Nine hundred buildings in two weeks — in biting cold — grabbing data down to 5 cm 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 to maintain and improve 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 façades — accurate to 5 cm (2 inches) or better. 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. In addition to conventional scanners, Star Survey put an important new technology to the test.
Star Survey assigned three survey crews to the project and equipped one of the crews with a Trimble SX10 scanning total station. The SX10 combines the functionality of advanced robotic total stations with precise, high-speed laser scanning. Used in conjunction with Trimble Access software, the instrument uses built-in cameras to collect high-resolution images of the scene and enables the operator to “see” through the telescope via a virtual display on a rugged tablet.
Over a 10-day period, the SX10 completed detailed scans on 80 buildings. By leveraging the instrument’s long range, the two-person crew could typically capture an entire building façade from just one setup. When additional setups were needed, the crew used the SX10 surveying functions to tie setup points together. In addition to saving time in the field, their approach reduced the time for office 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 comprising seven more people and three scanners worked for 11 days to capture data on 420 buildings.
Integration drives office efficiency
In the office, Star Survey technicians processed and analyzed the field measurements. Data from the SX10 was downloaded directly to Trimble Business Center software (TBC). Because the SX10 captured complete data for each building, technicians did not need to stitch together multiple scans and could quickly complete checking and quality assurance.
“The quality and color from SX10 data was excellent,” said one of Heilongjiang’s graphics specialists. 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 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. When 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 transfer enabled the design and graphics team to complete their work efficiently and on time.
A successful outcome
Star City’s performance kept the project on schedule. Fast data collection and efficient processing enabled technicians to meet the city’s requirements and deliver accurate, comprehensive information. By merging point cloud data with on-scene photographs, planners could visualize the buildings in detail.
According to Star Survey, the SX10 performed well and demonstrated the instrument’s flexibility. The solution provided “significant savings in time and personnel,” said Yunfeng Wang, survey crew leader for Star Survey. “We were able to separate field and office teams and the instrument can be easily setup and scan a building in a short period of time. Data acquisition is very easy for office processing and drafting.”
Based on its performance in such a demanding application, the SX10 has proven to be a valuable asset for Star Survey. In addition to scanning, the company will take advantage of the SX10 capabilities and use it on traditional work including cadastral surveys, topography, and building locations.
Erik Dahlberg is a writer specializing in the geomatics, civil engineering, and construction industries. Drawing on extensive training and industry experience, Dahlberg focuses on applications and innovation in equipment, software, and techniques.