These involve defining in plan form the structure to be constructed making allowance for topographic (relief), hydraulic (crossing of water courses), and geotechnical (soil types) constraints.

Topographic survey by GPS (all rights reserved)

These involve defining in plan form the structure to be constructed making allowance for topographic (relief), hydraulic (crossing of water courses), and geotechnical (soil types) constraints.

Geometric studies begin with a preliminary study on 1/25,000th scale maps and plans, for example, to identify all the possible variant solutions and select out the best. Aerial or satellite photographs are used for this, followed by surveys in the field.

The preliminary study is followed by a draft preliminary design which defines the geometric characteristics of the project with more precision, giving for example typical cross-sections, the engineering principles behind the earthworks, the general outline of the drainage network, brief features of the structures, and, finally, the main quantities that will allow the project costs to be estimated.

The draft preliminary design is followed by the detailed preliminary design which is drawn up once the final solution has been chosen. The detailed preliminary design has specifications of all the dimensions and characteristics of the structure obtained as a result of very accurate topographic surveys carried out over the terrain. Layout calculations are nowadays performed by computer.
Finally the detailed preliminary design allows the execution plan to be drawn up which includes in particular 1/500th scale detail plans, for instance, completely defining the operations to be carried out as well as the means of their execution.

A complex project like the construction of a motorway, or a high speed TGV line, or an earthworks dam, involves teams of topographers, geometers, consultant engineers, designers and project managers over a period of years.