Survey Methodology

The dotted lines show two different alternatives of the order in which the points should be surveyed. Using this method, several staff carriers can be used at the same time.

It is strongly recommended that land surveyors familiarizes themselves with Digital Terrain Model working practices before commencement of any work in the field.

Lines, which are to be the basis for profile generation, must follow the breaklines in the terrain. Linear interpolation should be carried out along a terrain line between sequential points in the line. If the height cannot be interpolated by the linear method, the line MUST be broken.

Measurement points for which linear interpolation between sequential logged points would not be the correct method, should be regarded as individual points and should be imported as random points. Instead, it is recommended that lines be surveyed, since this method of surveying also contains height information between the points.

In general, feature lines in the terrain must be logged in addition to contours, situation charts, etc. Moreover, additional lines should be included in flat areas or where, for other reasons, profiling would incur problems in cutting terrain lines.

The dotted lines display extra lines, which can be surveyed to advantage to reinforce the model in flat areas. In the case of road projections, these extra lines ought mainly to be surveyed along the track of the road.

Dotted lines indicate current additional or reinforcing lines. This type of line could possibly be included, when on-screen digitizing is used.

When surveying existing roads, the following breakpoints should be included in the road profile:

For specialist use, it might be necessary to survey several terrain lines in the road carriageway (e.g. tracking wear on the road).

At intersections it is often desirable to make profiles in all directions. In order to obtain the best possible rendering of the intersection, the surveys should be organized in accordance with the following principle:

Kerbstones and walls should be surveyed as separate bottom and top terrain lines, separated by a number of centimeters, so that profiling takes in the bottom and the top in the correct order. Always ensure that the curbstone top is surveyed before the bottom, since Digital Terrain Model cannot handle overhangs.

Automatic smoothing can be carried out on data import. Smoothing of this type should be carried out when traffic islands or curbstones are being surveyed at intersections, etc., in places where the curve radius is so small that straight-lines between survey points give the wrong impression of the shape of the curve. This is done by inserting the codes for Start Smoothing and Stop Smoothing in the terrain data file before data import. The Start Smoothing and Stop Smoothing code can be included selectively for individual curves.