Every 3D model has its own local coordinate system. If TerrainView™ is in modify mode, the local coordinate system of an object is represented by three colored arrows, the red arrow pointing in direction of the local x-axis, the green one in direction of the local y–axis, and the blue one in direction of the local z-axis.
Before attacking the subject of coordinate system initialization and geo-referencing in scenes, some concepts must be explained in order for the meaning of various coordinate systems in TerrainView™ to be understood.
In TerrainView™ two coordinate systems are used for geo-referencing:
The input or scene coordinate system
The output or mapping coordinate system
The scene coordinate system is fixed once for a scene in the “Coordinate System Calibration” dialog. This coordinate system defines the system in which elements of the scene (terrains, 3D models, ...) are referenced.
For example, if a terrain database has been defined in a WGS84 coordinate system by means of a third party tool, then this would be the scene coordinate system.
In other words: Since every entity’s (terrains, 3D models, …) visualization is based on polygons, and since these polygons are specified using a orthogonal 3-dimensional coordinate system, the axes of the entity’s coordinate system are parallel to the axes of the scene coordinate system. How an entity is placed into the scene is illustrated on the next page.
The choice and calibration of the scene coordinate system is used to define a conversion between internal coordinate systems and the employed real coordinate system. Currently, the following coordinate systems are supported *:
Internal (OpenGL) is the definition of a system for which the internal coordinate systems of 3D objects is employed. For technical reasons, the axes are not very intuitive (see illustration on the next page).
Flat Grid is an orthogonal coordinate system transformation that allows translation and scaling. This transformation can be used to map local orthogonal coordinate systems. The mapping is only valid in the corresponding area and can therefore not be transformed into another area or onto geographic coordinate systems.
Normal uses the same origin and scaling as Internal (OpenGL) but has more intuitive axes (see illustration on the next page). This is the default coordinate system until a calibration has been performed.
SwissGrid is Switzerland’s locally defined coordinate system.
WGS84 is the globally defined and well known coordinate system using longitude, latitude and altitude.
UTM is the Universal Transverse Mercator Grid which is divided into several zones.
*) For TerrainView-Globe™ scenes, the coordinate systems FlatGrid and Normal are not supported. These systems are not necessary since the scene is automatically calibrated with WGS84.