Drap, Pierre 
  
In each architectural entity there is a block managers object in charge of managing blocks. It is possible to obtain a lot 
of data from each single block : 
Owner : the architectural entity. 
Model : the photogrammetric model used for survey. 
Plane : the plane used for extrude (including measured points to compute the plane). 
Measured points . 
Computed points (after the extrude phase). 
Extrude depth : measured or defined by the archaeologist. 
Y V V V WN NV 
Access to the polyhedron of morphology representation. 
All these data are available from each ashlar block or from a Block-Manager object in charge of managing all the 
entity 3 blocks, or also from a general Block-Manager. The Block-Manager is also in charge of ranking blocks (finding 
adjacent or neighboring objects according to special criteria), calculating statistics (on volume and dimensions). 
3.3 Measuring the blocs 
As often as possible we try to compute the 
complete geometry of a block during the survey 
process. The measurement can be done, and has 
in fact been done by an archaeologist, the most 
important point at this step being not a high 
competence in photogrammetry (the correlation 
process help a photogrammetrist neophyte to 
determine the homologous points) (Drap P., 
Grussenmeyer, P., 1998), but the integration of 
architectural knowledge into the model. 
  
During the survey process the operator informs 
the system on which kind of ashlar block he is 
measuring, its third dimension, the architectural 
entity it belongs to ; he chooses the points used to 
compute the extrude plane and decides or not to 
use the bn the fly'extrude facilities. 
  
  
  
The depth can be determined in two ways : 
Figure 2. The survey process in Arpenteur. 
If, as generally, only one face is visible, the depth 
is evaluated by the archaeologist according to properties known from the monument itself. At Aleyrac, the dismantled 
walls give an insight into the inner structure of the masonry and the dimensions of ashlar blocks of the facing. These 
actually differ from course to course, in order to create a firmer link with the stones and mortar filling the space 
between the two facings. In the specific case of certain cornerstones or voussoirs the third dimension can be deduced 
from the other apparent face or faces. 
4 CALCULATION OF INTRINSIC PARAMETERS: THE CASE OF AN ARCH 
In the present case the aim is to determine the geometric definition parameters of each architectural entity using both the 
measured blocks and the architectural knowledge (the geometrical definition of the entity morphology, structural and 
building knowledge). 
For each architectural entity it is possible to isolate a set of relevant blocks giving some information on the geometric 
parameters. This approach requires three steps : 
> The determination of the object’ bounding box and of its own referential. 
> The isolation, according to geometrical and topological data, of several sets of blocks for each geometrical 
parameter to compute. 
> Finally isolating points (held by the blocks) and computing by least square adjustment the geometric parameters of 
the entity. 
As specified above, we present here the case of the north transept arch. 
  
190 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B5. Amsterdam 2000. 
  
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