Having recently delivered high accuracy aerial mapping for above ground lines of parts of the London Underground and Docklands Light Rail network, Atkins is now working with Transport for London to supply similar quality data of the above ground Jubilee, Northern and Piccadilly lines for London Underground.

With continuing improvements in large format digital metric aerial cameras, and the right aircraft, Atkins has developed a robust methodology for achieving these very high accuracies which can be deployed for projects in the UK and Europe.

This is a highly cost-effective and accurate methodology to provide aerial mapping for rail, highway or other applications, with the key benefit that the mapping is produced without the need to enter the rail or highway corridor to undertake the works.

“Anything which improves accuracy and reduces the need for surveyors to enter difficult and dangerous locations must be a benefit to the management of large-scale infrastructure projects,” said Nick Chamberlain, geomatics production manager at Atkins.

Across each of these projects, Atkins has employed imagery with a GSD (Ground Sampled Distance) of 2 cm, the highest resolution aerial imagery commissioned by Atkins from a fixed wing aircraft. This very high resolution imagery, combined with calibrated GPSINS exterior orientation data and high quality GPS ground control, has enabled the production of aerial topographic mapping with an absolute 3D accuracy of +/-2 cm RMSE (root mean square error), with the data delivery for the schemes further enhanced by the supply of high quality ortho-rectified imagery.

In addition to the production of the topographic mapping and orthophoto production, Atkins worked closely with the London Underground survey team to refine and improve their ICS survey data format providing seamless data input into the track department’s design software.

“The clarity and detail in this high-resolution imagery provides a level of confidence in the identification and digitisation of features and assets not previously possible with lower resolution imagery or aerial LiDAR. An additional benefit of this high-resolution imagery is that surface type and condition can be more easily identified,” adds Cory Hope, geomatics capability lead at Atkins.

Adrian Lintott at London Underground explained: “The photography and mapping was originally commissioned to meet the requirements of a single project. The method was chosen as a cost-effective way of gathering whole line data sets without the need for physically accessing the railway. It has now become a ‘must have’ for many engineers and planners across Transport for London (TfL).

“Having the data available at a 2cm resolution gives greater confidence, which in turn allows for the feasibility stage of projects to be accelerated. This enables London Underground to deliver upgrade works, such as new rolling stock design and track configuration changes, in shorter timeframes and with less risk when moving from feasibility to design.

“The data is available to all staff in TfL as both mapping and ortho-rectified images and is used on a daily basis.”