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Revise use of the LAS Withheld Bit Flag

By NGP Standards and Specifications

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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Status of this revision: Published in Lidar Base Specification 2020 rev. A

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).

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.