International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B3. Istanbul 2004 
  
Figure 2: Left: The Canny output map. Right: The Rothwell 
edge map. 
The input parameters to the /verson-Zucker algorithm were the 
following: a) Threshold (7), number of directions (d) for the 
algorithm to follow (1-16), degrees of freedom based upon the 
number of directions (4-64), the output detection type (E 
(edges), P (Positive lines), and N (Negative lines)). The best 
output result (0.4967) (Table 1) was derived using 16 directions 
and 7=0.015. 
The input parameter to the Black algorithm was the smoothing 
coefficient (c) in the range (0, 1]. The best output edge map 
resulted in the highest Pratt metric (0.4773) (Table 1) using 
0=0.25 (Figure 3). 
  
Figure 3: Left: The Iverson-Zucker output map. Right: The 
Black edge map. 
The input parameters to the SUSAN algorithm by Smith and 
Brady were: (a) Brightness threshold (-7) (default = 20), (b) 
distance threshold (-d) (default = 4.00) (used instead of flat 3x3 
mask), (c) use of flat 3X3 mask (-3), (d) choice among edges (- 
€), smoothing (-s) or corner detection (-c) modes. The best 
output result (0.3171) (Table 1) was derived for 7715.00 
(Figure 4). 
  
Figure 4: The SUSAN output map. The edges are depicted 
with black lines and overlayed on the smoothed image. 
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Using the EDISON algorithm, the best output edge map 
(0.4507) (Table 1) was derived using the following combination 
of parameters: a) Gradient=2.00, b) Minimum length=5.00, c) — 
e) Nonmaxima suppression: Type=arc, Rank-0.5 and 
Confidence-0.4, f) — h) High Threshold for hysteresis: Type — 
box, Rank=0.91 and Confidence=0.92, and finally, i) — k) Low 
Threshold for  hysteresis: Type=arc,  Rank-0.98 and 
Confidence-0.93. 
Finally, the parameters used in the Bezdek algorithm are: (1) 
Tau, in the range [0.0...5.0], (2) Chi, as a function 
HTau)=2.0*Tau, (3) Gamma, as f(Tau)=2.0*Tau, (4) Omega, as 
function of f{Tau)=3.0*Tau, (5) Binary Threshold, which is in 
the range [0...GRAY LEVELS — 1] and (6) Edge Features 
(Sobel). The best result (0.4428) (Table 1) was obtained for 
Tau=1.00 and Binary Threshold=80.00 (Figure 5). 
  
Figure 5: Left: The EDISON edge map. Right: The Bezdek 
edge map. 
In a similar manner and logic, the selected edge detection 
algorithms were further applied on the DEM of the same area, 
and, only two of the best results as judged by 
photointerpretation (Table 1) are presented in Figure 6 due to 
paper size constraints. 
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Figure 6: (a) Based on DEM processing: the Canny edge map 
(left) and the EDISON edge map (right). 
In the Canny algorithm, the parameter set with the highest score 
of the Pratt evaluation metric (0.4332) (Table 1) was for 
o=1.50, Tlow=0.30 and Thigh=0.70. 
In the EDISON algorithm, the best output edge map (0.4359) 
(Table 1) was derived using the following combination of 
parameters: a) Gradient=2.00, b) Minimum length=4.00, c) — e) 
Nonmaxima suppression:  Type=arc,  Rank-0.5 and 
Confidence=0.7, f) — h) High Threshold for hysteresis: Type = 
box, Rank=0.93 and Confidence=0.96, and finally, i) — k) Low 
Threshold for hysteresis: Type-arc, Rank=0.97 and 
Confidence=0.93 (Figure 6). 
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