The Severn Partnership, Shrewsbury.
Prior to the commencement of upgrade work on the 267 kilometre Dublin to Cork railway, the Severn Partnership was commissioned to provide an engineering-grade mapping grid for the entire route along with 12 primary control pairs, 53 secondary control pairs, and over 400 photo control points (PCPs) for an aerial mapping campaign.
The Severn Partnership commissioned the DC08 SnakeGrid for the route, which gave them a continuous coordinate system with a scale factor always within 10 parts per million (ppm) of unity at all points along the track – effectively distortion-free.
On completion of the GNSS campaign, all WGS84 coordinates, based on the ETRS89 datum using the OSI CORS network, were converted through SnakeGrid onto the site grid. With no grid zones or scale factors to manage, it was possible to move quickly onto the reduction of local traverse runs where topographic detail had been surveyed.
Lead surveyor on the project Rollo Rigby commented: “In past projects it would be common to have the aerial dataset computed to the national mapping grid or a custom projection optimised for the mapping route. The ground survey would be completed on a separate engineering grid with a scale factor of 1:1, with the two data sets often being treated as separate entities combined using best fit transformations”.
Managing director of the Severn Partnership (and President of The Survey Association) Mark Combes adds: “Using SnakeGrid gives the aerial mapping the same level of consistency as the ground survey, making combining the datasets a straightforward process. A mapping grid that is compatible with GNSS surveying techniques allows easy database updating in future projects, maximizing its value as an asset to the owner”.