4. EXPERIMENTAL RESULTS AND DISCUSSION 
4.1 Experimental Results 
The experiments have been performed using actual high 
resolution satellite imagery and experimental maps. The 
experimental area is located in Hamamatsu city, a residential 
area in Shizuoka Pref., Japan. The satellite imagery is 
panchromatic QuickBird imagery (geometrically corrected 
0.7m resolution). The map is digitized manually. 
Approximately 5% (23 of 490) of building polygons in the map 
are removed randomly to evaluate the newly-built building 
extraction accuracy. The result is shown in Figure 9 and 
indicates that the changes of small buildings (i.e. 10m wide) 
could be detected while using high resolution satellite imagery 
which spatial resolution is relatively low compared with that of 
aerial photography, especially in dense urban contexts. 
4.2 Discussions 
4.2.1 Overall accuracy: Table 2 shows building detection 
accuracy. The meaning of "changed" buildings includes 
"demolished" and "need to re-examine" buildings. 
go 0 
| Xe UU 
oo oo cng 
Sha 5 
Ban 
  
For existing and changed buildings, the detection rate was 
approximately 89%. About half of the 54 misdetections were 
caused by digitizing errors of the experimental map figures 
(they looked almost changed). This result suggests that even a 
possibility of a small change can be detected by this method. 
Misdetections were caused by buildings with highly dark 
colored roof or very complex roof structure (i.e. half-hipped 
roof, monitor roof). Meanwhile, there were a few misdetections 
of buildings with simple flat roof. The results indicate the 
efficiency of the optimal boundary extraction with the 
acceptable position error and various types of buildings. 
Furthermore, the ability of extracting buildings with weak 
edges by similar materials of roof and background, and partly 
occluded by trees are confirmed. For newly-built buildings, the 
detection rate was approximately 83%. Misdetections were 
caused by buildings located too closely to other buildings so 
that the region segmentation process failed, and colored too 
dark to see even with human eyes. False detections were 
caused by only cars and vegetation. The results indicate that 
the complex buildings consisting of multiple roof surfaces with 
bright or dark colored, or its combination, were extracted 
efficiently. 
Figure 9. Experimental result of building change detection. (a)QuickBird satellite imagery (Hamamatsu city, Japan). 
(b)Experimental map (buildings, parcels). (c)Overlaid imagery and map. (d)Detected results. (e)Changed and newly-built 
buildings. (f)Updated map. (yellow=existing, red=demolished, blue=newly-built, green=need to re-examine) 
74 
Ex 
Ch 
Ne 
Ta 
anc 
anc 
bui 
the 
bui 
bui 
bui 
the 
the 
bui 
Ope 
Wa: 
tho 
tho 
det 
The 
me 
det 
val: 
ser 
reci 
loc: 
bui 
Exi: 
Cha 
Tat