Terrain Modelling

Quadri is principally designed, such that it allows the user to work directly on the primary data in the terrain model. All the secondary data generated by the program is based on linear interpolation between terrain points of primary data. This is introduced as a principle, since, in practice, we do not achieve sufficient accuracy when using the grid model, for example, when profiling along existing roads. Where exact measurements for shoulder edges, tops of cuttings, bottoms of trenches, property boundaries, houses, etc. are available, it would be desirable to produce these breaklines clearly on the profiles generated. This can only happen when the programs are constantly based on direct use of primary data (surveys) and, as a consequence, the model is used as a primary data model.

Traditional grid modelling is also used for purposes other than road planning, in which soil quantity is calculated in vertical quadrilateral columns. This might be the case for general quantity calculations in virgin terrain, residential areas, contour generation, perspective drawings, etc., or in cases where terrain data are read into the model as a point grid.

Triangulation modelling is a function, which constructs triangles between individual points and any breaklines. These triangles are defined by a mathematical procedure consisting of calculating the smallest triangle, which will fit between three points. If surveyed terrain data are logged as a point grid, this function may be used for profile generation, etc. In addition, individual system modules are based on triangulation modelling, for example contour generation.

A primary data model involves only logged data being saved, with no links or interpolation being carried out during modelling. The principle of the model is terrain lines are used to represent the terrain. A terrain line can consist of two or more terrain points linked together.

• Fast updating of the model.
• User has firm control of the results of the model, since they, in principle, resemble the data entered.
• Easy to use.

• Profile generation heavy on resources.
• Requires understanding of the model's mode of operation in order to obtain meaningful results.

The principle of grid modelling is that it will interpolate at fixed heights along the x and y-axes. The grid size is completely dependent on the type of task being undertaken. For road planning and other related tasks, the normal grid size would be between 2 and 10m.

• Requires little disk space in the machine.
• Quickly generates profiles in the model.

• Loss of much useful information since primary data is not kept.
• Difficult to increase accuracy in critical areas.

This type of modelling is based on linking surveyed points into different sized triangles. A triangle is a simpler geometric element than a rectangle, due to the fact that a flat surface can always be placed between 3 points, but not 4.

• Each surface can be described very precisely by way of a pattern of triangles.
• The number of triangles can vary depending on the complexity of the surface.
• Suitable for generating contour maps.
• Does not add new points and does not destroy logged data.

• Linking the triangles is time-consuming.
• Complex storage structure.