The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008 
431 
candidate for matching. In addition, both candidates for 
matching have similar length and orientation related to the 
projected LiDAR straight line 5. Figure 4 also shows that the 
methodology did not find five (26%) correspondences (false 
negatives). All false negative cases are related to either the 
absence of candidates (i.e., the nearby LiDAR straight lines 11 
and 17) or the presence of invalid candidates (i.e., the nearby 
LiDAR straight lines 4, 13, and 15). 
Figure 2. Test building 
Figure 4. Matching result 
Figure 3. Projected LiDAR straight lines 
Figure 3 shows the projected LiDAR straight lines obtained 
through the projection of the 3D roof contour. The resulting 
polygon is relatively close to the building roof edges, as a small 
registration error of about 5-pixel maximum is present. This 
largest registration error occurs with the LiDAR straight line 5. 
However, the LiDAR straight lines 13 and 15 do not aproximate 
correctly the details that are nearby them. 
Figure 4 shows that twenty-four straight lines are extracted by 
the preprocessing steps. The projected straight lines have the 
following number of candidate for matching: ten projected 
straight lines have only one candidate; seven projected straight 
lines have two candidate; and two straight lines have no 
candidates. This result shows that the preprocessing steps filter 
out irrelevant information properly. Straight lines that are 
successfully matched to the projected LiDAR roof contour are 
overlaid in white on the image. The remaining straight lines that 
are rejected by the matching process appear in black. As shown 
in figure 4, the methodology found fourteen (74%) 
correspondences, in which thirteen (69%) are correct and one 
(5%) is incorrect (false positive). Please note that the incorrect 
matching occurred because the matched straight lines is nearer 
to the projected LiDAR straight line 5 than the another 
Figure 5. Completion result 
Figure 5 presents the result of the proposed completion strategy. 
Fourteen projected LiDAR straight lines are replaced by the 
matched straight lines. These straight lines are potentially better 
representations for the corresponding projected LiDAR straight 
lines. The projected LiDAR straight lines 4, 11, 13, 15, and 17 
are kept because they do not have correspondences among the 
straight lines extracted by the preprocessing steps. The refined 
image-space roof contour is determined by using the new 
straight line grouping constructed through the above rules, 
along with the topology of the projected LiDAR roof contour 
polygon. Basically, the new image-space roof contour polygon