N11/M11 Junction 4 to Junction 14 Upgrade Project – Topographical Survey, Ireland

Engage

Early Engagement was key to understanding the requirements of the project. These requirements were not only technical but also social as the client required the survey to be carried out with the minimum impact and disruption to the public. The survey area included areas of significant environmental value and profile therefore minimum disruption and impact was key. With any large infrastructure project within an environmentally sensitive area the requirement to acquire geospatial data of private properties and lands is essential. To minimise the disruption to property owners and the public, these areas were surveyed using UAV technology. The client required the survey to be as unintrusive as possible so engagement at an early stage with the client’s liaison team was essential in agreeing the approach and methodology.

Plan

The project required the technical aspects of the project to be planned and executed in a particular sequence. The Primary and Secondary Control networks needed to be installed and coordinated prior to the topographical survey being carried out. IAA permissions were required for the UAV flight especially permissions to fly within some small aerodrome facilities along the route. The survey centred on the existing N11/M11 motorway which is a major commuter route for Dublin City. It bwas essential to the project that the motorway would be surveyed without disruption and inconvenience to the public.

Execute

The Primary control was installed along the route at 1km intervals and coordinated using a static GPS baseline network. The secondary control stations installed at 150m intervals along the regional and local roads were coordinated using high precision traversing and levelling techniques. The control and levelling networks were processed and adjusted using STARNET software since this is one of the most rigorous control processing and adjustment software packages available on the market.

The M11 motorway and most of the interchanges where surveyed using the mobile laser scanning platform. Control was installed at locations along the route and used to validate the accuracy of the colourised point cloud. The motorway and interchanges (64kms of carriageway) were surveyed in 2 days without the need for costly and disruptive traffic management. All public areas, and private areas to which we were granted access, were surveyed using a combination of total station, laser scanning and GPS techniques. Private areas which could not be accessed were surveyed using UAV technology. The survey data was processed using several processing packages including Autodesk Civil3D. Leica Geo Office and Trimble Business Centre. The UAV Survey was processed using Pix4D Mapper and Agisoft Metashape. The point cloud generated from the imagery was used to extract geospatial details which could not be accessed. This geospatial data was incorporated into the Civil3D model to provide an overall 3D Model of the survey area.

Deliver

The geospatial data was delivered in AutoCAD 3D DWG and GENIO formats. The aerial orthoimage was delivered in AutoCAD with ecw image files at a resolution of 50mm. The orthoimage could be loaded as a background to the AutoCAD DWG files.

During processing the data was checked using in-house developed scripts which check certain aspects of the data to ensure the quality of the data. The high resolution aerial orthoimagery was used to verify many topographical survey details such as road markings, street furniture and changes of surface. As an add-on to the project we delivered the LAS point cloud from the mobile laser scanning which the client found very useful when analysing bridge clearances along the route.

Review

The client carried out a robust quality control check on the delivered data for each zone and only after carrying out this process did the client approve the deliverables. One lesson learned on the project was that combining data from the different technology platforms must be done at the earliest possible stage of processing so the 3D model is processed as a single model.