U.S. Army Corps of Engineers Sacramento District land surveying specialists are using modern technology fused together through some very creative “MacGyver-ing” to cut labor costs, improve data quality for numerous engineering disciplines, access otherwise impossible spots and keep surveyors safe from entering potentially dangerous locations.
You may be out of touch with modern surveying practice if your mental image is of two people on opposite sides of a field – one staring through a telescope (transit) and the second holding a colorful numbered rod (stadia).
While that standard surveying method remains a viable tool, Sacramento District engineering support personnel are exploring numerous fantastic possibilities in modern surveying tools that merge photogrammetry (measurements from photos); light detection and ranging (lidar); and on-site computer processing of multiple data streams to produce three-dimensional surface maps.
“The three-dimensional point clouds produced by this technology provides data and imagery that can be used by numerous Corps disciplines – civil, electrical, structural and mechanical engineering as well as archaeology and regulatory projects,” says David Mello, land surveyor with the Sacramento District’s engineering support group.
Sacramento District’s current MultiStation lidar units were purchased in 2016, replacing less-capable surveying equipment that had ended its service life. “It was an opportunity for our group to step forward and expand our capabilities,” says Mello.
These MultiStation units provide a variety of capabilities: robotic one-person surveying, imagery and terrestrial lidar. The lidar component can collect up to 1,000 points-per-second in a specific area selected by the surveyor and provide a 3D image model of the area or object. The same unit can also take photos of the same scanned area and later combine the photo with the lidar point cloud to create a colorized 3D image with very precise location data.
“It would require an incredible number of hours to produce this level of detail and spatial measurement by older surveying methods,” says Mello. “Many in our profession are now referring to this product as ‘reality modeling’ rather than just ‘terrain modeling’ because of the depth of information being gathered using this fusion of technologies.”
Multiple surveying trips to a single project site can be avoided, because a single lidar session can produce such a depth of information. Locations that are either totally inaccessible or extremely dangerous for traditional surveying teams can now be surveyed by some creative application of the new surveying technology.
Here’s a MacGyver case in point. The Sacramento surveying team wanted to produce a 3D image of a steep-sided canal that passes underneath an existing pipeline structure. To accomplish the task efficiently and safely, Mello’s team mounted a surveying prism; a sonar depth sounder; and a GoPro video camera aboard a radio-controlled boat that they piloted from onshore.
As the mobile sonar unit gathered underwater data, the lidar unit back on shore was collecting a data cloud image of the embankment topography and structures while also tracking the surveying prism on the boat for its exact location during each depth sounding.
The clever mashup of multiple technologies produced a 3D map of the drain structure, embankments and riprap walls of the canal; sonar measurements for the shape and depth of the canal profile; and video inspection of the canal walls.
“Because of the terrain, there was no practical way we could have used even a shallow-draft aluminum boat to enter the canal and gather that data,” says Mello. “And GPS tracking would have been impossible with overhead pipelines and heavy overhanging plant growth blocking GPS satellite signals.”
Such enhanced data-gathering capability means Sacramento District surveyors have a seat at the table very early in project formulation.
“At the start of any new project, our survey team examines the full scope and overall goals so we can make recommendations on what different types of data could be gathered,” says Mello. “This fusion of technology allows our surveying team to provide more data -- and more context for that data -- to every discipline involved in our Corps projects.”