ACCURACY STUDY OF DIGITAL RESTITUTION PRODUCED FROM SCANNED 
1/40000 SCALE AERIAL PHOTOGRAPHS AT DIFFERENT RESOLUTIONS 
M. Cherkaoui-O.*, M. Rouchdi*, J. Massiji”, I. Solomay” 
* Département de Cartographie-Photogrammétrie, Institut Agronomique et Vétérinaire Hassan Il 
Rabat, Maroc (m.cherkaoui@iav.ac.ma) 
° Ingénieurs au secteur privé 
Commission VII, WG VII/3 
Key Words: Scanning — multi-resolution — restitution — mapping — scale — accuracy 
RESUME : 
La photogrammétrie a connu une évolution croissante passant par les procédés analogique, semi- analytique et analytique qui 
étaient bien développés durant la deuxième moitié du siècle précédent. Vers la fin du même siècle le procédé numérique qui 
est devenu possible avec l’augmentation des performances et la miniaturisation du matériel informatique ainsi que le 
développement de logiciels appropriés. Si le matériel informatique est devenu accessible à toutes les petites et moyennes 
entreprises topographiques, ces derniers ont du mal à acquérir une caméra numérique ou un scanner photogrammétrique 
nécessaires pour la production d’image photographique. Cependant, il existe sur le marché des scanners de moyennes 
résolutions, mais l’inquiétude réside au niveau de la précision des résultats à obtenir. Pour cela, cette étude a été réalisée pour 
tester les performances d’un scanner de bureau (EPSON de format A3) avec 4 résolutions différentes (300, 400, 600 et 800 
dpi). Les résultats de la restitution obtenus à partir des photographies au 1/40 000 numérisées avec ces résolutions ont montré 
que les normes de la cartographie topographique à l’échelle du 1/50 000 et inférieure sont satisfaites avec une résolution de 
800 dpi. 
ABSTRACT: 
For a decade, photogrammetry has known an important investment in infrastructure and equipment. Getting accurate 
coordinates from aerial photographs relies on long and difficult operations. Photogrammetric tasks need, also, that one 
should have enough knowledge about the optical, mechanical and digital systems used. Due to the rapid development of 
software and the high performance of hardware, digital photogrammetric procedures become widely used. Furthermore, the 
market offers, presently, a large variety of computers and scanners at low prices. Hence, most professionals in the 
cartographic field show interest in integrating the new technology in production tasks. However, they are in doubt of the 
product accuracy that will result using this technology. The main purpose of this research was to evaluate the accuracy of a 
digital restitution generated from two couples of aerial photographs at scale of 1/40 000(one couple covers a flat terrain and 
the other one a rudged terrain) scanned at three resolutions (400, 600 and 800 dpi) using a desktop A3 scanner. The analysis 
of results accuracy showed that topographic mapping at scale of 1/50 000 and lower is possible using a desktop A3 scanner 
and a resolution of 800 dpi. 
1. INTRODUCTION e An important decrease in price of video- 
restitution instruments which were brought to 
Photogrammetry has been always a synonyme of an replace analytical stereo-restitution 
important investment and reserved for only some instruments ; 
specialists. It is true that the used matierial ether analogic e The management of digital image is less costly 
or analitic is in general impressive. Ggetting acurate than the technology which is necessary for 
coordinates from photographic images needs elaborated controling the silver negative displacement in 
methods and good knowledge about mecanics, optics and terms of micron ; 
computer science based techniques. The use, e The democratisation of restitution instruments 
progressively, of video sensors since 1975, the increase in has made the photogrammetric technique 
preformance of micro-computers, has introduced a new affordable to some structures such as PME, 
field which is digital photogrammetry or video- PMI and research laboratories. 
grammetry (Egels, 1998). Since then, it has been a matter e The possibility of research development for the 
of digital image processing instead of direct manipulation purpose of procedures automatisation. 
of aerial photographies. Theses techniques have several 
consequances conséquences On photogrammetric Howver a problem persists: the possibility of 
restitution procedures (Duperet, 2001). acquiring, by all professionals, performant and 
costly material which satisfies the needs of 
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