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ANALYZING DMC PERFORMANCE IN A PRODUCTION ENVIRONMENT 
J. Talaya, W. Komus, R. Alamüs, E. Soler, M. Pla, A. Ruiz 
Institut Cartogràfic de Catalunya, 08038 Barcelona, Spain - 
(julia.talaya, wolfgang.komus, ramon.alamus, eulalia.soler, maria.pla, antonio.ruiz_g)@icc.cat 
Commission IV, WG IV/9 
KEY WORDS: Aerial Photogrammetry, Accuracy Assessment, Digital Photogrammetry, Accuracy Analysis, Topographic 
Mapping 
ABSTRACT: 
Since December 2004 the Institut Cartografic de Catalunya (ICC) has taken more than 135 000 digital aerial images with two Digital 
Mapping Cameras (DMC) from ZEISS/INTERGRAPH (Z/I). After three years of experience and with the new, fully digital, 
production lines well established, this paper analyses the performance of the digital camera in a true production environment, 
specially compared to the older production lines based on digitized analogue images.The accuracy assessment is studied for every 
single step of the mapping production line: aerial triangulation, DEM (Digital Elevation Model) generation, stereo plotting and 
orthophoto quality (image resolution). DMC images of 45cm and 7.5cm pixel size, from several production projects, are analysed 
and the results are compared to the respective results of analogue workflows (with the same pixel size when scanned at 15pm). The 
accuracy assessment for the aerial triangulation and stereo plotting is done with independent check points and with Lidar data for the 
DEM evaluation. The analysis of the photointerpretation is based on the observations of experienced and well trained operators. To 
asses the resolution of DMC images, a tool based on the computation of the Line Spread Function has been developed. The method 
takes into account the distance of this kind of structures to the center of the image, both along and across flight direction, in order to 
quantify the effective resolution power of the DMC and the analogue images.Final conclusions are drawn from the performance 
analysis of the aerial triangulation, DEM generation, stereo plotting and image resolution in a production environment. 
1. INTRODUCTION 
As a mapping agency in charge of most of the official 
cartographic production in Catalunya, ICC is flying every year 
in Catalonia an area of about 15000km 2 at a ground sampling 
distance (GSD) of 45cm and an area of more than 500km 2 at a 
GSD of 7.5cm. Thus, a large database of analogue and digital 
images is available for a direct comparison between the 
analogue and the new digital workflow in terms of accuracy and 
efficiency. 
During the validation process of the DMC at ICC some first 
conclusions about its performance were drawn (Alamus et al. 
2005). Now, three years after the implementation of the digital 
cameras at ICC, the main part of the learning curve has passed, 
the workflows are well established and many production 
projects finished; therefore, it is time to study the performance 
of the new fully digital workflows in comparison to the old 
analog ones. 
2. AERIAL TRIANGULATION 
In aerial triangulation (AT) ICC’s in-house adjustment software 
ACX-GeoTex is used, which is able to employ highly precise 
GPS/INS observations for exterior orientation parameters, 
ground control observations and additional self-calibration 
parameters. For accuracy assessment two major differences 
between the analogue and the digital workflow must be 
considered: 1. The DMC has a smaller base to height (b/h) ratio 
of 0.3 (caused by the rectangular DMC image format) 
compared to the b/h ratio of 0.6 in the case of conventional 
analogue frame cameras, resulting in a two times lower 
accuracy estimation of the point heights. 2. In the analogue 
images nearly all measurements were stereoscopically observed 
by experienced operators on digital photogrammetric 
workstations, while from 2004 onward, almost at the same time 
the first digital DMC camera was purchased, this part was 
gradually taken over by automatic AT techniques using Inpho’s 
Match-AT software, i.e. most of the digital images were 
aerotriangulated using a dense photogrammetric network of 
automatically derived tie points. The automatic image 
correlation also returned a significant higher accuracy applied 
to digital images than applied to digitized analogue photos, 
which compensated a good part of the accuracy loss caused by 
the lower b/h ratio. 
2.1 Improvements in image pointing accuracy 
During the validation of the first DMC camera in December 
2004 manual and automatic aerotriangulations were performed 
and compared to the manual aerotriangulation of an analogue 
flight taken in 2000 from the same area (15pm scanning 
resolution). 
The first topic to analyse is the point measurement accuracy 
applying semi-manual point identification in analogue and 
DMC images as well as digital image matching in the DMC 
images. Table 1 presents the pointing accuracy for semi-manual 
point identification in analog images, semi-manual point 
identification in DMC images (labeled DMC manual) and 
digital image matching (Match-AT) in DMC images. The Table 
shows an improvement by a factor of 1.3 comparing the semi 
manual point identification (point observation has been carried 
out using the semi-automatic tools provided by ISDM from 
Intergraph) of DMC and analogue images and even by a factor