Virtual design and construction teams are quickly discovering the value that drone mapping brings to all stages of a construction project, including initial site survey and design, volume and elevation measurements and comparisons, and quality assurance. In a fraction of the time it takes to conduct a ground-based survey, a drone can automatically fly and capture imagery of a project site that can then be processed into highly-accurate point clouds compatible with Building Information Modeling (BIM) software.
The VDC team at Brasfield & Gorrie, one of the largest privately-held construction firms in the United States, is setting the standard for the use of drone mapping in construction. Brasfield & Gorrie has equipped each of their regional offices with DJI Inspire series drones and their 24-person VDC team has incorporated drone mapping into their everyday business practices.
Survey-Grade Models Produced in a Fraction of the Time
Using traditional ground methods, a 60-acre site could easily take two or even three weeks to survey. For Brasfield & Gorrie’s VDC team, drone mapping reduces that process to four days or less from initial request to importing the point cloud to BIM software. Some of the biggest time savings come from the data collection step. For most construction sites, it takes less than an hour to fly and capture mapping imagery. Then, just upload the flight photos to the cloud-based DroneDeploy platform and wait for them to be processed into a map and 3D model — without taxing your own servers.
And project managers don’t need to sacrifice accuracy either. By using ground control points (GCPs), DroneDeploy customers can achieve centimeter-level accuracy. Once the 3D model is complete, DroneDeploy allows VDC teams to export point clouds into local coordinate systems by simply entering a 4-digit EPSG code. The result: survey-grade data in a fraction of the time compared to traditional ground survey methods.
“We saw what was a 2–3 week and several tens of thousands of dollars process become a 1–4 day process with only a couple thousands of dollars invested in equipment and software,” says Cole. “When you’re looking at a dramatic 75% or greater cost and time improvement — it’s really powerful.”
High-Resolution 3D Models Revolutionize the Work of VDC Teams
Not only are drone-based surveys faster to perform than ground-based surveys, but they also deliver much more detailed data. A traditional survey may only yield a few hundred points of resolution, whereas drone-generated point clouds can contain millions of points. The result is a high-resolution 3D model that is revolutionizing the work of VDC teams and the project and site managers they work with. Cole noticed the extent of this when he analyzed a 3D model of one of Brasfield & Gorrie’s sites.
High-resolution point cloud
The 3D point cloud was so detailed that he could see each powerline over the site and each individual stud in the multifamily apartment complex under construction. In fact, the point clouds his team produces are so detailed, that when he showed one to a colleague recently, it was mistaken for a video.
“I said no, no, this is actually a 3D point cloud, and I can get the volume of any material stockpile on that site, I can make any linear measurement — so this is a really detailed point cloud that showcases the quality of data you can get.” — Hunter Cole
Integrating Drone Point Clouds in BIM Enables Powerful Analysis
A completed drone-generated point cloud is just the beginning. The real power comes once that model is integrated into BIM software. The Brasfield & Gorrie team generates point clouds in DroneDeploy and then imports data into Autodesk Revit, where they overlay it with the 3D site plan models and other data to improve processes such as:
- initial site survey and design
- quality assurance- comparing actual construction against plans
- measuring and comparing changes over time
The Autodesk app within the DroneDeploy interface makes it easy to send point clouds directly to your Autodesk Forge account.
Below are a few examples of how Brasfield & Gorrie is leverages point cloud data in BIM software to make better decisions.
For this tower construction project, the VDC team overlaid the architect’s design for the project as well as crane clearances onto a 3D point cloud of the existing site to confirm and optimize where to place the cranes during the construction process.
Fly-through of the combined point cloud, design
Heat map comparing earthwork to site plans. Green indicates elevations match design plans, blue indicates elevations too low, red indicates elevations too high
During construction of a 61-acre hospital site in Florida, the Brasfield & Gorrie team used a drone-generated 3D point cloud to help a site manager compare a subcontractor’s initial earthwork with site plans. Because the site manager was concerned that the subcontractor had not exported enough soil, accuracy and timeliness were key.
Verifying Concrete and Pipe Work
The final output was a heat map showing the external contractor’s earthwork progress compared to the initial plans, and the site manager was able to conclude that the subcontractor did need to export more soils to reach the correct elevations.
VDC teams can even overlay existing design models on top of drone-generated point clouds depicting site conditions.
In this example, Brasfield & Gorrie overlaid the design model for this processing plant on top of the 3D model of the site conditions to verify that concrete footings and pipes had been put in the right place.
“I can overlay a point cloud over that 3D model, line it up exactly and see, for the first time, what’s been built versus the design intent,” says VDC Coordinator Hunter Cole.
From site planning, progress monitoring and verification of contractor work, drones are increasingly being using in many areas of the construction site. With the ability to get on site and deploy drones or uavs quickly and efficiently, take images, and process into accurate 3D models and point clouds creates a huge opportunity for efficiency and time savings.
If you would like to understand more about the techniques used in this blog download the case study on Brasfield & Gorrie that deep dives into the way they used drone generated 3D point clouds to accurately compare actual earthwork to site plans.