Close-range videometry - 
Design and calibration of a 
mono-camera system for dynamic purposes. 
Ivar Maalen-Johansen 
Dept. of surveying 
Agricultural Univ. of Norway 
WG V/1 
Abstract. 
The demand for measurements of a moving surface inside a small vacuum-chamber is meet by designing a 
special videometric system described in the paper. 
Because of initial space restrictions, one miniature CCD-camera together with mirrors form a split-image 
system. Calibration of this system includes additional parameters to describe the distortion of the optical 
system. 
Reduced radiometric resolution and use of only one video-field makes it possible to register a sufficient 
number of subsequent images in the internal buffer of the framegrabber. The effects of the special solutions on 
the accuracy are regarded in order to meet the accuracy requirements. 
Keywords: 
Videometry, close-range, split-image, calibration, system design. 
1. Introduction. 
The task of studying the condition of cow-teats during an 
automated milking process is desirable from an agricultural 
researchers point of view to optimize the process. Today the 
only possible insight into the process is a manual examination 
of the teats before and after milking. 
  
     
       
  
feat —— — 1 
C 
   
teatcup 
FA ‘liner —— 
  
  
  
  
vacuum 
milk 
  
  
     
   
   
    
  
Figure 1. Overview of the original milking machine. 
The aim of our project was to determine some unknown 
parameters of the milking process, such as distribution of the 
pressure from the teatcup liner on the teat. 
It is vital to the success of the milking process that the impact 
from the teatcup liner on the teat is correct. The pressure from 
the liner is to maintain the initial shape during the massage 
phase. Among the consequences of defective pressure are 
slower milking and risk of udder disease. 
To estimate the forces between liner and teat it is necessary to 
know the shape of the liner through the cycle. A number of 
surface-models have to be measured without disturbing the 
function of the teatcup liner inside the vacuum-chamber. 
Therefore no sensors can be fixed directly to the liner. 
In addition, it should be possible to collect the measurements 
in the cow barn environment. 
These reasons led to a proposal to make use of the remote 
sensing features of digital photogrammetry. A cooperation 
between two departments at the Agricultural University, Dept. 
of Surveying and Dept. of Agricultural Engineering, resulted in 
the videometry system described in this article. 
We have emphasized the calibration of our system since we are 
using both an "off-the-shelf" CCD-camera with no high-grade 
optics and have included mirrors in the imaging system. This, 
besides the sources of error in the CCD-technology, makes the 
camera modelling and calibration fundamental tasks in a system 
build-up. 
The calibration used in this system is a on-the-job calibration 
where a calibration frame is imaged in the place of the teatcup 
liner.