Traceability of surveying and geadetic instruments

Project Description

It is clear that all kind of measurements should be traced to their based basic units. Traditionnally, geodetic and surveying instruments have been formally out of the traceability chain, in spite of instruments used on this field (EDMs, theodolites, ...) measure length, angle or both. This may be due to the fact that this kind of instruments had resolutions and precisions worst (altgough appropriate to the needs) than other instruments used in closed laboratories. With the increasing of precision also in this field, due to new developments, the application of new techniques, and the arrival of quality systems, distributors of this kind of instruments should demonstrate to their customers the traceability chain linking the instruments they sell and repair to the standards maintained by their mother companies and also to the national institutes where these companies are located.

The situation is not clear because due to long ranges of measurements of these instruments is not easy to find standards (étalons) and calibration procedures to be applied within metrology laboratories. It is also difficult to find all over Europe accredited laboratories working in this range of instruments.

The purpose of this project is to collect the best possible updated information about this kind of instruments (EDMs, theodolites and others):

• How are they linked to national standards in each country?
• Are there accredited laboratories in this field?
• What kind of standards and calibration procedures are used by the national labs. Or equivalent institutions?
• Information about calibration and accreditation processes when the national labs. has no activity in this field
• Any other information valid for knowing much more about the general situation in Europe

Final Report 2002-09-05

With the purpose of collecting the best possible updated information about this kind of instruments (EDMs, theodolites and others), a specific questionnaire was sent to all NMIs, containing the following questions:
1.0 Do you calibrate any of the following list of topographic/geodetic instruments? If not, which Institution in your country does it make this type of calibrations? How do they get traceability?
1.1 Please, explain briefly the method you use for calibrating: theodolites, opto-mechanical levels, laser-beam levels, leveling/encoded scales/rods, EDMs, tachymeters, GPS, others.
1.2 Do you calibrate photo/video-grametric instruments? Please, explain how. If not, which Institution in your country does it make this type of calibrations? How do they get traceability?
1.3 Do you realize any calibration using photo/video-grametric techniques? Please, explain. If not, which Institution in your country does it make this type of calibrations? How do they get traceability?
1.4 Do you realise any calibration in which you have to determine 3-D objects using topographic methods? Please,explain. If not, which Institution in your country does it make this type of calibrations? How do they get traceability?
1.5 Do you evaluate the measurement quality of topographic systems used in metrology? Please, explain. If not, which Institution in your country does it make this? How do they get traceability?
1.6 In your country, is there any national or international written standard being applied to these topographic instruments? Please, indicate.
1.7 What kind of (materialised) standards do you use for realizing each one of the calibrations you do?
1.8 What is the best uncertainty you claim for the different type of calibrations you realise?
1.9 Which standard, instrument or measuring system do you consider “suitable” for establishing comparison campaigns?
2.0 Please, indicate selected bibliography (in a wide sens) you consider “compulsory to read” in this field. There were received 14 answers, showing 8 NMIs plus 12 other Institutions offering calibrations on this field.

CONCLUSIONS:

• In most of cases, there is traceability to NMIs through materialized standards.
• Sets of collimators, invar rods, rotary tables, benches, laser interferometers and baselines are the main means/standards used for calibrating such instruments
• Only three Institutions (none NMI) use and calibrate fotogrametric and videogrametric instruments
• Very few (practically none) calibrations of 3-D objects using topographic methods. Laser tracker systems are used more and more
• Nobody evaluate the quality of topographic systems used in metrology
• There are written standards: ISO 8322-1 to -10 and DIN series applied in this field. These are “field” standards more than “laboratory” ones. So, they are more related to precision (repeatability) than to accuracy (trueness), using different language: standard deviations and maximum permitted errors instead of uncertainties.
• Claimed uncertainties are comparable among them and according to needs. There are some difficulties for calibrating long range EDMs and GPS.
• As standards suitable for comparison campaigns EDMs and theodolites are mainly mentioned as travelling ones.

FINAL NOTE: An extensive report containing the summary of all NMIs’ answers has been produced. It will be posted in the Length Web site (www.npl.co.uk/euromet/length), open for further additions along the time.