NGP Standards and Specifications

Revise use of the LAS Withheld Bit Flag

Current wording of requirement is too broad and lacks clarity regarding which points must be flagged and how the bit flag relates to other classifications.

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Please note: this revision was modified on July 31, 2020 to remove a previous modification.  

Status of this revision: Provisional. This revision has been approved and will be included in the next release of the Lidar Base Specification.

Current requirement in LBS v.2.1:

Use of the LAS Withheld Bit Flag
Outliers, blunders, geometrically unreliable points near the extreme edge of the swath, and any other points the data producer deems unusable are to be identified using the withheld bit flag, as defined in LAS specification version 1.4–R13 (ASPRS, 2011).

ESRB-approved revision:

Use of the LAS Withheld Bit Flag
  • The withheld bit flag, as defined in LAS specification version 1.4–R15 (ASPRS, 2011), shall be used to identify points that cannot be reasonably interpreted as valid surface returns. Examples include outliers, blunders, geometrically unreliable points, aerosol back-scatter, laser multi-path, airborne objects, and sensor anomalies.
  • The withheld flag may be used in conjunction with other classification codes (low/high noise for example), but it should be used in all cases where the previously mentioned criteria are met.