Lidar Base Specification 2021 rev. A Now Available
Lidar Base Specification Online
The Lidar Base Specification (LBS) is the source of requirements for collections under the 3D Elevation Program (3DEP). The latest version of the specification is LBS 2024 rev. A, released in January 2024. See below for previous versions.
Lidar Base Specification Revision Status
The 3DEP Lidar Base Specification undergoes a continuous revision and update process. Revision requests are submitted through the 3DEP Working Group (WG) and the National Geospatial Technical Operations Center. Requests are reviewed by the Elevation Specifications Review Board (ESRB). If the ESRB approves a request, it is reviewed for final approval by the 3DEP WG.
Restrict use of the LAS Withheld bit flag
Use of the withheld bit flag is limited to identifying points that cannot be reasonably interpreted as valid surface returns. Current requirement is not clear on this limitation.
LAS withheld bit flag proof of performance
Proper use of the withheld bit flag is of significant importance in point cloud processing and the creation of derivative products such as a digital elevation model. This change requires proof of performance that the withheld bit flag was used properly. This change will be incorporated with "Restrict use of the LAS Withheld bit flag" revision and also includes the Maximum Surface Height
Lidar Base Specification Appendix 1: Maximum Surface Height Rasters
Lidar Base Specification 2024 rev. A
Requirements for the creation of Maximum Surface Height Rasters (MSHRs), the preferred proof of performance for withheld bit flag usage.
Lidar Mapping Report
USGS requires descriptive metadata to accompany 3DEP datasets. This documentation is intended to convey characteristics of the lidar mapping campaign as well as the data. This lidar mapping report guidance identifies key components of the data collection and processing that may be useful to USGS staff reviewing the data as well as data users.
Revise use of the Overlap Bit Flag
The current requirement regarding the usage of the overlap bit flag is vague and confusing, referring to the flag as "overage". The proposed revision is to end the usage of the overlap bit flag for 3DEP projects.
Checkpoints within DPA
All checkpoints are to be located within the DPA boundary. This is a requirement in the Collection Area specification section. It is being reiterated in the Checkpoint section of Data Processing and Handling.
Checkpoint Photographs Update
This change pertains to checkpoint photograph delivery requirement. The current requirement is for checkpoint photographs to be delivered embedded in a single PDF document. This modification allows for delivery as individual photographs in sub-directories to maintain image quality and allow for redaction of single images, if necessary.
Swath Separation Images Update
The requirements for Swath Separation Images (SSI) are being updated to allow only last returns, instead of all returns, in image creation. The resolution requirements are also being relaxed in order to provide more flexibility in SSI creation.
Elevation Specification Resources
A variety of resources supporting the acquisition, processing, validation, and publication of 3DEP elevation data are available through these Elevation Specification Resources pages. This includes Lidar Base Specification suporting and background information, the Lidar Error Dictionary, the Spatial Metadata Data Dictionary, and other explanatory information.
Lidar Error Dictionary
The purpose of this dictionary is to provide standardized language to describe commonly encountered errors associated with lidar datasets submitted to the USGS data validation unit for ingestion into the National Map. This document will improve communication between 3D Elevation Program operations personnel, the project’s point of contact, contributors, partners, and contractors.