The U.S. solar eclipse of 2017 appeared to have made just about everyone who owns a camera an “expert” in time lapse photography. Own a camera, you are a photographer, right? Not so fast; we see this all the time with scanner capture — own a scanner; you are a scan technician. Let me explain how a professional scan technician with a survey background is like the difference between a professional photographer and a point-and-shoot amateur.
LiDAR data can provide a wealth of detail with 2D camera integration. Fusion of LiDAR and camera data has many applications, such as virtual reality and autonomous driving, and can aid in data extraction. LiDAR scanners, like digital cameras, are line of sight. This is not X-ray technology. Features can be eclipsed, which is why project planning is vitally important. A land surveyor trained in spatial recognition understands line of sight for project planning to ensure maximum data collection. Understanding procedures like control, instrument calibration (the process of correcting the rigid body transformation between the LiDAR sensors’ coordinate system and the cameras) are all best practices of the land surveyor in everyday practice.
Camera lenses, which include the shutter and diaphragm, also must consider sun glare, camera angle resolution and field of view, as well as the overabundance of blue light due to atmospheric haze when addressing RGB colorized points. Aerial photographs are a perfect example of sizable angle distortion, known as oblique or high oblique images that can affect accurate topographic mapping, but can occur with both static and mobile use of cameras. Mobile LiDAR with georeferenced, time-stamped imaging is not self-contained. The scanners are calibrated the cameras are calibrated. Special software like TopoDOT, by Certainty 3D, integrated with the existing CAD capabilities of MicroStation, can unlock the visual full potential usefulness in data extraction.
The most important aspect a land surveyor adheres to is “honoring the point.” This means keeping the integrity of what is found in the field. In LiDAR terms, this means not warping the data to a known point. I have seen this warping done many times in LiDAR projects where it is then portrayed as zero error. But where is the truth now? This can affect camera mapping. An experienced land surveyor knows that all equipment contains error or an error budget. Mobile LiDAR systems with their global positioning stationing (GPS) and inertial measurement units (IMU) also have an error budget. Now add the tilt from focal length of digital camera lens or the relief displacement of an ortho photograph. A good example of this is using Google Earth to “measure distance” in an area of extreme vertical terrain differences. There is no accountability for the pitch of vertical elevation. The measurements can vary greatly. Control using feature extraction from digital imagery is also a concern for this very reason. This is why having the tools and understanding when mapping with digital imagery is vitally important.
Though many amateur photographers may have gotten some great images of the solar eclipse, I have to ask: What is their repeatability? How many images did not turn out before they got that one great shot? Thousands of images are taken on mobile projects. They all have to be useable. In the AEC world, a project will not wait another seven years for another opportunity to get it right. The LiDAR data and imagery has to be acquired right the first time.