Revision History for TM11–B4 By Hans Karl Heidemann Lidar base specification version 1.0 ----------------------------------------------------- Posted online August 17, 2012 ----------------------------------------------------- Revised and posted online October 29, 2014, version 1.1 In text of the report, the author has detailed the changes from version 1.0 to 1.1: 1.For clarification, numerous sections of the specification have been editorially revised, and there has been minor reorganization of the document. 2. Glossary definitions have been updated to align with those in the new American Society for Photogrammetry and Remote Sensing (ASPRS) Positional Accuracy Standards for Digital Geospatial Data (American Society for Photogrammetry and Remote Sensing, 2014) and other industry publications, and several new definitions have been added. Notable among these are: •Bridge and culvert, •Vegetated (and nonvegetated) vertical accuracy, and •Percentile. 3. Coincident with this revision of the specification, ASPRS also developed its own Positional Accuracy Standards for Digital Geospatial Data (American Society for Photogrammetry and Remote Sensing, 2014). With regard to elevation data, the new standards redefine how elevation accuracy is described and reported, and although any accuracy could be its own accuracy “class,” a number of common classes are explicitly defined. The previous ASPRS vertical accuracy standard (American Society for Photogrammetry and Remote Sensing, 1990) was based on contour interval (usually expressed in feet [ft]), resulting in non-integer accuracy thresholds when converted to the metric units typically used with lidar (for example, 9.25 centimeters [cm]). The new ASPRS standard abandons the dependency on contour interval and is based entirely in metric units; its common classes are integer (for example, 10.0 cm). The NEEA QL definitions used common accuracy classes based on the earlier accuracy definitions and, to eliminate confusion about accuracy requirements as 3DEP moves forward, the QL accuracy definitions were adjusted to match the new ASPRS classes. Another quality level, QL0, was added as a placeholder for the higher quality data anticipated with future advances in lidar technology. The requirements stated for QL0 are somewhat arbitrary and are subject to change in future revisions of this specification. The changes relevant to lidar data QLs in this revision of the specification are as follows:QL0 was added with accuracy of 5.0 cm root mean square error in z (RMSEz) and density of 8 pulses per square meter (pls/m2). This accuracy aligns with the ASPRS 5-cm vertical accuracy class. •QL1 accuracy was changed from 9.25 cm RMSEz to 10.0 cm RMSEz. This accuracy does not correspond directly to any ASPRS accuracy class; it is a hybrid of QL2 accuracy and QL0 pulse density. •QL2 accuracy was changed from 9.25 cm RMSEz to 10.0 cm RMSEz. This accuracy aligns with the ASPRS 10-cm vertical accuracy class. •QL3 accuracy was changed from 18.5 cm RMSEz to 20.0 cm RMSEz and density was changed from 0.7 pls/m2 to 0.5 pls/m2. This accuracy aligns with the ASPRS 20-cm vertical accuracy class. 4. Also to align with the new ASPRS accuracy standards, accuracy is reported based on nonvegetated vertical accuracy (NVA) and vegetated vertical accuracy (VVA). These two classes replace the previously used fundamental, supplemental, and consolidated vertical accuracy (FVA, SVA, and CVA) classes. 5. The new ASPRS standards include recommendations tying the quantity of vertical accuracy check points required for a project to the areal extent of the project. Adherence to these recommendations is required by this specification. 6. QL2 has been established as the minimum required QL for new USGS–NGP lidar data collections. 7. Relative accuracy requirements for lidar data, within swath (intraswath) and between overlapping swaths (interswath) have been refined and established for each QL. A more detailed methodology for assessing and reporting these metrics is provided. 8. Lidar point data delivery is required in LAS v1.4 (American Society for Photogrammetry and Remote Sensing, 2011), Point Data Record Format 6, 7, 8, 9, or 10. Proper use of the Overlap and Withheld bit flags is required. 9. The block of lidar-specific metadata tags recommended in the previous version of this specification has been modified to reflect the other updates to the specification. The inclusion of this block is required in all lidar point data eXtensible Markup Language (XML) metadata files. 10. The 2 gigabyte (GB) limit on swath file size has been removed, although the method for splitting large swath files remains in the specification for use in situations where a data producer needs to produce smaller files. 11. The test area for assessing classification accuracy was changed from 1 kilometer square to 1 square kilometer. 