM, the conversion factor is determined by the Earth radius at the standard parallel (reference latitude) given the specified horizontal datum (e.g., WGS-84, which is based on the WGS-84 ellipsoid). For example, at the Equator, the conversion factor would be roughly 111,319 meters-per-arc-degree. For a spherical ERM, and latitude/longitude measured in radians, the basic projection is formulated as follows where R is the Earth radius and CSF is the central scale factor:

x = x_offset + (CSF*R*(lon - origin_longitude)*(cos(origin_latitude))) y = y_offset + (CSF*R*(lat - origin_latitude))

Constraints

• Environment Root Spatial Reference Frame
• Locations Under Model

Component of (one-way)(inherited)

• optionally, some Arcs
• optionally, some Base Perimeter Data
• optionally, some Base Reference Vectors
• optionally, some Directional Light Behaviors
• optionally, a Distance Level of Detail Data (notes)
• optionally, some Ellipses
• optionally, some Elliptic Cylinders
• optionally, some Feature Edges
• optionally, a Feature Node
• optionally, some Image Anchors
• optionally, some Labels
• optionally, a Location Table
• optionally, some Morph Points
• optionally, some Point Geometries
• optionally, some Property Grid Hook Points
• optionally, a Reference Origin
• optionally, some Spatial Domains
• optionally, some Spatial Index Related Feature Topologies
• optionally, some Spatial Index Related Features
• optionally, some Spatial Index Related Geometries
• optionally, some Tack Points
• optionally, some Vertices
• optionally, some Vertex with Component Indices
• optionally, some World 3X3s
• optionally, some World Transformations
• optionally, an Attachment Point
• optionally, some Center of Buoyancies
• optionally, some Center of Mass
• optionally, some Center of Pressures
• optionally, a Contact Point
• optionally, some Positional Lights
• optionally, some Separating Planes
• optionally, some Sound Instances
• optionally, some Stamp Behaviors
• optionally, some Volumes
• optionally, some Volume Level of Detail Data
• optionally, some Volume Light Behaviors

Field Elements

Notes

Component of Notes

Distance_Level_of_Detail_Data

 the center point for the LOD test

Fields Notes

x

 in meters; positive eastward

y

 in meters; positive northward

z

 Elevation or height; positive along XY surface normal