THREE-DIMENSIONAL CONTROL 
OF SHIP CONSTRUCTIONS 
Haggrén, Martikainen, Salmenperá, Vehkaperä 
and 
Väätäinen 
Technical Research Centre of Finland 
1. INTRODUCTION 
The photogrammetric methods in measuring and 
interpreting shapes of things have been devel- 
oped mainly for mapping purposes. They have 
recently been acknowledged as a most advanta- 
geous, sometimes even as the only possible so- 
lution to various problems in the field of 
engineering survey /l...2/. 
The photogrammetric methods are especially well 
suited for solving problems in which one has 
a great number of points to be measured and in 
which the object to be measured is three-di- 
mensional (shape, size, volume) or in which 
the object is mobile (deformations, movements) 
or in which the object is intangible. The 
measurement problems in industry are on a more 
general level than in mapping, so much so that 
the readiness to perform this kind of measuring 
tasks and especially to produce results in use- 
ful form has been quite poor. The coordinate 
lists which are the only output of an ordinary 
process are impractical and necessarily need 
graphical presentation in order to be effec- 
tively utilized. 
Nowadays ships are often fabricated of large, 
readymade elements which may be transported 
over long distances for assembly. The shape 
and size of the elements are controlled by con- 
vential mechanical measuring methods. Ship- 
builders have found these methods rather im- 
practical, slow and inaccurate in many tasks. 
On many occasions, those responsible for the 
control measurements have manifested their in- 
terest in modern methods which might have 
better correspondence with the requirements 
of today's shipbuilding. 
The aim of the research work was to develop 
a flexible measuring method which would be 
suitable for the measuring of the shape, size 
and deformation of different kinds of ship- 
blocks and which would provide a proper graph- 
ical presentation of the results. 
72 
In the first phase of the project, software 
was developed for the simultaneous computation 
of geodetical and photogrammetric observations. 
Furthermore, programs were developed to pro- 
duce graphical output on the basis of adjusted 
coordinates. 
2. THE MEASURING METHOD 
The purpose of the measuring method is to de- 
termine the shape and size of a construction. 
The shape of a construction is measured as 
three-dimensional coordinates of the object. 
The scale of the model is determined by the 
distances between the control points targeted 
on the object. The results of measuring are 
stored in a coordinate file used as a base for 
numerical, statistical and graphical presenta- 
tion. The mathematical fundamentals and the 
accuracy of the method have been published, 
among others, by Hottier /3/ and Wong /4/. 
A description of this measuring method is filed 
in the register of test methods at Technical 
Research Centre of Finland /5/. The software 
needed in the method is documented in the prog- 
ram abstract register of technomathematical 
programs at Technical Research Centre of 
Finland /6/. 
2.1 Description of the method 
At first, the construction to be measured and 
the object points on it must be fixed. If the 
results are to be presented in the coordinate 
system of the object, this must be fixed. ALL 
points to be measured must be targeted. The 
control points must be so selected that the 
distances between them are approximately equal 
to the dimensions of the construction. The 
control distances are measured with a steel 
measuring tape. 
The camera stations must be so selected that 
every targeted point can be seen on at least 
one pair of photos, the base being about the 
same as the distance from the camera to the 
object. The photography is done with a metric 
camera using glass plates. Every point to be 
measured is marked and numbered on the positive 
copies of the photos. The glass-negative pho- 
tos are measured in a comparator. Two poin- 
tings are made on every measured point. 
On the basis of the control distances and the 
calculated image coordinates of the points, a 
numerical spacemodel is computed using a gen- 
eral three-dimensional adjustment program. 
The inaccuracy of the result, due to the mea- 
suring method and expressed as a standard error 
of one coordinate, is at most t 2mm. The in- 
accuracy is also affected by the errors arising 
from the identification and targeting of the 
object points. 
2.2 The software for computation of obser- 
vations 
In the beginning of the project, a three-di- 
mensional adjustment software was developed. 
The following types of observations can be ad- 
justed simultaneously: 
- horizontal angles, 
- vertical angles, 
- height-differences, 
- slope distances,