The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008 
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• Large image footprint (39 MP) 
• Ruggedised metric design - fully calibrated systems 
• Short exposure interval (2-3 sec.) 
• Compact systems suitable for small single-engine aircraft 
• RGB or CIR by changing lens filter (limitations in CIR) 
3. COMPARISON TO LARGE FORMAT CAMERAS 
Compared to large format mapping camera medium format 
cameras have some distinct technological differences, which are 
compiled in 
Table 1. 
Medium format 
Large Format 
Technology 
Camera 
Single head 
Multiple heads 
Image Size 
Max. 39 Megapixel 
Max. 136 Megapixel 
Colour 
Either RGB or 
(CIR) 
Separate heads, (Pan, R, 
G, B, NIR) image fusion 
Lenses 
Interchangeable 
Fixed 
Airborne system 
FMC 
Only mechanically 
TDI 
System cost 
Low 
Expensive 
System weight 
Light 
Heavy 
Energy 
consumption 
Low 
High 
Table 1: Main differences between medium and large format digital 
camera systems 
Beside the technological differences the vertical range of 
manufacture of digital medium format cameras and large format 
cameras is quite different. While in large format cameras all 
components are developed, optimised and tested for airborne 
applications, medium format camera systems including the 
processing software are often a composition of several off-the- 
shelf products for professional photographers combined with 
special features for the airborne environment. 
One of the main advantages of medium format cameras is the 
lower system price and the possibility to fly with small and 
cheap aircraft. The overall cost and the effort for an aerial 
survey and subsequent ortho photo production are related to 
many factors of the photogrammetric workflow. The 
comparison of the different processing steps reveals that the 
major advantage of medium format cameras are the lower costs 
for the aerial survey and the easier and faster postprocessing of 
the images of the single head cameras. Assuming an automatic 
tie point matching and a precise GPS/INS the cost of 
aerotriangulation is not very much higher for medium format 
cameras because this is normally a highly automated procedure. 
Due to the smaller ground coverage of an image more ground 
control points may be necessary. Nowadays the 
photogrammetric block does not necessarily rely solely on 
ground control points, but even for an integrated sensor 
orientation and quality assurance a certain number of ground 
control points are necessary, depending upon the number of 
images taken. The refinement of the seamlines between 
adjacent images is one of the manual and labour intensive step 
in digital ortho photo generation. Due to the relatively large 
number of medium format images, more manual labour is 
necessary for the generation of a seamless ortho photo mosaic. 
Together all of the factors lead to a lower cost reduction per 
area, compared to large format cameras, making medium format 
cameras less competitive for large area surveys. 
A big advantages of medium format cameras are 
interchangeable lenses with focal lengths of 35 mm to 210 mm. 
Different lenses allows missions to be flown at different 
altitudes to either maintain the desired resolution or maintain a 
predefined strip width during joint flights with others sensors, 
e.g. laserscanning. Also with interchangeable lenses the stereo / 
DEM capabilities may be changed as well as occlusions in 
narrow streets etc. during ortho photo production. However 
lenses with a long focal length generally cause several special 
problems in terms of their interior orientation and calibration. 
3.1 Geometric Potential 
The achievable geometric potential of a digital camera is related 
to the “metric” properties of the camera, which stands for a 
determinable and stable interior orientation. 
3.1.1 Interior Orientation 
The determination of the interior orientation of CCD-colour 
sensors based on the Bayer-pattem is related to some general 
sources of error due to longitudinal and transversal chromatic 
aberration, Cronk et al., 2006. However these errors are 
relatively small and only applicable for close range applications 
at the highest precision. 
However the airborne environment imposes special 
requirements on the camera system. To survive the shock and 
vibrations experienced in the airborne mapping environment a 
rigid camera body and a fixed lens mount is necessary for a 
stable interior orientation. Large format cameras generally 
operate with a fixed lens aperture. On medium format cameras 
the lens aperture is generally set by the amount of light 
available and the requirements of the shutter speed to minimise 
image movements. The lens aperture changes the interior 
orientation to a small extent. Also the work with 
interchangeable lenses requires a new (on the job) calibration 
every time the new lens is mounted. Even with a ruggedised 
design and special locking mechanism of the lens mount, some 
parameters of the interior orientation (especially the focal 
length) may change in the airborne environment due to changes 
in the air pressure when flying at higher altitudes. This is of 
special relevance for direct georeferencing, because the errors 
in the interior orientation are directly visible in the accuracy of 
the object coordinates. Therefore a simultaneous on the job 
calibration in terms of an integrated sensor orientation should 
be done. 
3.2 Minimum GSD of medium format cameras 
Customers are demanding higher and higher ground resolution. 
The highest possible ground resolution (GSD) for aerial surveys 
with standard endlap (60 %) depends on several factors such as 
the image exposure interval of the camera At and blur due to 
image motion. The exposure interval is related to the endlap p 
(in percent), the velocity of the aircraft over ground (v g ), the 
GSD and the number of pixels (n p ¡ x ) of the CCD-Sensor in 
flight direction: