# Toward a documentary standard for performance testing of terrestrial laser scanners used in forensic practice: A statistical procedure to assess change in instrument precision

## TL;DR

This paper introduces a statistical method to test if the precision of terrestrial laser scanners used in forensics has changed over time.

## Contribution

A new statistical procedure is proposed for assessing changes in TLS precision for forensic quality assurance.

## Key findings

- The proposed test procedure is illustrated using two examples of longitudinal TLS data.
- The method is designed to be inexpensive, concise, and flexible for use by forensic practitioners.
- The paper discusses the utility, scope, and limitations of the test in the context of instrument quality assurance.

## Abstract

This paper documents efforts by members of the Crime Scene Investigation and Reconstruction (CSIR) subcommittee within the Organization of Scientific Area Committees (OSAC) for Forensic Science, in collaboration with researchers at the National Institute of Standards and Technology, to develop a documentary standard for performance assessment testing of terrestrial laser scanners (TLSs). Intended to be performed by forensic practitioners, this “Interim Performance Assessment” is specifically designed to be inexpensive, concise, and flexible, and is comprised of two parts that separately evaluate instrument accuracy and precision. This paper motivates and details the second of these test procedures, which uses a statistical methodology to assess whether an instrument's point coordinate precision has significantly changed over time. In this paper, the statistical details are reviewed, and the proposed test procedure is illustrated through two examples of longitudinal TLS data. The utility, scope, and limitations of the proposed test procedure are discussed in the context of instrument quality assurance.