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Restrict use of the LAS Withheld bit flag

By NGP Standards and Specifications

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. 

 

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

Requirement in Lidar Base Specification 2020 rev. A:

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.

Published revision with "only" added (addition is bolded):

Use of the LAS Withheld Bit Flag
  • The withheld bit flag, as defined in LAS specification version 1.4–R15 (ASPRS, 2011), shall only 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.