METROLOGY NORWAY SYSTEM - AN ON-LINE INDUSTRIAL 
PHOTOGRAMMETRY SYSTEM 
Alf Pettersen, Tech. Mgr., Metronor AS 
(P.O.Box 238, N-1360 Nesbru, Norway) 
Commission V 
SUMMARY: 
Metrology Norway System is an industrial photogrammetry system based on high resolution CCD 
cameras measuring coordinates of laser spots or light emitting diodes. The system is a true on-line 
measurement system presenting results immediately, point by point. The Light Pen, a mechanical probe, 
turns the system into a 'Hand-Held Coordinate Measurement Machine'. A CAD module allows all 
measurements to be related directly to the CAD model as Closest Point Deviations. The system has a 
broad range of applications in automotive and aerospace industry. The paper presents the metrology 
concept, and focuses on applications with examples from Volvo, Saab Aircraft Division, and Fiat. 
KEYWORDS: 
1 INTRODUCTION 
The Metrology Norway System (MNS) presents a totally 
new concept for industrial metrology. It is a system that 
provides accuracy for most metrological applications, yet 
includes the features of rapid data collection over a large 
volume as well as system portability, which allows for 
extreme system versatility for a number of applications. 
The system is developed in close cooperation with Volvo 
Car Corp., Department of Production Technology. This 
ensures that the system is tailored to the industrial needs. 
The system is based upon specially manufactured and 
calibrated CCD cameras. The one-time factory calibra- 
tion converts each camera into an ideal on-line photo- 
grammetric camera. MNS measures the spatial (XYZ) 
coordinates of special infrared Light Emitting Diodes (IR 
LEDs), or alternatively, points of reflected IR laser light. 
This paper focuses on the measurement concept, as well 
as applications. The accuracy of the system is discussed 
in detail by Pettersen (1992). 
A new measurement concept, making 3D measurements 
using only one CCD camera, is discussed by Aamdal 
(1992). 
2 THE MNS CONCEPT 
2.1 Photogrammetry 
MNS is basically a photogrammetry system, based on 
high resolution CCD cameras (Videk MegaPlus). The 
cameras are interfaced to a VME based computer making 
high performance signal analysis, giving a sub pixel 
resolution of 0.01 pixel. 
To obtain an optimum accuracy, and to make the system 
easy operational, the cameras are factory calibrated. This 
calibration process involves a complete mapping of the 
  
CAD/CAM, Close-range, Industrial, Real-Time, 3-D 
entire sensor, giving a detailed description of lens distor- 
tions, sensor geometry and sensor defects. The result of 
the camera calibration, i.e. the interior orientation of the 
camera, is stored in the system computer, and is used to 
correct each observed image coordinate to that of the 
'ideal' photogrammetric camera. The calibration method 
is a unique proprietary technique developed and patented 
by Metronor, and will not be described in further detail in 
this paper. 
The factory calibration allows the camera to be used at 
any location without any calibration in the measurement 
setup. A simple set up procedure is needed to determine 
the relative position of the two cameras and the object of 
interest: 
- The cameras are easily aimed towards the object 
such that the fields of view of the cameras overlap, 
covering the volume which contains or will contain 
the object to be measured. The user is able to see 
the actual images from the cameras at the com- 
puter monitor. 
= The exterior orientation of the cameras, i.e. their 
relative position and orientation, is determined by 
the use of a Reference Bar as shown in fig. 1. The 
Reference Bar contains several infrared (IR) LEDs 
embedded in a bar made of the alloy Invar and is 
connected to the MNS System Console via a 
multi-purpose cable. The Reference Bar is aimed 
so that both cameras are able to view the LEDs. 
Pressing a button located on the end of the Bar 
causes a measurement to be taken. The user then 
changes the orientation of the bar, and the button 
is pressed again. For optimum results, measure- 
ments are taken throughout the entire intended 
measurement volume. This allows for maximum 
redundancy in the initialization routines. 
= The camera positions and orientations are then 
automatically calculated using the method of 
bundle adjustments. This essentially is a least 
squares analysis to fit the given distances between 
the light sources in all bar positions to the calcula-