12. Two additional point classification types are required: •Class 17, Bridges, and •Class 18, High Noise. 13.Anticipating that projects will more frequently use multiple coverage collection (for example, overlap greater than 50 percent) to achieve the higher required pulse density, terminology and requirements for this data organization have been added. 14.Requirements for datum and coordinate reference systems have been refined and clarified. Development and delivery of breaklines is required for all hydro-flattened water bodies, regardless of the methodology used by the data producer for hydro flattening. 15.Requirements and guidelines for flightline overlap and scan angle limits have been removed. Data producers are cautioned to be more rigorous about gaps in and the relative accuracy of the point cloud data. Lidar base specification version 1.0 (ver. 1.1, 2014) ----------------------------------------------------- Posted online October 29, 2014 ----------------------------------------------------- Revised and reposted November 13, 2014, version 1.2 The title was modified to omit “version 1.0” so version 1.1 and subsequent versions could be updated and confusion would be avoided with the most current version. Permission for this change was obtained by Ms. Sandra C. Cooper, BAO, by email October 30, 2014. --------------------------------------------------- Posted online November 13, 2014 --------------------------------------------------- Revised and reposted February 28, 2018, version 1.3 In text of the report, the author has detailed the changes from version 1.2 to 1.3: 1. The requirement for delivery of raw, unclassified swath data has been removed. 2. The requirement for XML metadata files for the overall project and for individual lifts has been removed. 3. A requirement to use Geoid12b to convert from ellipsoid heights to orthometric heights has superseded Geoid12a. 4. A requirement that specific coordinate reference system (CRS) information for all projects be agreed upon prior to collection has been added. 5. A requirement for vertical CRS information has been added. 6. A requirement to include the geoid model as part of the vertical CRS name has been added. 7. A requirement to represent horizontal and vertical CRS information as a compound CRS has been added. 8. A requirement that delivered raster elevation files must contain complete and correct georeference information for horizontal and vertical systems, including geoid model used, has been added. 9. A requirement for horizontal accuracy reporting has been added. 10. A requirement for delivery of ancillary products used to support processing of the lidar dataset has been added. 11. A requirement for an attributed polygon feature class representing individual swath boundaries has been added. 12. A clarification on the well-known text (WKT) representation of CRS has been added. 13. A clarification on intensity normalization has been added. 14. A clarification on handling of multiple CRS records in LAS files has been added. 15. A clarification on file source identifier (ID) for tiled LAS files has been added. 16. A clarification of the difference between overlap and overage has been added. 17. A clarification on the identification of overage (overlap) points has been added. 18. A clarification on requirements for the use of overlap and withheld point flags has been added. 19. A clarification on how model key points shall be identified using the LAS key point bit flag has been added. 20. The recommended process for assessing intraswath relative accuracy (repeatability, precision) has been refined to normalize for the natural slope. 21. The recommended process for assessing interswath relative accuracy has been limited to areas with less than (<) 10-degree slope. 22. The maximum limits for interswath differences have been removed. 23. A prohibition on duplication of points within a project has been added. 24. The classification code for “Ignored Ground” (typically used for breakline proximity) has been changed from 10 to 20 to correct the conflict with the ASPRS defined code for “Rail.” 25. A classification code for “Snow” (21) has been added. 26. A classification code for “Temporal Exclusion” (22) has been added. 27. Definitions of swath types have been added to the “Glossary” section. 28. Guidelines for breakline collection, compliant with a newly added EleHydro data dictionary have been added. 29. All references to the National Elevation Dataset (NED) have been changed to “the standard national DEM available through The National Map.” The names “National Elevation Dataset” and “NED” are no longer used for data collected and processed for The National Map or 3DEP. --------------------------------------------------- Posted online February 28, 2018 ---------------------------------------------------