Second, one can choose to extract edges and corners and associate them to a part of the building model. For example, a roof-side of the building can be specified by an edge extracted in the image. Then this edge is added to the current hypothesis. (see also Example 3) Our systems are implemented to run under the RCDE. This environment allows the use of mouse-sensitive features thus facilitating user selection and manipulation of features.
After each corrective interaction the system forms a new parallelogram-hypothesis, the system looks for new edges, shadow and wall evidence to support the new hypothesis and finally performs a fitting and verification step. These methods are the same as those in the automatic system. This important step of verifying the consistence to the constraints proposed in the USC-MABS can be compared to a fitting process in a computer assisted manual systems, though in our system a fitting is performed after each interaction. Therefore it is possible that, after a manual correction of a roof-boundary, the wrong building height is also corrected automatically.
Without the fitting step the system would perform like a manual system and at least three interaction steps (two corner adjustments and one correction of the building height) would be necessary for adjusting the shape of one building model. Rotation and translation as parameters of the position add another two steps.
Note, that the manual feature extraction and the following fitting and verification steps can also be applied to buildings that are automatically detected, but partially wrong.