GEOMETRIC AND RADIOMETRIC ANALYSIS OF A The € 
PHOTOGRAMMETRIC IMAGE SCANNER as 
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Bolte, Uwe, Jacobsen, Karsten, Wehrmann, Hagen 245m 
University of Hannover, Germany aerial 
Email: karsten@ipi.uni-hannover.de 
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KEY WORDS: Geometry, Radiometry, Digitization, Image, Scanner integr 
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ABSTRACT: TDI-s 
The digital (hardcopy) photogrammetry makes a very fast progress, but for aerial photogrammetry the primary data e 
acquisition will be based in the near future on analog photos. The loss of geometric accuracy and the loss of This 
radiometric information caused by the scanning of photos with the photogrammetric image scanner Rastermaster : 
RM1 of the University of Hannover has been investigated. image 
The dynamic range of the TDI sensor included in the scanner is limited to 1.5D and the relation between the gray 
values and the photographic density is not linear. That means there is a loss of information especially in the dark The F 
parts of the scanned images. This can be accepted for positive black and white or color film, but it is causing part c 
problems with negative films. The scanning of color images with filters will not led to optimal results in the blue the ce 
spectral range. These problems are not special problems of the Rastermaster, it is a general problem of the CCD- a sele 
linear arrays and CCD-arrays. 1060! 
red/gr 
The geometric accuracy of the Rastermaster is corresponding to an analytical plotter, that means it is sufficient for all fluore 
purposes of digital photogrammetry. D ler 
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the se 
1. INTRODUCTION intensively used. If a scanner is available, the request for 
The amount of information included in an aerial photo digital images automaticelly is raised. 
cannot be transferred with the today technique into any 2. THE RASTERMASTER RM1 
type of storage within the time period available from ih 
exposure to exposure. By this reason also in the next ue AM ino ovis RH e Pace Neher 1904 If the 
future photos have to be scanned for getting digital is. flow different NS the A es a y. e om d. with prod. 
images with sufficient resolution. Line scanners do not Hah d d | g ; ilable. Th is imr 
have the number of pixels corresponding to a photo gae Speed n0 d SOT Sensor I9 avatlable. e corre: 
(418400 pixels would be required) and the geometry geometric behavior iS the same, only Some parts ars to the 
reconstructed for improving the life time and reducing the 
cannot be compared. ; : not L 
required service. 
It has been shown that only image scanners designed for stanc 
photogrammetric purposes do have a sufficient accuracy. fluorescent lamp has € 
Drum scanners with diodes do have a better radiometric Te with - 
characteristics than CCD-lines and arrays but the filter wheel highe 
geometric quality is usually not better than +50um, or with be r 
some special calibrations of new scanners +25um and Jacol 
this only can be accepted for orthophotos. Image 
correlation, data acquisition for aerial triangulation and The I 
photogrammetric stereo measurements have to be based analy 
on digital images with position accuracy's not less than 
+5um. 
Because of the limited budget of the Institute the 
photogrammetric image scanner Rastermaster RM1 from 
Wehrli & Associate Inc. has been chosen. Our version of 
the RM1 needs including the handling 30 minutes for the 
scanning of an aerial photo with 12um pixel size. All the 
other technical details are corresponding to the other 
photogrammetric image scanners. In the meantime the 
scanning speed has been changed by Wehrli Ass.. 
During the decision phase the amount of images which 
have to be scanned was underestimated, this seems to 
be typical. In the period of now 14 month the scanner was 
G photo carrier 
TDI-sensor 
= optics 
br Sn 
  
  
  
  
  
  
  
  
  
  
Figure 1: configuration of the Rastermaster RM1 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B1. Vienna 1996