Surveyors Account for 900 Buildings in Two Weeks with LiDAR
Nine hundred buildings in two weeks. In biting cold. Grabbing data down to 5 centimeters or better. It would be a daunting task anywhere, but especially so in the harsh winter of China’s Jilin province.
In Changchun, Jilin’s capital and largest city, local authorities are responsible for maintaining and improving city structures. Part of the effort includes a long-term project to improve insulation, provide maintenance and improve the exterior appearance on a large block of buildings in one section of the city.
The city’s plan to repaint exterior surfaces called for detailed measurements of the building facades — accurate to 5 centimeters (2 inches) or better. In order to achieve that level of accuracy, the city called in Heilongjiang Star Survey and Mapping Technology Co. Ltd. (Star Survey) to collect the required information.
Speed in the Field
Field work began in December 2016, just as the harsh Jilin winter set in. The Heilongjiang surveyors were given barely two weeks to gather accurate data on all 900 buildings.
Faced with the tight schedule, Star Survey knew that standard surveying wasn’t fast enough to capture the needed data in the allotted time. Instead, the company turned to laser scanning for data acquisition.
Star Survey assigned three survey crews to the project, and equipped two crews with various scanners and one of the crews with a Trimble SX10 scanning total station. The SX10 combines an advanced robotic total station with precise, high-speed laser scanning. The instrument uses its built-in cameras to collect high-resolution images of the scene. It also enables the operator to “see” through the telescope via a rugged Trimble Tablet running Trimble Access software.
Over a 10-day period, the SX10 performed detailed scans on 80 buildings. By leveraging the instrument’s long range and wide scanning field, the two-person crew could usually capture an entire building façade from just one setup. The SX10 is specified to 350 meters (Kodak Grey). The variables of surface color, texture and inclination to the instrument line of sight combine with obstructions to affect performance of any LiDAR instrument. Because of this variability, manufacturers don’t make definitive statements of range. Users understand this and expect range to vary. When additional setups were needed, the crew used the SX10 precise surveying functions to tie setup points together. In addition to saving time in the field, their approach reduced the time and complexity for post processing.
A second two-person team was equipped with Trimble TX8 and TX5 laser scanners. In 10 days, they collected data on an additional 400 buildings. Like the SX10 crew, they delivered each day’s data to the office graphics team. A third crew made up of seven more people and three different scanners worked for 11 days to capture data on 420 buildings.
Integration Drives Office Efficiency
In the office, Star Survey technicians used Trimble software to process and manage the field measurements. Data from the SX10 was downloaded directly to Trimble Business Center software (TBC). Because the SX10 could capture complete data for each building the technicians did not need to stitch together multiple scans, which provided significant time savings in the office. They could quickly complete their checking and quality assurance.
“The quality and color from SX10 data was awesome,” one of Heilongjiang’s graphics specialists says. Using TBC, the technicians combined the SX10 scanning data for individual buildings into larger point clouds that included multiple buildings.
Star Survey used Trimble RealWorks software to download and process data from the Trimble TX5 and TX8 scanners. Technicians merged and cleaned multiple scanned datasets to produce large, coherent point clouds. They also used RealWorks to process the data from the other scanners used on the project. Once the processing and quality control was complete, the point clouds were transferred from TBC and RealWorks into AutoCAD as requested by Changchun city officials. The seamless transfer enabled the design and graphics team to complete their work efficiently and on time.
A Successful Outcome
Fast data collection and efficient processing enabled Star Survey to meet the city’s requirements and deliver accurate, comprehensive information. By merging point cloud data with on-scene photographs, the planners were able to visualize the buildings in detail.
According to Star Survey, the Trimble solutions enhance productivity both in the field and office. “They provided significant savings in time and personnel,” says Yunfeng Wang, Star survey crew. “We were able to separate field and office teams, and the SX10 can be easily set up and scan a building in a short period of time. Data acquisition is very easy for office processing and drafting.”