International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B5. Istanbul 2004 
well as the detail identification capacity of photogrammetry. 
Consequently, the mesh is decimated in a way to maintain a 
large number of triangles on edges and to reduce the number 
of triangles on flat surfaces. 
Out of this mesh and the undistorted pictures that cover the 
area of interest one can now easily generate orthophotos, in a 
far quicker way then by traditional methods. The so called Z- 
orthophoto (zop-format) as a 2,5D interpretation of the data — 
each point contains depth information — is ready for 
exportation into different CAD programs, eg 
www.ScanDig3D.com , for further post processing. 
A full exploitation of the 3D information of the data set is the 
mono plot procedure, possible through PHIDIAS, a software 
plugin programmed for MicroStation. This evaluation system 
  
provides all the necessary photogrammetric tools for the 
combined evaluation, while being able to display the 
photograph and the scanned data point cloud simultaneously, 
one on top of the other. The basis of a combined evaluation 
of both records is the perspective representation of the scan 
data. Therefore, users can profit from all features of a 3D - 
CAD system when performing an evaluation without having 
to renounce classical photogrammetry. The single frames can 
be co - oriented without consideration of the angles of 
convergence between the pictures. After the definition of a 
drawing surface out of the scan data as plane or triangulated 
mesh, the object can be digitised in the high resolution 
photograph. Figure 4 shows how the drawing of single bricks 
happens immediately in global 3D coordinates, in three 
formats (point cloud, photo and CAD) at once. 
  
  
Figure 4 a) coloured point cloud b) decimated mesh with high resolution texture c) orthophoto d) mono-plot post processing 
3. IMPLEMENTATION 
The crew was split into a scanning-team, a surveying-team, 
and a post processing team working simultaneously in the 
field. 
More than 80 retro-reflecting signals were positioned onto 
strategically important points in and around the protruding 
part of the citadel, the governing place. As these reflectors 
served as tie-points for merging the data of different scan 
positions, their locations were chosen such as to guarantee 
optimal visibility. The description of these points, and 
consequently every measured point , in global UTM 
coordinates was made possible by the results of the surveying 
team who measured the reflectors by dual frequency GPS 
receivers and total station. The signals are automatically 
extracted out of the scan data and fine scanned in a next step. 
Then, by comparing a minimum of six reflectors found in the 
scan data with the pre-established list of global coordinates, 
an automatic matching of the data is carried out, and the 
scanposition is thus registered in the project. All the data is 
used for the hybrid multi station adjustment of the operating 
software RISCANPRO. 
The merging accuracy is displayed instantaneously after the 
automatic finding of the corresponding tie points. The 
feedback of at least six used reflectors with typ. 4 — 7mm 
standard deviation means that the merging process has been 
carried out successfully. The simultaneous display of the 
registered, resampled and merged point clouds of all scan 
positions allows the operator to decide upon following scan 
positions in order to reduce the scan shadows of the final 
scan data to the largest extent. 
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