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A METHOD FOR BUILDINGS CHANGE DETECTION BASED ON VERTICAL EDGES 
EXTRACTION 
Tiantian Feng 3 *, Mi Wang 3 , Jianya Gong 3 
d State Key Laboratory of Information Engineering in Surveying, Mapping and Remote Sensing, 
Wuhan University, 129# Luoyu Road, Wuhan 430079, China - fancyftt@163.com, (wangmi,jgong)@lmars.whu.edu.cn 
KEY WORDS: Vertical Edge, Change Detection, Vanishing Point, Photogrammetry, Edge Extracting, Line Detection 
ABSTRACT: 
This paper proposes a method for buildings change detection. Vertical edges of buildings are extracted in pairs of aerial images 
respectively, taking advantage of the character that vertical edges intersect at their vanishing point without fail. The ground 
coordinates of the vertices on each vertical edge are calculated according to projection difference and the principle of frontage 
intersection. And the changes of buildings are detected by carrying on the change analysis using these coordinates and the three 
dimensional city models. Finally, experiments are given. The results show that the approach proposed by this paper is feasible and 
the changes of buildings can be detected accurately. 
1. INTRODUCTION 
City is the centre of population, economy, infrastructure and 
culture in the earth. With the rapid developments of the 
economy, the changes of cities are more and more prominent. 
And the researches on urban change detection are widely 
considered by scholars. At present, there are two kinds of 
researches on urban change detection. For one hand, the 
changes on the ground are analyzed by using kinds of remote 
sensing images. For example, the expanding of cities, the 
changes of land cover and land use, and so on(Li et al. 2005; 
Hassiba and Youcef 2006; Song et al. 2006; Di et al. 2008). It 
has the vital practical significance to urban sustainable 
development Wang et al. 2006). On the other hand, the changes 
of some specific features (for example buildings, roads and so 
on) are detected according to the aerial images, orthographic 
map, and other GIS data(Liu et al. 2002; Zhang et al. 2005). It 
can provide the basis of planning timely and effectively for the 
decision-maker. And this plays a vital role in urban planning, 
construction management and economic development(Liu et al. 
2002). Therefore, how to obtain the urban change information 
accurately appears quite urgent. 
This paper focuses on the changes of buildings in urban. 
Vertical edges of buildings are extracted in pairs of aerial 
images, taking advantage of the character that the vertical edges 
intersect at their vanishing point without fail. Then, the ground 
coordinates of the vertices on each vertical edge are calculated 
according to the projection difference and the principle of 
frontage intersection. Finally, the changes of buildings are 
obtained by carrying on the alternating change analysis using 
these coordinates and the three dimensional city models. 2 
2. VERTICAL LINES EXTRACTING 
Vertical edges are the necessary characteristic of 
buildings(Tang et al. 2004). They have important significance 
to building’s description because they can supply both the 
building’s positional information and the elevation information. 
In the aerial images, the buildings’ vertical edges are mainly 
consisted in the straight lines which are extracted from the edge 
information. According to the knowledge of photogrammetry, it 
is known that vertical edges of buildings are a group of parallels 
which are vertical to the horizontal plane, and intersect at the 
vanishing point. Moreover, aerial images are got by the way of 
central projection, and camera’s lens is the centre of projection. 
In the photographic moment, the camera’s main axis is vertical 
to the horizontal plane approximately (inclination angle of 
images are smaller than 3 degrees(Li et al. 2001)). As a result, 
the principal point can be regarded as the vanishing point(Tang 
et al. 2004), and the vertical edges can be detected according to 
examining whether the straight lines extracted in aerial images 
pass through the principal point. 
Suppose that point O is the principal point of an aerial image, 
line 1 is a straight line detected in the image, and line 1 locates at 
the image block P. The right bottom comer of image block P is 
at (x ; , _y,) , and the left top comer is at (x 2 ,y 2 ) ■ P locates at the 
first quadrant which is shown in Figure 1 (the cases of image 
block P locates at other quadrants are similar to this). 
y 1 
k 
(-v>\) 
/ 
/ 
/ 
/ 
/ 
/ 
/ 
/ 
/ 
/ 
 
p 
/ ✓ 
/ y 
/ / 
(-W.) 
o 
Figure 1 The restriction of vertical edges 
Suppose that k is the slope of a vertical edge. Then the scope of 
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