“The combination of a drone and photogrammetric software made it possible to complete all of these projects with much higher levels of safety, cost efficiency and accuracy than could have been achieved with conventional techniques”
“It is very difficult to take measurements that high and to find safe and appropriate total station setups while surveying by the highway,” Lepine said.
Several years ago, exp began using PhotoModeler photogrammetry software from Eos Systems. exp originally used a different software package but switched to PhotoModeler when it was discovered that PhotoModeler could be purchased for the amount that it cost to rent the other software for one month. When Lepine first began using photogrammetry, he placed photo control targets on the rock and surveyed the 3D coordinates for those points in order to provide the proper scale rotation and translation for the photographs. He then walked along the rock slope and took pictures with a digital camera, taking care to obtain at least a 60% overlap between adjacent pictures. This process took only one day for a 100 meter long rock slope.
When Lepine returns to the office, he uploads the photos into the photogrammetry software and uses a feature called SmartMatch to automatically detect and match features across multiple overlapping photos. The software then computes the position of each point in the images in 3D space. “SmartMatch saves a considerable amount of time compared to the previous process of manually matching common features between the photos,” Lepine said. “The time required to orient the photos is reduced from a few days to a few hours. The result is a dense point cloud consisting of millions of points that defines the topography of the rock slope to a much higher level of accuracy than was possible in the past.” Accurately depicting the 3D geometry of the rock slope is critical because contractors prepare their bids for the remediation work based on this geometry.
More recently, exp has further improved the survey process by using a DJI S900 Hexacopter UAS with a calibrated Sony NX5T camera to take the photos. Lepine commands the UAS to hover and moves the gimbal into position for the shot of the rock slope.