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element contains, apart of its own exactly determined 
position, a definite information - grey value (Stefanovic et 
al., 1998). 
Since the image is generally not strictly vertical, the 
prespective image will deformed even in the case of 
strictly horisontal land. The transformation of thus 
defromed image into the corrected one that will 
correspond to the orthogonal plan projection in a certain 
scale is called redressing. The differential redressing 
makes it possible to obtain the image transformed not 
only into the orthogonal, but also to any other map 
projection (Lapaine and Francula, 1998). 
Digital orthophotoplan is a geometrically corrected 
photography in digital form resulting from the computing 
transformation of digital images from the central into the 
orthogonal projection. The process of computing the 
digital orthophoto plan can be devided into geometric and 
tone correction of the digitally scanned image. The first 
part encompasses the correction of scale errors and of 
prespective deformation, and the other part relates to the 
elmination of unequalities in the intensity of the 
blackening. The orthophotoplan is practically an 
orthogonal projection of the surveyed area and integrates 
thus the advantates of the classical geodetic plan and 
photoplan. The corrected photography is the basis for a 
map in photographic form - orthophotomap, 
supplemented by the contour lines or contour values 
charaterizing the terrain configuration or relating to the 
important positions, than by the toponomastic of the 
regions, municipalities, settlements, relief features, 
hydrography etc., by the symbols for geodetic points 
(trigonometric, orientation, levelling, possibly traverse 
etc.), by letter and number symbols accompnying the 
traffic routes and by other data (Biljecki and Tonkovic, 
1999). 
2.1 Cyclical survey in the Republic of Croatia 
In the West-European countries, the updating of maps is 
much more preferred than the production of new maps. 
For the purpose of updating, one plans cyclical 
photogrammetric surveys in the period of 3 to 7 years. On 
the basis of the obtained images the sheets of 
topographic maps at a definite scale are produced (State 
Geodetic Administration, 1995). 
In the period between 1990 and 1996, the aerial survey 
has been interrupted because of the war and the fighting 
for the independence of the Republic of Croatia. While the 
war was still going on, the experts were already thinking 
about the period after the war and about the 
establishment of aerial photogogrammetric service. 
Referring to the war conditions, the State Geodetic 
Administration has made a decision to start with cyclical 
surveying in the northwestern part of the Republic of 
Croatia, at the territory of Istria. In 1996 the western part 
of Istria from Umag to Pula (on Fig. 1 the area is marked 
by the hatching with thin line density) was surveyed. After 
the state needs had been thoroughly analysed, the 
decision was made to continue with cyclical survey 
according to priorities. Hence, in May 1997, the 
northwestern part of Croatia was surveyed. At the same 
time, the surveys started to be performed in the 
southwestern part of Croatia. Due to very good weather 
conditions, one started with surveying at the territory of 
Lika, and of the cities Zadar, Sibenik, Split. Because of 
the new situation in Slavonija, and because the war 
stopped and it was necessary to collect the photographic 
material of the devastated area, this area started to be 
surveyed. In the meantime, it was urgent to survey a 
broader area of the City of Zagreb to widen earlier 
planned area of Lika - Zadar - Sibenik - Split (Landek 
and Kauric, 1998). On Fig. 1 the areas photographes in 
the period between 1997/98 are marked by the hatching 
with medium line density. For the period of 1999/00 all 
other areas have been covered by agreements and partly 
photographed, and they are marked by hatching with the 
highest density of lines on Fig. 1. 
High quality photographic magnifications at the scale of 
1:10 000 or 1:20 000 can be made from aerial 
photographs at the scale of M s = 1:31 600. Referring to 
the legibility of a negative of at least 50 lin/mm, it is 
possible to spot the details having the absolute size of 9,5 
m. Wit good magnification one can expect the legibility of 
details at the magnifications of at least 1 m which is 
rather satisfactory for the scale of 1:10 000 (State 
Geodetic Administration, 1995). 
3. APPLICATION OF AERIAL PHOTOGRAPHS 
The application of photogrammetry in Croatia has so far 
been oriented mostly towards gathering and processing 
land and topographic data, i.e. more recently to the 
creation and establishment of land databases, mostly 
within the frame of geodetic spatial system (GEOPS) as 
the basic infrastructure for almost all activities dealing with 
space, and for the most spatially connected information 
systems. Thus, the exceptional importance of 
photogrammetry for the processes of spatial arrangement 
and systematic environmental protection, as very 
important tasks of a modern man is manifested. Referring 
to the experiences gathered and to the solid 
preconditions, it is not unrealistic to expect such a trend to 
be continued in our country in the future as well, but 
resulting in even better achievements (Krizaj, 1998). 
The development of digital photogrammetry has 
influenced remarkably the increase of the demand in 
scanned aerial photographs. Digital aerial photographs 
have been used lately in the first place for the purpose of 
producing digital orthophoto plans. Except for geodetic 
purposes, the scanned aerial photographs can be applied 
in other branches as well, e.g. in archaeology, geology, 
geography, hydrotechnics, agriculture, forestry, 
environmental protection, for military purposes etc. In 
order to avoid long lasting terrain reconnaissance, 
individual details of a certain area can be studied 
thoroughly by means of scanned aerial photographs, and 
also used at the beginning of making a conceptual design. 
One needn’t point out their application in the area of civil 
engineering and architecture, especially now, in after war 
period, for the purpose of ruined and in the war damaged 
objects, and to make urban plans, as well as for other 
purposes where visual terrain presentation is necessary 
(Landek and Kauric, 1998). 
Maps, and aerial and satellite images are the main data 
source for GIS. Applications of GIS are rather numerous: 
national and regional planning, environmental protection, 
natural resources management, military planning, city 
administration, land register and land register book, etc