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For this type of project, the curvature of the earth is significant and conventional mapping and coordinate systems have to introduce distortions in order to be able to represent the work on a horizontal plane. This then leads to problems when relating 2D designs to the actual construction on the ground. The SnakeGrid algorithm gets around this by providing a single seamless coordinate system with a scale factor within a few parts per million of unity all along the route and for several kilometres on either side – even for projects that extend for hundreds of kilometres.
Effectively, this means that all computations on the project can be treated using a ‘flat earth’ assumption, eliminating the need for corrections and adjustments, and reducing the possibility of costly misunderstandings.
SnakeGrid is used on all major rail routes in the UK, and on some overseas projects. The algorithms it develops are incorporated into software and equipment by most of the major survey manufacturing companies.
Over the last year, several new SnakeGrid coordinate systems have been adopted, including one for a major pipeline project in Cumbria. A new software suite called SnakeGrid Projector has also been developed for Network Rail as a plug-in to Feature Manipulation Engine software (FME), enabling Network Rail to transform data of many different types and in many different formats, between the different coordinate systems that they use.
A paper on SnakeGrid, ‘The development and analysis of quasi-linear map projections’, was published in Cartography and Geographic Information Science (May 2017).
Surveyors and engineers usually have to use correction terms to account for the difference between 2D plans and the real earth. This leads to the possibility of mistakes, and is difficult to implement for very long projects. SnakeGrid gets around this by ‘unpeeling’ the earth along the length of the project, a bit like unpeeling an apple or an orange - but using mathematical algorithms, rather than a knife!
