Units
Unless otherwise noted in the documentation, WSF will utilize meter/kilogram/second units for all arguments and member variables. The input system provides the mechanism for the user to specify input values in various forms, but it always converts them to the preferred units before storing them in memory.
The units are as follows:
- Length: meters (m)
- Mass: kilogram (kg)
- Time: seconds (s)
- Velocity: m/s
- Acceleration: m/s^2
- Frequency: Hertz (Hz) = 1/s
- Force: Newtons (Nt) = kg-m/s^2
- Power: Watts (W) = Nt-m/s
- Angle: radians
- Latitude: decimal degrees in the range [-90, 90]
- Longitude: decimal degrees in the range [-180, 180]
- Data units: bits
- Data transfer rate: bits/second
Coordinates
WSF utilizes the coordinate systems as defined by the IEEE Standard for Distributed Interactive Simulation (DIS) - Application Protocols (IEEE Standard 1278.1-1995). The standard defines two basic coordinate systems and WSF adds three additional systems for convenience. The coordinate systems are defined as follow:
- The 'World Coordinate System' (WCS). This is defined to be the WGS-84 coordinate system as defined in NIMA TR 8350.2 and utilized by DIS. This is a right handed with:
- The origin is at the center of the Earth.
- The +X axis passes through 0N, 0E
- The +Y axis passes through 0N, 90E
- The +Z axis passes through 90N (the north pole).
- The 'Entity Coordinate System' (ECS). This is sometimes referred to as the 'Body' coordinate system. This is a right handed system with:
- The origin is at the center of the body.
- The +X axis goes out the front of the body.
- The +Y axis goes out the pilots right side.
- The +Z axis goes out the bottom of the body.
- Positive yaw is to pilots right.
- Positive pitch is nose up.
- Positive roll is right wing down.
- A local North-East-Down (NED) system. This is like the ECS except it has not been rotated by the entity orientation angles.
- The origin is at the center of entity.
- The +X axis is North.
- The +Y axis is East.
- The +Z axis is down.
- The 'Earth Centered Inertial (ECI). This system is like WCS with the exception that it is rotated by an angle that changes with time in the WCS X-Y plane. This also is a right handed system with its origin at the center of the Earth, the X-axis pointing toward the vernal equinox, the point at which the Sun's path crosses the Earth's equator from south to north on the 1st day of Spring, March 20th-21st. This point defines the inertial reference to the X-axis in the equatorial plane. The Y-axis is perpendicular to the X-axis in the equatorial plane and the Z-axis passes through the north pole.
- The 'Part Coordinate System' (PCS), represents the local coordinate system of a part attached to the entity, such as an antenna. It represents the position and orientation of this sub-part. It is important to note, the position and orientation of the sub-part is relative to is owning part or parent entity. It is described more fully in UtEntityPart.
Methods to support these systems are defined in the classes UtEntity and UtEntityPart. The main platform class in WSF (WsfPlatform) derives from UtEntity. UtEntityPart is used by the aggregate parts of the platform to represent the positions of sensors, etc.
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