Class Name: EC Location 2D

Superclass - Location 2D

Definition

A coordinate within the Equidistant Cylindrical (EC) 2D Spatial Reference Frame.

The 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 Equidistant Cylindrical 2D 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 origin is defined by the intersection of the parametric standard meridian and standard parallel.

For a spherical ORM/ERM, the conversion factor between EC 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 2D within this spatial reference frame might be x = 30.0, y = 50.0.

FAQs

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

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