O’Neil-Dunne: “What makes LiDAR special and what makes LiDAR unique from other types of overhead remote sensing?… Most of us are very familiar of course with aerial imagery, and with those photos that form the foundation of municipal GIS and mapping efforts. But LiDAR uses near infra-red energy… and that is a laser beam that you cannot see… It’s different because it’s not sensitive to things like shadows or lighting conditions, and LiDAr, unlike our imagery programs, can be flown at night.”
Light Detection and Ranging (LiDAR) is a type of overhead remote sensing in which a laser is pulsed to determine range and distance. While filling much the same niche as aerial imagery, LiDAR has a number of distinct use cases and advantages. These improvements allow for new applications, especially for local governments. LiDAR ignores shadow and light conditions, and can even be captured accurately at night. This increases detail over traditional imagery as well as allowing for new perspectives.
Additionally, LiDAR provides 3-dimensional information that aerial imagery cannot. This uniquely allows LiDAR imagery to be used as the foundation of 3-D GIS mapping. With the visualizations LiDAR makes possible, new applications are constantly being found. LiDAR has been implemented in a variety of use cases: mapping Line of Sight for traffic or security, accurately measuring erosion and elevation for flood modeling, and much more.
LiDAR is perfect for computer-aided feature extraction because of this increased accuracy. Tasks such as identifying building footprints are quicker with LiDAR than manual feature extraction. With the simplified interface of LiDAR, software can more easily interpret it than visual images, allowing for significant increases in automation. With LiDAR and increased GIS work hours can become vastly more efficient as a result.
How does LiDAR work?
O’Neil-Dunne: “LiDAR isn’t just those X, Y, and Z locations, those 3-D points, it also contains a wealth of information on things like the number returns. We’ve talked about before in the case of trees that the LiDAR laser itself will hit off the top of the trees and most times through. Here we’re symbolizing the LiDAR data looking at those multiple returns so things like the ground and the buildings generally appear blue, meaning they have lower returns, but the trees jump out here because they have multiple returns. So the takeaway message here is that there is a wealth of information sitting inside that LiDAR data set, inside that point cloud. It’s not just about elevation.”
LiDAR doesn’t just measure 3-D points, but also the number and variety of returns it receives from the laser. This allows it to clearly differentiate between different kinds of structures and patterns. Part of LiDAR’s improved accuracy is due to this ability to make detailed 3-D distinctions between objects. LiDAR also provides a large amount of information with each data point, allowing for a huge variety of applications.
However, this accuracy has a disadvantage of requiring increased processing power. One challenge to LiDAR is that there is so much data contained within it. This creates a greater demand on network infrastructure where LiDAR is being used and means that LiDAR files are larger than most aerial imagery. LiDAR compensates by providing more accurate and accessible information within each file. This means that each LiDAR file is through enough to cover a variety of different use cases and be turned into a number of different products; LiDAR can be used to map tree canopy, create Digital Service Models (DSM), and more.
How can you get LiDAR?
LiDAR can be found in a number of places online and may be purchased or created by a local, state, or federal agency. One great resource is the United States Interagency Elevation Inventory which provides LiDAR and other kinds of remote sensing for download for most of the country. There may also be more localized resources within each state such as the Vermont Center for Geographic Information, or the Massachusetts GIS (Bureau of Geographic Information). These state portals can provide additional services and resources for local users.
If you’re interested in purchasing LiDAR data of your own, AppGeo can help. With years of experience and intimate knowledge of the marketplace AppGeo can direct towards the ideal product and service for your LiDAR needs.
Continued reading: Canopy for Community – Urban Tree Canopy Mapping (Cincinnati, Ohio)