Class Name: LTP Location 3D

Superclass - Location 3D

Definition

A coordinate within the Local Tangent Plane (LTP) 3D Spatial Reference Frame.

The Local Tangent Plane Spatial Reference Frame specifies a local Cartesian coordinate system where the XY plane is parallel to a plane tangent to the Object Reference Model/Earth Reference Model (ORM/ERM) specified by a parametrically-defined horizontal datum and reference point. The vertical origin of the tangent plane is specified by a parametrically-defined vertical datum.

For example, the ERM WGS-84 ellipsoid specified by the WGS-84 horizontal datum may define the surface to which the LTP is parallel at the point of tangency; however, Mean Sea Level (MSL) may define the "vertical" displacement of the LTP origin from that point of tangency.

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 direction of the Y axis may be rotated from the local polar direction (e.g., geographic North), and the X axis is defined as forming a 2D right-handed coordinate system. The origin (point of tangency) is defined by the parametric geodetic latitude and longitude. The Z axis is oriented perpendicular to the other two axes (and not necessarily normal to the local vertical datum), and forms a 3D right-handed coordinate system.

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

Primary Page in DRM Diagram:

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Example

1. A Property Grid maps wind velocities along a coastline. The Property Grid uses a Local Tangent Plane spatial reference frame with the Y axis parallel to the coast.

FAQs

How does the Local Tangent Plane (LTP) SRF differ from the Local Space Rectangular (LSR) SRF?

The Local Tangent Plane SRF specifies a location in a georeferenced space. The Local Space Rectangular SRF specifies a location in a Cartesian, non-georeferenced "model" space.

I have a 2D grid. Why do I have to specify a height?

Because the Local Tangent Plane references a Cartesian coordinate system to a curved surface, the two surfaces are not parallel (in particular, LTP is not a projection-based SRF). When they are not parallel, a 2D coordinate in one SRF can map to a range of 2D coordinates in the other SRF. Specifying the third coordinate resolves this ambiguity.

If your grid is small enough or the ambiguity in location is unimportant, you can specify a height as a global parameter of the Property Grid. Otherwise, you should specify the height as a separate value in each grid cell, or use several grids of smaller extents.

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

y

 in meters

z

 Elevation or height; positive along xy surface normal