Checking Accuracy Buried Fibre Lines

As-built plans are prepared and delivered by the contractor at the completion of the job. As built plans confirm the project as it has been actually built, showing any changes that were made from the planned and approved plans. SIEA checks the as-built plans to verify and assess their reliability. To accomplish this, SIEA personnel survey and record the actual position of the completed work to compare actual location and the submitted as-built plans. In the process, SIEA produces an accurate reference map for future maintenance and excavation accident prevention.

To start the verification, the as-built plans are downloaded into the EdiPocket software residing on the ProMark 500 rover's field terminal. The "Measure" menu has a function called "Accuracy Verification" that enables the operator to survey and record the position of the buried line at verification points as the operator follows the covered trench. According to Bruno Forget, SIEA GIS Department manager, most of the current checking is done on newly laid fibre-optic cables. A typical fibre-optic trench, filled in just after cable laying, is about 10 cm wide, which is more than adequate for accuracy verification. The positions are saved in a Shapefile then transferred to an Excel file, which makes the verification calculation and gives the result as-built plan "accepted" or "rejected."

SIEA uses the Ashtech ProMark 500 receiver, in L1/L2 GPS mode receiving real-time corrections from TERIA, the French GNSS reference station network, and a MobileMapper CX field terminal. The reliability and ease-of-use of the ProMark 500 rover makes it possible for virtually any operators to perform verification surveys with centimetre-level accuracy in real-time.

Bruno Forget adds that the ProMark 500 receiver with the software EdiPocket not only saves time for SIEA verification crews, but also increases the reliability and consistency of the entire geographic information system for SIEA.