Project Specifications

Numerous sensor parameters affect the desired quality and specifications of the LiDAR data. The USGS LiDAR Base Specification Version 1.2 provides three of the most common LiDAR Quality Level (QL) specifications relevant to industry QL1 LiDAR (with 1-foot contour accuracy and 8 points/m2), and QL2 LiDAR (also with 1-foot contour accuracy but with 2 points/m2) both ensure that the point cloud and derived data products are suitable for the inter-Agency National 3D Elevation Program (3DEP); whereas QL3 LiDAR (with 2-foot contour accuracy and 0.5 point/m2) ensures that the bare-earth DEMs derived from LiDAR data are suitable for ingestion into the National Elevation Dataset (NED). Using the USGS Lidar Base Specification at any of these three Quality Levels will ensure that it is consistent with the goals of the National Digital Elevation Program (NDEP). Also see the ASPRS Positional Accuracy Standards for Digital Geospatial Data, at Appendix D, from which the Elevation Data Vertical Accuracy Standards were extracted in Chapter 3, Table 3-6. LiDAR point density and vertical accuracy are the two main cost drivers of an airborne LiDAR survey. LiDAR data can be collected with a wide variety of point densities depending on the needs of the project. The selection of point density is a big driver of the overall cost of a LiDAR project and should be selected with consideration to the end uses for the LiDAR. A LiDAR product with 1 point per square meter (ppsm) is sufficient for many applications such as flood mapping in many areas. Higher point densities (4-8 ppsm) allow for greater utilization of the data for mapping planimetric features such as roads and structures as well as for vegetation analysis such as biomass and canopy studies. Additionally, specialized LiDAR at very high densities > 20 ppsm are often used for mapping infrastructure in greater detail such as power lines, pipelines, and for significant features such as mile posts and signs. The ground conditions should be considered when selecting a point density as well. If the area is covered with dense vegetations such as a coniferous forest a higher density and more overlap would be required to penetrate to the ground than an area where leaf-off conditions exist.

1. Geographic area to be mapped (normally based on government-provided shapefiles);
2. Returns per pulse (typically is 3 or more including, first, last, and intermediate returns);
3. Collection conditions (e.g., ground is snow free, vegetation is leaf-off);
4. Ground control and/or direct georeferencing requirements (airborne GPS and IMUpositioning and orientation), if any;
5. GPS base station limitations, if any;
6. Data void guidance, if any (void areas are allowed over open water and typically wet orvery new asphalt);
7. Vertical accuracy (using current ASPRS and NDEP methods where NVA is tested asAccuracyz (RMSEz x 1.9600) and VVA is tested using the 95th percentile); NVA and VVA definitions are provided in Chapter 3 of this manual;
8. Horizontal accuracy (normally compiled to meet a specified value rather than tested tomeet a specified accuracy value);
9. Relative accuracy (threshold, typically stated in terms of RMSE, of vertical offsetbetween adjacent flight lines);
10. GPS-IMU trajectory solutions should be delivered and assessed for combined verticalseparation between the forward and reverse trajectory solutions;
11. Tiling schema including size of final tiles and naming convention (e.g., 1,000 meter gridwith no over-edge named according to the U.S. National Grid);
12. Horizontal datum (e.g., North American Datum of 1983 (NAD83)/2011 adjustment);
13. Vertical datum (e.g., North American Vertical Datum of 1988 (NAVD88), using the mostrecent National Geodetic Survey (NGS)-approved GEOID model for conversions from ellipsoid heights to orthometric heights, currently GEOID12A;
14. Coordinate system (e.g., UTM or State Plane Coordinate System);
15. Vertical and horizontal units (e.g., meters, or U.S. Survey Feet) – note, never specify “feet” but instead specify U.S. Survey Feet or International Feet;
16. What classes are required (e.g. 1-unclassified, 2-ground, 7-noise, 8-model key points, 9-water, 12-overlap, etc) (See section 1-4.c. for a description of classifications);
17. Processing requirements (e.g., percentage of elevated features allowed to remain in the ground classification, guidelines for over-smoothing/inconsistent editing, thresholds for artifacts/spikes/divots/cornrows, uniformity of point distribution);
18. File format (industry standard is LAS format following ASPRS formatting guidelines and specifications);
19. Compression (e.g., are compressed files allowed, if they are to be delivered in addition to or in replacement of non-compressed files, and what format should be used for the compressed files);
20. Ff intensity imagery is required, specify the resolution or pixel size;
21. If breaklines are to be collected, specify types of breaklines, minimum size for collection,monotonicity/connectivity requirements or topology rules that must be followed, and desired final format of the breaklines (e.g. ESRI shapefile, ESRI geodatabase, DXF, DGN, etc.);
22. If DEMs (such as bare-earth DEMs or first return DSMs) are to be created, specify thepixel resolution, hydro-flattening or hydro-enforcement requirements, and final format (ESRI Grid, IMG, GeoTIFF, etc.);
23. If contours are to be created, specify the interval, coding (intermediate, index, etc), levelof smoothing to be applied (e.g. engineering grade, moderately smooth, cartographic grade), and the desired final format (e.g. ESRI shapefile, ESRI geodatabase, tiled, non-tiled);
24. Metadata requirements such as those defined in the IAW geospatial manual;
25. QA/QC procedures;
26. Reports to be submitted (e.g., survey report with field work procedures, data acquisition
    report, calibration procedures, production report, QA/QC report); and
27. Deliverables and due dates.

Please note, however, that industry managers should make every effort to utilize existing ASPRS standards and specifications listed above to ensure that the data will be interoperable, usable and available to others.