The popularity of mobile laser scanning is on the rise in the surveying world, as are expectations for survey grade accuracy. LiDAR systems have now reached a size where they are not only easily portable but also able to provide greater levels of accuracy than previously possible.
The collection of field data has previously relied on repeated set-ups of a traditional terrestrial laser scanner but mobile scanners now allow surveyors the opportunity to collect data rapidly and remotely using either wearable units or systems such as ROBIN which can also be mounted on to a road vehicle, helicopter and UAV.
As part of our development process we often look to challenge ourselves and our technology, so for a recent demonstration, we decided to see how quickly we could scan the Silver Jubilee Bridge in Runcorn and get the data processed using ROBIN, our latest mobile LiDAR system.
Generally speaking, FOG IMUs have better accuracy than traditional MEMs (Micro Electromechanical System). In particular attitude accuracy is higher and gyro random walk (gyro-rw) is less which leads to reduced drift when there is no satellite coverage.
Completed in 1961, the Silver Jubilee Bridge has an elevation of 87 metres over the River Mersey and is constructed out of 6000 tons of steel. At nearly 500m long, it remains one of Europe’s longest steel arch bridges. The bridge had previously been surveyed using a total station by one of our civil engineering clients so control points could be used to measure the success and accuracy of the trial.
ROBIN has a relative accuracy of around 10-20mm but often, when dealing with complex structures such as this, engineers and surveyors prefer to collect the most accurate data-set possible, so our chief engineer Dr Chris Cox decided to test the powers of our most accurate mobile system yet – ROBIN +PRECISION.
ROBIN +PRECISION represents the latest in technological innovation for situations where absolute accuracy is important or applications where GNSS is limited. High accuracy applications include highway surveying and monitoring of critical infrastructure such as rail networks. With a survey grade fibre optic gyro (FOG) IMU, ROBIN +PRECISION can be used on projects where there is little or no GNSS, such as urban mapping, tunnel surveying and forest mapping.
ROBIN’s unique mounting system means that the pod can be attached to either the included backpack or vehicle mount and weighing in at only 9KG, a scan can easily be set up and performed by a solo operator.
Chris got the system attached to the 3DLM truck and calibrated in under ten minutes and set off. With only 4 passes needed (two per lane), a detailed scan was performed in around 30 minutes, including the roads at either end of the site, capturing data at over a million points per second. Back in the office, Chris set about processing the data using the bundled software package, MMProcess. In a little under 3 hours, we had a full dataset and pointcloud of the Silver Jubilee Bridge, demonstrating the accuracy of ROBIN +PRECISION to 7mm.
The scan data was compared to control points provided by the client. The control points were placed on the ends of the white painted lines on the bridge carriageway, which were surveyed in and levelled using total stations. When compared to the scan data the resulting RMS in elevation was 7mm and a standard deviation of 7mm.
The numerous overhead sections of steelwork on the bridge presented GNSS difficulties, but the survey-grade IMU used on the ROBIN Precision kept the IMU drift to a minimum allowing the system to achieve a very high level of accuracy. The standard model ROBIN may have had slightly larger drift, potentially decreasing the absolute accuracy to over 15mm.
Upon identifying a gap in the market, ROBIN was designed to meet the ever increasing needs and demands of field-based survey teams who not only require the latest in technological innovation but also need to prove a tangible return on investment. ROBIN is currently the only system available which has the ability to be mounted on to different vehicles, including airborne units, as well as be used in difficult to reach locations on foot. Extra upgrades and integrations, such as +SLAM also mean that any investment made is future-proof, making one system suitable for a range of additional applications.
Watch the Point Cloud Animation
Any application where absolute accuracy is important or applications where GNSS is limited. So for example, high accuracy applications include highway surveying and monitoring. Applications with poor GNSS include urban mapping, tunnel surveying, forest mapping.
Generally speaking, fibre optic gyro (FOG) IMUs have better accuracy than MEMs, in particular attitude accuracy is higher and gyro random walk (gyro-rw) is less which leads to reduced drift when there is no GNSS (i.e. absolute accuracy of a FOG IMU will be better than a MEMS IMU when there is little or no GNSS).