An Improved Method of Building Rapid 3D Modeling Based on Digital Photogrammetric Technique - Advances in Image and Graphics Technologies - page 177

a recursive depth priority search algorithm is developed to achieve all related lines.
Figure 2 shows the process to extract all the relevant lines related to a seed line
marked as red color.

Fig. 2. The extraction progress of relevant lines

(2) Reconstruct the relevant lines
For the recognition of roof surfaces, the abstracted relevant lines need to be
reconstructed. First of all, the relevant lines are divided into three categories
according to whether they can form roof surfaces directly: decided, involved and
suspended lines. The decided lines can constitute roof surfaces independently, and
also are not utilized by other surfaces. The involved lines also can shape surfaces, but
maybe utilized by other surfaces, i.e. interacting with other relevant lines. The
suspended lines cannot form surfaces itself while may be possible with other lines
together. The red lines in Figure 3a indicate the three line types.
Secondly, the decided lines are extracted directly to build surfaces, while the others
are broken at intersections to form simple line segments. Figure 3b shows the results
of breaking the lines.

a) Three line types b) The results of breaking the lines

Fig. 3. Line types and its reconstruction