The distance of the GNSS base station(s) to the LiDAR system during acquisition has a major effect on final accuracy. Second, these accuracy specifications are usually quite conservative. The processing of the point cloud can also contribute significantly to the achievable accuracy. Further, project deliverables are usually delivered with “absolute” vertical accuracies that meet certain ASPRS or NSSDA thresholds. Other sources of error like those introduced by the GNSS or inertial systems are far more important and are often the largest contributors to vertical error.Aerial Services is a Veteran Owned Small Business.A client told me the other day that some vendors are promising vertical accuracy of LiDAR deliverables that exceed the LiDAR manufacturer specifications for that system and asked: Is it legitimate for a service provider to promise better accuracy than manufacturer specifications? For the LiDAR-IMU calibration problem, it should be noted that the individual points in a LiDAR scan are sampled at … Those portions of the cloud obscured by vegetation and other objects are required to meet less stringent accuracies (“supplemental accuracy”). For these reasons there is no way to really know how accurate the deliverable is unless resources are spent that are necessary to statistically measure (estimate) its accuracy in the different point classifications. Riegl’s spec sheet for the system says that the accuracy for the system is 2.5 cm (1 sigma at 150m above ground). that when integrated, calibrated, and operated together all contribute error to the ultimate accuracy of the point cloud. For many projects, only a small portion of the project area may be modeled by “bare earth” classifications. Whether the data is aligned after flight to minimize IMU errors contributes to total error.
6315 Chancellor Dr. Cedar Falls, IA 50613The final accuracy of a point cloud (or the bare earth elevation model derived from the point cloud) is a product of the LiDAR “system” and a “production process”, and not simply the ranging from the laser. Quality stationary scanners boast survey-grade lasers and signal processing to produce millimeter accuracy. Fortunately, there are now commercial applications that enable sound statistical sampling and objective error assessment of point clouds (see Spatial Information Solutions TopoAnalyst) and do not rely on outdated manual or visual-only assessment methods.The short answer is “Yes”, it is possible to exceed these specifications, and “No” service providers may not be overselling their services by promising such accuracies. Depending on the intended use of the data, it is often advisable to verify the accuracy of the deliverables to specific standards.LiDAR is an extremely important tool in the hand of qualified professionals that is capable of providing a wealth of amazing and highly accurate geospatial information useful for engineering and land use planning. So let me try to put a little context on this complex concept.Further, this Riegl specification is expressed for a point cloud acquired at an unusually low altitude (150 meters above ground). The coating also introduces another angle error in addition to the glass.