The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008 
1230 
(Volpe, 2003). In fact, the number of GCP’s down to 4 / 5 did 
not decrease the accuracy significantly and sub-meter accuracy 
can be achieved using only a few GCP’s and the RPC models 
(Baltsavias et al., 2006; Fraser et al, 2006; Michalis and 
Dowman, 2006). Besides, a well spread distribution of even a 
few GCP’s is more beneficial to accuracy improvement than a 
dense but poorly spread distribution (Li et al., 2000). 
In this study, 12 GCP’s were established and marked in May 
2002 before recording of images. The coordinates of these 
GCP’s have been measured with Global Positioning System 
(GPS). These GCP’s have been used with different distributions 
in the orthophoto productions. 
2.3 Images 
Stereo-pair IKONOS (dated August 4 th , 2002), mono Quickbird 
(dated May 26 th , 2002) and 1:16.000 scaled aerial images (dated 
August 29 th , 2002) were provided by Inta Inc. (Turkey), 
Eurimage (Italy) and General Command of Mapping (Turkey) 
free of charge. The information about images are in Table 1. 
lfcoo-3 (Pas-1) 
Nirengi-2 
Pa$2 
❖ 
Pas-30 
❖ 
Pas-22 
❖ 
313 
A (Pas-5) ^ 
Pas-€003 
❖ A 
P as-20 m 
Pas-9 
❖ 
Pas-7 
P as-8 ^ 
o 
312 
A 
Pas-12 
❖ 
Pas-29 
❖ 
Pas-13 
❖ 
1308 
A 
Pas-24 
❖ 
302 
A 
Nirengi-3-lNirengi-3 
❖ ❖ 
309 
Pas-25 
❖ 
317 
A 
1315 
A 
3(3 
Jl 
Pas-15Pas-27 
❖ ❖ 
Pas-16 
t^as-17) 
o 
Niren» 1 ' 
❖ Q 
Nominal 
Collection 
Azimuth 
Nominal 
Collection 
Elevation 
Sun Angle 
Azimuth 
Sun Angle 
Elevation 
IKONOS-1 
343.397 0 
79.1812° 
145.587° 
64.083 ° 
IKONOS-2 
206.640 0 
65.7324 0 
146.031 ° 
64.182° 
Quickbird 
239.034 0 
83.0699 0 
139.486° 
67.278 ° 
Table 1. Azimuth and elevation angles of satellite images 
Figure 1. Distribution of GCP’s (A) and CP’s (O) 
The last DEM has been produced from IKONOS stereo images. 
8 GCP’s and 34 tie points were used in this process and a 
correlation success percent of % 97.2919 was obtained after 
production. It can be accepted that the accuracy of IKONOS- 
DEM is approximately ± 2 m (Erdogan, 2008). 
1:16.000 scaled 40 stereo aerial images have been taken in 5 
strips (in east-west and west-east direction) using kinematic 
GPS technique. The overlaps between the images and the strips 
were % 60 and % 30 respectively. 
2.4 Check Points (CP’s) 
Easily-recognizable and well-distributed 35 CP’s such as road 
junctions and field comers were selected from orthophotos and 
mosaic images. However, because of the time difference 
between images and land measurements, the weather conditions 
and the travel restrictions, only 27 CP’s coordinates could be 
measured with GPS (Figure 1). 
The field applications have been realized during two days in 
March 2003 using two reference points. 
2.5 Digital Elevation Models (DEM’s) 
Photogrammetric, cartographic and Ikonos DEM’s are used for 
different orthophoto productions. 
The photogrammetric DEM was produced by collecting data 
manually from 1:16.000 scaled aerial images in 20 m intervals 
(i§can et al., 2004). It is considered that the accuracy of 
photogrammetric DEM is approximately ± 1 m. 
The cartographic DEM has been already produced by General 
Command of Mapping using printed sheets in 1:25.000 scale. In 
this production, the printed sheets have been scanned first and 
then the contour lines have been digitized through semi 
automatic methods. It can be considered that the accuracy of 
cartographic DEM is approximately ± 5 m. 
3. GEOMETRIC ACCURACY ASSESSMENT 
For geometric accuracy assessment, orthophotos from satellite 
images and mosaic images from aerial photographs have been 
produced first. Then, check points (CP’s) have been selected 
from both orthophotos and mosaic images and finally, ground 
and image coordinates were measured and compared. 
3.1 Orthophoto and Mosaic Production 
Using photogrammetric, cartographic or Ikonos DEM, various 
ortho and mosaic images have been produced with different 
GCP’s distributions. Minimum 4/5 GCP’s and maximum 7-11 
GCP’s have been used in ortho and mosaic productions. 
Furthermore, a stereo IKONOS image (using 7 GCP’s and 91 
tie points) and orthophotos without GCP’s were also produced 
using direct sensor orientation. In orthophoto productions from 
satellite images, the rational polynomial coefficients (RPC’s) 
approach has been applied with a polynomial third order 
refinement. 
3.2 Coordinate Measurements 
Planimetric coordinates of the CP’s have been measured on all 
orthophoto/mosaic images and stereo IKONOS model. These 
coordinates have been compared with GPS coordinates. 
Because of big time difference between images and 
measurements, some difficulties have been encountered in 
detection of features on images and in finding the relevant CP’s 
in field. Therefore it has been tried to find the pixels which 
have the same grey scale values and represent the same features. 
In this process, it was very beneficial to use the brightness or 
darkness of adjacent pixels as described in Helder et al. (2003).