E. DD 
  
Figure 13: Detected roads using Ziplock Snake 
According to the literature, the implementation area of Ziplock 
Snake consists of non-salient roads, indeed. As shown in figure 
14, Ziplock Snake detect roads for a simple image that is 
modified by user to generate synthetic shadows. 
Figure 10(c) Figure 13 Average 
Correctness 9488.57 9483.45 %86.01 
Completeness %97.74 %100 %98.87 
Image Size (pixel) 347x435 349x303 
  
Table 6: Evaluation of Ziplock Snake for salient roads 
  
Figure 14: Detection of roads for simple image that is modified 
by user using Ziplock Snake 
  
(a) (b) 
Figure 16:(a) Ziplock Snake with Gaussian Kernel (15x15) (b) 
Ziplock Snake with Gaussian Kernel (10x10) 
Figure 14 Figure 15 Average 
Correctness %72.43 %55.83 $964.13 
Completeness 9498.79 %99.13 %98.96 
Image Size (pixel) 344x434 513x437 
  
Table 7 : Evaluation of Ziplock Snake for non-salient roads 
A failure case is shown in figure 17. Causes of failure in this 
experiment are; using unsuitable Gaussian kernel filter, manual 
representation of elasticity and rigidity parameters, and similar 
geographic properties of roads and other features. 
  
Figure 17: Failed detection using Ziplock Snake 
3.2.3 Optimization 
Optimization of the snake starts using initial snake that is 
defined by initialization procedure. In the optimization 
procedure the Ziplock snake is divided into three parts by two 
force boundaries (Neuenschwander et al. 1997). During 
optimization procedure the modified equation 
fa Kr em pelle oq: .-F* 
(K "rhy I) Y —Y'Uvs ie Fr 
is iteratively solved for the active vertices. y is a similar 
viscosity term of traditional snake. 
Ziplock snake needs initial end points and this algorithm is 
applied between these end points. During optimization 
procedure, new force boundaries are obtained and force 
boundaries meet at the center of the snake. 
3.3 Non-Salient Road Extraction with Ribbon Snake and 
Ziplock Snake 
Non-salient roads can be detected by using Ribbon Snake and 
Ziplock Snake together. If Ribbon Snake does not extract all 
roads in an image, Ziplock Snake completes undetected roads 
using the end points of detected roads. Figure 18 shows 
detection of roads using Ribbon Snake and Ziplock Snake 
together.