It is important to understand the source of any elevation data you decide to use. Elevation data can be created in a variety of ways; from ground based land survey to remote sensing systems, with each source of data having their own unique opportunities and limitations.
In this article, we will be discussing one source of elevation data: airborne lidar. Specifically, point cloud data collected in-flight using lidar scanners mounted on aircraft. This mode of elevation data collection is becoming increasingly popular among government agencies for a variety of reasons. In particular, it is a cost effective way to collect high-resolution information about the earth’s surface over large geographic areas.
Before collecting airborne lidar data, an organization will determine which data specifications they require such as the non-vegetated vertical accuracy (NVA) or the laser pulse density. This allows an organization to control the quality of the end-product. Today, publicly available airborne lidar collected in Canada and the United States typically ranges in NVA from 5 cm to 30 cm.
After a lidar point cloud is collected, it is often referred to as “raw” data. The raw data is then cleaned-up and processed into a more useful product for end-users. This product is typically a “classified point cloud” in which each of the points is assigned a classification (ground, water, bridge, vegetation, etc.).
For an end-user, like an architect, engineer or designer, the classified point cloud is often the best, highest-resolution elevation data they will be able to find online.
The images below shows a classified point cloud sourced from the United States Geological Survey (LA Sabine River LiDAR, 2018), accessed through Equator. The image on the left shows all point cloud classifications and the image on the right shows ground only points. As you can see, in the image on the left, trees, hydro lines, and even cars are visible!