True View for Construction Inspection
Author: Lewis Graham
Published On: August 06, 2020
The True View family of 3D Imaging Sensors (3DIS) are ideal for a very wide variety of tasks from visualization to detailed topographic mapping. Our customers are beginning to recognize that the difference between LIDAR data and true colorized LIDAR data is a real game changer.
Monitoring Construction Sites
We were recently mapping a construction site (actually our own new building) and realized the tremendous value of the True View 3DIS for monitoring construction sites. Now of course we know using drones for monitoring construction progress is nothing new. Many organizations are using camera-equipped drones to capture still and motion video. These data are very quick to collect and require no post-processing. For quick visualization, they are extremely efficient. The problem is they are qualitative only - you cannot make accurate measurements from the data.
Difficulties of Photogrammetry
An improvement on simply collecting visualization data is to employ photogrammetry. The images are processed in one of the common "point cloud from imagery" packages such as Metashape (Agisoft), ContextCapture (Bentley Systems Inc.) or Pix4D Mapper (Pix4D). While this forms a metric (measurable) base for quantitative analysis, there are still a few problems. The first is the difficulty photogrammetry has in capturing long, linear features such as poles and wires. The second is the inability to see stacked vertical features. You typically will find only a single vertical value for each X, Y location in the data set. But one of the biggest disadvantages of photogrammetry is the processing time. A simple 10 minute data collection flight will requires hours of processing time to generate a photogrammetric point cloud.
LIDAR + Imagery
The True View 3DIS, however, combines the best of both worlds. They have a laser system so features such as poles and wires are easily captured. Stacked features such as layers of structural steel are no problem - flight lines are simply planned to provide oblique views of the site. Thus, the point cloud from the LIDAR is comprehensive and very accurate. The dual True View oblique cameras capture not only RGB data for colorizing the LIDAR data but also serve as inspection images. Finally and perhaps equally important to the above is the very fast processing time. It take about 2/3 of the flight time to totally process a True View flight. Thus if a flight is 15 minutes, the processing time will be about 10 minutes - ingest of raw data to fully processed colorized point cloud and geocoded images.
An example of a 3DIS data set is shown in Figure 1. These data are crisp and very accurate. I can easily measure point-to-point and areas to confirm the "so-far" as-built is according to plan.
Figure 1 :Colorized LIDAR View of site
The camera data of a True View 3DIS is typically considered as the source for colorizing the point cloud and for generating a site ortho photo mosaic. However, these oblique images are extremely valuable for construction QC. An example True View image is shown in Figure 2.
Figure 2: Image of True View 410 LIDAR/Camera System
These images can be used to do a wide variety of QC tasks. Are the beams correctly painted, are all bolts in place, are tie wires in the correct location, ½? This is extremely valuable additional information of the site.
Soon to be released will be True View EVO Explorer. This viewer will allow a user to click on a LIDAR point or a 3D feature vertex and automatically display all True View images that "see" the selected location. This new tool will make inspection a much quicker and more detailed experience.
True View 3DIS Isn't Just for Mapping!
The message I will leave you with is this - a True View LIDAR/Camera (3DIS) system is not just for mapping. Once you begin using the system, you will be amazed at the applications that come to mind and that customers are willing to pay you to produce!