Survey Control:
We work to either a local grid, or link to O.S National grid as required. We understand the intricacies of grid transformations, OSGB36, ETRS89, WGS84, scale factors, grids, datums and the implications of utilising Ordnance Survey digital data. A robust survey drawing is always created from a solid network of survey control stations.
This survey control must be stable and well constructed; preferably in a location that will not be moved or lost. The control observations must be taken with care, utilising calibrated instrumentation and computed with regard to redundant observations and inbuilt checks. Once computed and checked, we can document our control for future use with witness diagrams.
Long, thin surveys – Snakegrid
For pipelines, highways and railway projects, we can create a ‘snakegrid‘ which gives an engineering accuracy scale factor of ‘1’ along the centreline of the survey. Perfect for railway and pipeline surveys over tens of kilometers.
Our ability to appreciate the ‘bigger picture’ has resulted in Severn Partnership being responsible for defining control survey grids that run the length of the country (East Coast Main Line grid ECM05). Sometimes a small scale approach does not work on large projects. Scale factor distortion from standard grid projections would be outside the high accuracies demanded for rail track alignment design over long distances.
We can offer bespoke ‘long thin’ grid & datum projection solutions that can be created for specific projects; be they roads, railways or pipelines. The effects of scale in plan and height are taken into account to define trend lines for the ‘snakemaker’ projection. We are then able to observe with static GPS in ETRS89 coordinates and convert them into a local grid using the ‘snakemaker’ program.
This technique can be used for any near-linear projects, anywhere in the world. The net result is survey work carried out without discontinuities between individual different projections.
Glossary:
GPS = Global Positioning System (U.S owned and administeres) GNSS = Global Navigation Satellite Systems (Generic term for geospatial positioning on a global scale) RTK = Real time kinematic OSGB36 = Ordnance Survey Natoinal Grid reference system ETRS89 = European Terrestrial Reference System WGS84 = World Geodetic System (used by GPS / GNSS)