THE SNAKE PROJECTION: A CUSTOMISED GRID FOR RAIL PROJECTS

摘要

Surveying on large engineering projects such as railway routes presents particular problems in terms of the coordinate system to be used, since they generally extend beyond the limit of an acceptable site grid. This paper presents a method for tailoring a projection in such a way that the scale factor is always close to unity within a few kilometres of a very long but gently sinuous construction project. It also corrects for height scale factor, and the result is that engineers using automated techniques can effectively ignore scale factor and height above sea level corrections when working on the project. This is now used by Network Rail contractors on the East Coast and West Coast main lines, where the scale factor on the track has been kept within ± 20 ppm of unity along a route of several hundred kilometres. The software has been developed to be applied to any railway project, but also has potential to be used on projects of similar geometry, such as major pipeline routes.