A Top-down Approach to Interactive 3-D Modelling of Architectural sites 
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modelled object. If the primitive is also visible in another image which relative orientation is known, it can be slid inside its viewing 
pyramid until the matching is obtained in the additional view. This particular mode proved very convenient for robotics applications. 
a) optional selection of a reference system and first view exterior orientation 
b) acquisition of a first model 
c) exterior orientation of the next view wrt the model in process 
d) model completion with new primitives 
Fig. 2: Flow chart of Pyramide interactive 3-D modelling principle 
Image or local coordinate systems are used to control primitive positions with the mouse. In order to make this work intuitive, 
primitive motions are linked to cursor motions. Inherently no more than two parameters may be controlled simultaneously using a 
mouse. This restriction is not awkward: less degrees of freedom have to be controlled and less difficult is the fine matching. Besides, 
unused operators often prefer axis after axis control. On the other hand, only a rough solution can be manually obtained using a 6-dof 
input device, and very efficient automatic attraction procedures towards image features are required to obtain a fine matching. 
Actually the key problem using a simple mouse deals with the estimation of the object orientation when the rotation axis is unknown. 
Solutions are given in the following. 
Within Pyramide system, modelling and resetting tasks are managed as distinct activities. Modelling refers to the modifications 
applied to the 3-D model such as primitives’ insertion or deletion, control of their position and shape parameters, their assembly or 
separation, edition of their attributes (name, colour, material, local reference, ...). Resetting refers to the matching of rigid objects 
with image features. This task may be performed indifferently to move a single object, a group of objects, the whole model, but also 
the image viewpoint (exterior orientation) or even the robot in the case of an on-board camera. Although the result is quite different, 
the work is identical from the operator's point of view. Modelling and resetting workshops are proposed to handle each activity 
through a dedicated interface. More recently specialized modelling workshops have been added in order to provide an optimised 
interface to model specific environments, such as piping elements, taking into account dedicated primitives and assembly constraints 
(Even, Fournier and Gelin 2000).