ISO 17123-3:2001

Overview

ISO 17123-3:2001 - Optics and optical instruments: Field procedures for testing geodetic and surveying instruments - Part 3: Theodolites - specifies field methods for determining and evaluating the precision (repeatability) of theodolites and their ancillary equipment in building and surveying measurements. The standard provides in situ, practical test procedures (without special ancillary equipment) designed to minimize atmospheric influences and to verify whether a particular instrument is suitable for the immediate measuring task. These procedures are intended as field verifications, not comprehensive acceptance tests.

Key Topics

• Purpose: Estimate repeatability (precision) of horizontal directions (HZ) and vertical angles (V) observed in both face positions of the telescope.
• Two procedures:
  • Simplified test procedure - single series (m = 1); uses 4 targets; limited measurements for a quick check against permitted deviations (ISO 4463-1). Indicative only; no formal statistical tests recommended.
  • Full test procedure - multiple series (m = 4); uses 5 targets; rigorous least-squares evaluation and statistical tests to determine experimental standard deviation and compare it to theoretical precision.
• Measurement geometry: Targets placed approximately in same horizontal plane, typically 100 m to 250 m away, evenly spaced around the horizon; targets should be unmistakable (target plates preferred).
• Measurement sets: Each series comprises n = 3 sets of observations; directions observed in face position I (clockwise) and II (anticlockwise); graduated circle rotated between sets.
• Precision metric: Experimental standard deviation (root mean square error) of a direction/angle observed once in both face positions. Full procedure includes statistical tests to assess population membership of measured variance and index error stability.
• Practical constraints: Procedures minimize atmospheric gradients and do not require laboratory conditions. Centreing accuracy guidance provided (e.g., plumb bob 1–2 mm; optical/laser plummet ~0.5 mm; centring rod ~1 mm).

Applications

• Field verification of theodolite suitability before construction layout and surveying tasks
• On-site quality assurance and repeatability checks by survey teams and geomatics engineers
• Routine field calibration checks by instrument technicians and contractors
• Input into measurement uncertainty assessments (as one component of the overall uncertainty budget, alongside reproducibility and traceability per the GUM)

Related Standards

• ISO 17123-1 (Theory) and other parts of ISO 17123 (Levels, EDM, tacheometers, etc.)
• ISO 4463-1 (measurement planning and acceptance criteria)
• GUM (Guide to the expression of uncertainty in measurement)
• VIM and ISO 3534-1 for statistical vocabulary

Keywords: ISO 17123-3, theodolites, field procedures, testing geodetic and surveying instruments, precision, repeatability, experimental standard deviation, horizontal directions, vertical angles, in situ testing.