Fig. 1. Camera Setup and Exterior Orientation 
ted positions and orientations of the cameras. The 
calculation routine displays the maximum and 
mean deviation from the certified length. The 
bundle adjustment algorithm does not require initial 
values for any of the parameters to be determined. 
= The results of the exterior orientation defines a 
global coordinate system. To relate all measure- 
ments to a local coordinate system, reference 
points are needed, having well known local coor- 
dinates. Two options are given: three reference 
points given by their x, y and z coordinates, or a 
maximum of six points given as a 3 - 2 - 1 sys- 
tem. A 3 - 2 - 1 reference system may as an 
example be given as three points defined by their 
z-values, two points by their y-values, and the last 
point by its x-value. The reference points are 
typically plane surfaces or holes. A simple tool 
used to measure reference points is the Light Pen, 
as described below. 
The system includes a UNIX based workstation, dedica- 
ted to application specific software, and user interface. 
2.2 The Light Pen 
MNS introduces the patented Light Pen (fig. 2), which 
makes MNS become a transportable Coordinate Mea- 
surement Machine (CMM) for applications requiring 
accuracies in the order of 0.1 mm. The Light Pen is a 
device allowing the user the freedom to digitize any 
selected point on an object. The user places the tip of the 
Pen on the selected point, ensures that the cameras can 
see the LEDs, and presses an exposure button on the 
Pen. The coordinates of the Light Pen tip are immediately 
presented at the computer display. 
The Light Pen contains three LEDs whose coordinates in 
the Light Pen's local coordinate system are well-known. 
With this knowledge of the Light Pen's geometry, MNS 
easily calculates the spatial coordinates of the Pen's 
stylus tip by measuring the spatial coordinates of the 
three LEDs on the Pen. 
  
Tip Selector Button 
Indicator LEDs 
Exposure Butto 
Twist Lever 
  
  
  
Fig. 2. Light Pen 
The interchangeable pen tip tool is analogous to a Coor- 
dinate Measurement Machine's probe/stylus combination. 
Each tool has been previously calibrated, either by 
Metronor or the user, and its stylus tip coordinates with 
respect to the Pen's local coordinate system are stored 
in MNS. The user is free to create unique styli to allow 
measurements in difficult to reach areas. To take a 
measurement, the cameras need only to see the LEDs 
and not the actual tip of the Pen. For instance, if the user 
wants to measure points underneath a surface of an 
object, a stylus could be bent into the shape of a hook. 
The Light Pen enables measurements of physical features 
like: 
Single XYZ Coordinate 
Distance between two points 
Holes - diameter and center coordinates 
Spheres - diameter and center coordinates 
Flush - the distance and relative angle between 
two surfaces 
Gap - the gap (distance) between two lines or 
edges 
* OR OR GER 0 
The light pen is an important tool for measuring the 
coordinates of reference points. 
2.3 Laser spot projection 
Various laser-spot projection systems are also available. 
The Laser Projector Gun is an ideal tool for measure- 
ments involving soft or foamy materials (i.e. those found 
in automobile interiors) that would deform if measured by 
conventional contact methods. As MNS measures the 
spatial coordinates of spots of infrared (invisible to the 
human eye) light, the Laser Projector Gun projects two 
visible lasers, as well as the invisible laser that is measu- 
red. The visible lasers are necessary for determining the 
correct focus and target point, as it is essential that the 
spot is in optimum focus to reduce or eliminate the effects 
of speckle. 
   
The 
mea: 
A du 
that 
proje 
the c 
nate: 
ned 
who: 
bear 
the : 
objet 
ning 
pora 
2.4 
MNS 
nomi 
perfc 
com| 
ponc 
The 
use 
VDA: 
Ethei 
MNS 
repre 
Durir 
appe 
inat 
taker 
the n 
grapl 
The 
meas 
neou 
catio 
2.5 
The € 
meas 
respe 
or an 
3.1 
Thes 
due t 
well a 
Inac. 
of 1.0