The Snake Projection is a continuous

map projection In cartography, a map projection is any of a broad set of Transformation (function) , transformations employed to represent the curved two-dimensional Surface (mathematics), surface of a globe on a Plane (mathematics), plane. In a map projection, ...

typically used as the planar

coordinate system In geometry, a coordinate system is a system that uses one or more numbers, or coordinates, to uniquely determine and standardize the position of the points or other geometric elements on a manifold such as Euclidean space. The coordinates are ...

for realizing low distortion throughout long linear engineering projects.

Details

The Snake Projection was originally developed by

University College London University College London (Trade name, branded as UCL) is a Public university, public research university in London, England. It is a Member institutions of the University of London, member institution of the Federal university, federal Uni ...

and

Network Rail Network Rail Limited is the owner (via its subsidiary Network Rail Infrastructure Limited, which was known as Railtrack plc before 2002) and railway infrastructure manager, infrastructure manager of most of the railway network in Great Britain. ...

to provide a continuous low distortion projection for the West Coast Mainline infrastructure works. The parameters defining each Snake Projection are tailored for the specific project. The most typical use is with large-scale linear engineering projects such as rail infrastructure; however, the projection is equally applicable to any application requiring a low distortion grid along a linear route (for example pipelines and roads). The name of the projection is derived from the sinuous snake-like nature of the projects it may be designed for. Typical

distance distortion characteristics of a Snake Projection are minimal over the whole route within approximately of the centre line. The principal advantage of the projection is that, for the corridor defining the design space, distances measured on the ground have a nearly one-to-one relationship with distances in coordinate space (i.e. no scale factor need be applied to convert between distances in grid and distances on the ground). The length of the applicable corridor is variable on a project basis; however, when required, the projection can extend over several hundreds of kilometres to achieve grid distortion of less than 20

parts per million In science and engineering, the parts-per notation is a set of pseudo-units to describe the small values of miscellaneous dimensionless quantity, dimensionless quantities, e.g. mole fraction or mass fraction (chemistry), mass fraction. Since t ...

along the route. The main disadvantage is that away from the design corridor, the distortion of the projection is not controlled. The Snake Projection is suited for engineering purposes due to its low distortion characteristics. An example of its differentiation from mapping grids is the increase in length of the London to Birmingham section of the HS2 rail line, purely due to the more accurate grid representation compared to the length when using the national mapping coordinate system

British National Grid The Ordnance Survey National Grid reference system (OSGB), also known as British National Grid (BNG), is a system of geographic grid references, distinct from latitude and longitude, whereby any location in Great Britain can be described in te ...

Usage

The Snake Projection is the engineering coordinate system used for a significant proportion of primary rail routes in the UK, including that of the HS2 London to Birmingham high speed line. For the London to Glasgow

West Coast Main Line The West Coast Main Line (WCML) is one of the most important railway corridors in the United Kingdom, connecting the major cities of London and Glasgow with branches to Birmingham, Manchester, Liverpool and Edinburgh. It is one of the busiest ...

, the distortion in the Snake Projection used is no greater than 20

within of either side of the track.

Implementation

The Snake Projection algorithm converts between

geographical Geography (from Ancient Greek ; combining 'Earth' and 'write', literally 'Earth writing') is the study of the lands, features, inhabitants, and phenomena of Earth. Geography is an all-encompassing discipline that seeks an understanding o ...

and grid coordinates; however, the method of technical implementation can vary. One method of implementing a Snake Projection is to define using an

NTv2 The NTv2 (National Transformation version 2) is a standard binary grid shift (.GSB) file format. It can transform coordinates between the NAD27 and NAD83 geodetic reference systems for example. The transformation is bidimensional (2D), or horizont ...

geodetic transformation coupled with a standard parameterised map projection (such as

Transverse Mercator The transverse Mercator map projection (TM, TMP) is an adaptation of the standard Mercator projection. The transverse version is widely used in national and international mapping systems around the world, including the Universal Transverse Mercat ...

); this is increasing in popularity due to better compatibility with CAD and

GIS A geographic information system (GIS) consists of integrated computer hardware and software that store, manage, analyze, edit, output, and visualize geographic data. Much of this often happens within a spatial database; however, this is not ...

software. The global

EPSG EPSG Geodetic Parameter Dataset (also EPSG registry) is a public registry of geodetic datums, spatial reference systems, Earth ellipsoids, coordinate transformations and related units of measurement, originated by a member of the European Petr ...

geodetic coordinate system database features several snake projection definitions through the NTv2 approach. Other implementations include those published through the SnakeGrid organisation.

References

{{DEFAULTSORT:Snake Projection Map projections Geodesy Rail infrastructure Surveying Civil engineering

Details

Usage

Implementation

See also

References