A LiDAR point cloud often is described by its Quality Level (QL), which is comprised of the nominal pulse spacing / density (NPS / NPD) and the relative and absolute vertical accuracy of the point cloud and derived digital elevation models. NPS and NPD refer to the point density of single swath, single instrument, first-return-only data. The aggregate nominal pulse spacing / density (ANPS / ANPD) describes the net overall pulse spacing and density including overlapping swaths and multiple passes of the LiDAR system.
Table 1 and Table 2 (from the USGS LiDAR Base Specification v1.3) describe LiDAR Quality Levels with regard to ANPS / ANPD, relative accuracy, and absolute accuracy.
Table 1
Aggregate Nominal Pulse Spacing and Density
Spacing (m)
Density (pls/m2)
QL quality level pls/m2 pulses per square meter m meter ≤ less than or equal to ≥ greater than or equal to
Table 2
Relative Vertical Accuracy for LiDAR Swath Data
Repeatability, RMSD, (m)
Difference, RMSD, (m)
QL quality level pls/m2 pulses per square meter m meter ≤ less than or equal to ≥ greater than or equal to
Table 3 and Table 4 describe land cover classes used for reporting absolute accuracy of the LiDAR point cloud.
Table 3
Land Cover Classes
FVA Fundamental Vertical Accuracy SVA Supplemental Vertical accuracy NVA Nonvegetated Vertical Accuracy VVA vegetated vertical accuracy n/a not
applicable or not available
Table 4
Absolute Vertical Accuracy for LiDAR Data and Digital Elevation Models
QL quality level RMSE root mean square error in the z direction NVA non-vegetated vertical accuracy VVA vegetated vertical accuracy m meter ≤ less than or equal to
Table 5 Describes the minimum classification of the LiDAR point cloud for the USGS 3D Elevation Program. Table 6 Describes the requirements for the minimum cell size for the digital elevation models that are derived from the bare-earth classified point cloud.
Table 5
Minimum LiDAR Data Classification Scheme
Table 6
Minimum Digital Elevation Model Cell Size
QL quality level m meter ft feet