Exchange Terrain

A terrain model describes the shape of the ground surface (terrain) within a defined space. This is achieved by determining the elevation of a number of points of known location within that area relative to a datum level.

There are various approaches that can be used to determine a terrain. These are identified as:

• Using a triangulated irregular network (TIN) in which points may be located according to the rate of change of the terrain (i.e. the more rapidly the terrain changes elevation, the more closely spaced are the points whilst points may be widely spaced for flat terrains). In current practise the TIN is either provided as survey points only (with some optional break lines) and the triangulation is done at the receiving end. or the TIN is given with complete triangulation.
• Using a regular grid of points in which the elevation of each point in the grid is determined. Rectangles formed by adjacent grid points can then be separated into 2 triangles. In the grid model, some extra triangles may be drawn adjacent to the extents of polygon shapes that represent 3D-objects in the terrain (roads, etc.), in order to get a smooth connection between the 3D-objects and the grid.

Information for a terrain model may come from a map source (where the terrain is already known) or from a survey (where a terrain needs to be confirmed). It should include:

• A specification of the area for which the terrain is defined in terms of its boundary
• Identification of each significant point within the terrain. This may be either the vertex of a triangle, the other vertices being formed at adjacent points, or a point in a grid.

Triangles are interpreted as planar surfaces within the terrain.
For the purposes of information exchanged, a terrain is considered to be specified within the boundary of the defined space. Specification of the points and the triangles that define the terrain are the same regardless of whether a TIN model or a grid model is used.

Information Requirements

Results