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Revise use of the Overlap Bit Flag

By NGP Standards and Specifications

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.

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Status of this revision: Published in Lidar Base Specification 2021 rev. A

Current requirement in Lidar Base Specification 2020 rev. A, Data Processing and Handling: 

Use of the LAS Overage (Overlap) Bit Flag

  • If overage points must be excluded to produce a uniform DEM then those overage points shall be identified using the LAS overlap bit flag in all point cloud deliverables.  For more information on the difference between overlap and overage, refer to figures 4–5 and the “Glossary” section. Identification of overage points allows their simple exclusion from subsequent processes where the increased density and elevation variability they introduce is unwanted (that is, DEM generation).

 

Approved revision:

Use of the LAS Overage (Overlap) Bit Flag

Delete existing text and replace with:

  • The overlap flag shall not be used for lidar point clouds intended for inclusion in 3DEP data holdings 

To be added:

Bare-Earth Surface (Raster Digital Elevation Model)

  • All ground-classified points not flagged as withheld shall be used in the creation of the bare-earth DEM