An Improved Method of Building Rapid 3D Modeling Based on Digital Photogrammetric Technique - Advances in Image and Graphics Technologies - page 179

a) The separated solid models b) The reconstruction of solid models

Fig. 5. The creation and reconstruction of building solid models

2.4 Reconstruct Building Solid Models

The reconstructing process combines the separated solid models into a complete one.
To the complicated buildings, solid union operation usually can't receive right results,
and some more combining rules need to be designed. The following is the rules gotten
by analyzing the different building structures.
Firstly, all solid models of a building are sorted by the top elevation in descending
order. The later combining operations will be fulfilled according to that order.
Secondly, the following rules are taken when combining two solid models, which
are formulated based on the interference (intersection) relationship of them:
(1) Union the two models when they interfere but don't contain.
(2) The model with higher top elevation subtracts the other one when they interfere
and contain.
An example is shown in the figure 5b. In the five solid models, three pairs interfere
but don't contain, i.e. (a, c), (a, d) and (a, e), and two pairs interfere and contain, i.e.
(a, c) and (a, e).
By the above rules, the building solid models are created completely. After that,
the bottom surfaces need to be deleted for the building models are usually placed onto
a landscape layer composed of DEM and DOM.