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Clarify Intensity Requirement

By NGP Standards and Specifications

The current wording of the intensity requirement in the Lidar Base Specification is overly complex and attempts to limit processing by data producers. This revision will simplify the wording to better cite the ASPRS LAS specification. 

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Introduction

There are several individual requirements associated with intensity values in the Lidar Base Specification (LBS 2023 rev. A). Collectively, these requirements, which originated in very early versions of the LBS, attempt to expand on the ASPRS LAS specification. The current language in the LBS is difficult to interpret and is not consistent with standard lidar intensity processing. This modification will rely more directly upon the LAS specification language without further interpretation or restrictions.  

Current requirement: 

In LBS 2022 rev. A: Collection Requirements: Intensity Values:
  • Intensity values are required for each multiple discrete return.
  • The intensity values recorded in the LAS files shall be normalized to 16 bit, as required by the LAS specification version 1.4–R15 (ASPRS, 2011).
  • Intensity normalization shall be strictly linear.
  • Common image stretches (minimum-maximum, standard deviations, percent clip, histogram, and so forth) are expressly forbidden.
In LBS 2022 rev. A: Deliverables: Classified Point Data: 

  • Intensity values, normalized to 16-bit. See LAS specification version 1.4–R15 (ASPRS, 2011) for additional information. 

Change to: 

In Collection Requirements: Intensity Values:

  • Intensity values are required for each multiple discrete return. 

  • Intensity values recorded in the LAS files shall be linearly scaled to 16-bits per the ASPRS LAS specification version 1.4-R15 (ASPRS, 2011). 

In Deliverables: Classified Point Data: Reword the current requirement to read:  

  • Intensity values, linearly scaled to 16 bits. See LAS specification version 1.4–R15 (ASPRS, 2011) for additional information. 

Reference

American Society for Photogrammetry and Remote Sens­ing (ASPRS), 2011, LAS specification (ver. 1.4–R15, July 2019): Bethesda, Md., American Society for Photogram­metry and Remote Sensing, 27 p. [Also available at http://www.asprs.org/wp-content/uploads/2019/07/LAS_1_4_r15.pdf.]