Thursday, August 29, 2019

The advancement of technical approaches to gathering field data has turned to LiDAR. 
This will be a brief discussion on how LiDAR has become a tool that the land surveyor 
is using more and more each day.
The main advantages behind today’s surveyors growing reliance upon LiDAR technology lie in the variety of methods one can acquire the data in the field. One method is to perform a Terrestrial Scanning, by setting up a 3D Terrestrial scanner. To acquire data from a terrestrial scanner, an instrument is normally mounted on a stationary tripod where data is collected from that position. Another popular LiDAR acquisition method is Mobile Scanning. Mobile scanning is done by two popular methods, mounting it on some type of vehicle, or via backpack carried by a field technician. Mobile LiDAR units are mounted on vehicles and driven along roadways to acquire mapping data or asset locations. These units can also be attached to a rail system and moved along a railroad to gather data. Mobile units can be attached to other vehicles such as ATV’s and driven along off-road type conditions. The Backpack Scanner is a newer version of the mobile system made light enough to be carried on the back of a field person. The backpack version is being used to acquire data in major cities or along walking trails. To cover large acquisition areas at one time, aerial methods using fixed wing aircraft and helicopters are used. The Unmanned Aerial Vehicle (UAV) is also now a popular aerial acquisition method for small to medium sites that are suitable for flying under current FAA regulations. Ground control is still needed with airborne LiDAR, but not as many points are required, and the majority of the time Photo Identifiable (PID) points are chosen to be located after the flight has occurred. The PID’s are identified in the LiDAR point cloud and are chosen in locations that are in a safer location for the field surveyor to collect.

Surveyor collecting points using a GPS receiver

While the versatility in LiDAR data acquisition methods exists, the processing of the acquired data is where the challenge lies. Point clouds gathered using LiDAR are sizeable, and the computing power required to process datasets in a timely manner can be costly. The collection method and the piece of equipment used will most likely dictate the program(s) needed to process the raw data. Depending on the client and their requested deliverable, it may require multiple programs to produce useable data. The factor that tends to be overlooked in processing data is having knowledgeable staff that understands and knows how to process all of this data into something that is advantageous for the client.
LiDAR Technician processing a point cloud
Given the complicated nature of point cloud processing, why is anyone using LiDAR based information? The reasons to use LiDAR far outweigh the stumbling blocks. AXIS can process this data quickly and easily, having experience with applying high-density LiDAR to design-scale base mapping projects since 2012. By using LiDAR, more comprehensive detail of the site is surveyed in a fraction of the time when compared to traditional, single-point survey methods. The result is accelerated schedules and reduced project costs. During the full-foliage season, airborne LiDAR is capable of mapping terrain in certain vegetated areas where traditional photogrammetric methods cannot; and in many areas where land surveying efforts would be greatly impeded or costly to collect to the same level of detail. So long as the composition and density of the vegetation canopy permit the penetration of light from above, a LiDAR pulse can reach the ground below. Farmland that contains row crops can be easily traversed, have points acquired and the ground can be mapped. Voids in the LiDAR caused by vegetation obstruction can be supplemented with conventional surveying methods, merged into the LiDAR point cloud data, to develop a comprehensive digital terrain model (DTM).
LiDAR Sensor mounted in a fixed wing aircraft
The possibilities of the uses for the point clouds gathered through LiDAR are growing as the technology becomes more widely used. Firms are creating 2D base maps generated from the point clouds. 3D modeling can be created from the point cloud that allows the client to spin and maneuver the product. This gives users the opportunity to see a project without leaving the office and thus being able to design a final product more efficiently and accurately. One of the more exciting applications is the ability to create a “fly” through image and product. These are especially helpful when working in and around pump stations and buildings that have a lot of existing pipes and infrastructure which may require modifications in a very tight area.

The client base that is currently using this type of data is growing each day. Civil engineers are using the information to design better site plans for commercial and private uses. Environmental engineers are using LiDAR to map forests, wildlife habitats and environmentally sensitive areas. Water and wastewater engineers have found multiple uses for LiDAR for base mapping and pump station redesign. Architects are using LiDAR to redesign the interior areas of commercial buildings and create virtual “walk-throughs” for the client to see before construction begins. In short, LiDAR is an invaluable tool that provides decision makers with more data in a shorter and more useable timeframe.

Author Info: Barry Gleissner, Director of Surveying and Mapping at AXIS GeoSpatial, LLC, has 40 years of experience in land surveying. An accomplished surveyor holding PLS licensure in Delaware and New Jersey, Gleissner currently serves on the board of the Delaware Association of Surveyors and has served two terms as president of the New Jersey Society of Professional Land Surveyors (NJSPLS), having recently received the NJSPLS 2018 Surveyor of the Year Award. Gleissner directs AXIS GeoSpatial’s day-to-day survey and map production operations.