PHOTOGRAMMETRIC SYSTEM CALIBRATION 
Pasi Laurila, Lic.Tech. 
Hannu Salmenperä, Assoc. Prof. 
Tampere University of Technology 
Department of Civil Engineering 
Geodesy and Photogrammetry 
P.O. Box 600 
SF-33101 Tampere 
Finland 
Commission IV, Working Group 4 
KEY WORDS: Accuracy, Large Scale Mapping, System Calibration, Test Field, Training. 
ABSTRACT 
System calibration means a process where the main purpose is to establish the overall accuracy of survey results. It is also 
important to analyse those factors which are critical for the accuracy. System calibration integrates instrument calibration and 
testing of survey methods, programs and personnel in one process. A photogrammetric survey for mapping or for digital terrain 
model is a complex process, where the human factor, the stereo-operator, is in key position. Also the properties of ground objects 
are quite often such that there are problems to identify and to locate them. Photogrammetric system calibration makes it possible to 
handle these kinds of problems, which are beyond easy control under operational conditions. This report describes the experiences 
of photogrammetric system calibration obtained in Tampere University of Technology, Finland. The reference used is the 
calibrated stereomodel of Rusko, which is an accurately surveyed test field for large-scale photogrammetric mapping. It gives us 
the means to establish the accuracy of photogrammetrically mapped coordinates in various point classes, to evaluate the capabilities 
of stereo-operators and to train them. It has also been possible to find out the critical parts of the photogrammetric survey process. 
They are the resolving power of the photography, the image deformations due to heat in the stereoplotter, the stereo-operator's 
skills, and the characteristics of ground objects. Accordingly, the training of stereo-operators seems to be an important way to 
improve mapping accuracy. Other important things are improvement of the resolving power of the camera/film combination, 
image motion compensation, the careful handling of photographs throughout the process, and the control of image deformations in 
the stereoplotter. In the future use of digital images will improve the survey process, for example, in respect of image 
deformations. 
instrument calibration and theoretical considerations only. 
Here we propose a concept and methods of system calibration 
The design of civil engineering projects requires data about to establish the accuracy of the final mapping products, and to 
the terrain surface in the form of plans, maps, and digital analyse those factors which are critical for the accuracy. 
elevation and terrain models. As planning methods are getting 
more sophisticated and accurate than ever before, this sets new 
requirements for the survey data. Especially geometric 
accuracy must be higher than before. Today most of this survey 
data is generated by photogrammetric methods. Modern Definition 
cameras are accurate instruments, as are analytical and digital 
stereoplotters, too. Their accuracy can be tested by instrument — Traditionally calibration is understood as instrument 
calibration. But they are only part of the photogrammetric calibration which establishes the accuracy of the surveying 
survey process. The rest involves for example the execution of ^ instruments. That is necessary but not enough for complicated 
the flight missions, the photographic properties and survey processes. What is needed is system calibration. It 
deformations of the films, the personal capabilities of the means a process where the purpose is to establish the overall 
INTRODUCTION 
PHOTOGRAMMETRIC SYSTEM CALIBRATION 
  
stereo-operators, the accuracy of the control points, and the 
properties and interpretability of terrain details. In many cases 
the accuracy of stereophotogrammetry in mapping applications 
has been overestimated. One can see several reasons for this. 
First, the accuracy figures are mainly related to targeted or 
otherwise well-defined points. Second, the personal 
capabilities of the stereo-operators have not been considered 
properly. And third, the difficulties to identify and to locate 
terrain points and other features have not been taken into 
account. These are matters which cannot be handled with 
accuracy of the survey results. It integrates instrument 
calibration and testing of survey programs, methods and 
personnel in one process which follows the steps of the real 
survey process. This is a very demanding task, especially 
when one wishes to analyse the results thoroughly. In fact it is 
not always possible to find out all the reasons and connections 
which have an effect on the accuracy from the results of system 
calibration alone. In this respect the conventional methods of 
instrument calibration are important, too. The above definition 
involves more than the well-known photogrammetric test field 
486 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996 
  
calil 
the 
accu 
vari 
neec 
expe 
(Nis 
Cali 
Testi 
The s 
whic] 
or sh 
perso 
Espex 
of sy: 
to te 
them. 
The c 
of th 
contri 
mark: 
Opera 
the c« 
rando 
mark: 
meas