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Figure 2 - Orthoproiection of the image digitized at 300 dpi, processed without using breaklines. 
the zoom of a detail. Figure 3 shows the orthoprojection of 
an image digitized at 2000 dpi and processed with the help 
of breaklines, with a zoom on a detail with the same 
degree of enlargement as the previous. The differences 
are beginning to become clear. 
On the other hand, the two photographs of the attic have 
been rectified with 4 control points each. Successively, one 
has assembled a mosaic of each photograph with the rest 
of the view, without equalisation of the images and 
without softening the chromatic junctions. Figure 4 shows 
all three operations (rectified photos and two 
orthoprojections) superimposed on the known vector data, 
derived from the surveyed cross section and from the 
geometric lines obtained by photogrammetric plotting. 
From an analysis of the residuals on signalized points, 
both on the orthophotos and the rectified images, values 
are found in the order of 5 mm. 
The procedure has a high degree of automation. The 
memory requirements become important. The file of the 
generated combination has a size of about 15 Mb. 
From the figure one can already see how the attic images 
(printed three times enlarged and digitized at 300 dpi) 
have characteristics, which are more than sufficient for a 
series of possible applications. Not sufficient however is 
the digitizing at 300 dpi of the negative of the 
orthoprojected photograph. Excellent and maybe 
exuberant in definition is the resolution of the photograph 
read at 2000 dpi. 
2.5 Metric considerations 
One must remind first of all that, in orthoprojections, each 
pixel maintains the three dimensional characteristics of 
the object, while in rectified images, which obviously are 
two dimensional, one looses the information with respect 
to depth. 
  
Figure 3 - Orthoproiection of the image digitized at 2000 dpi, processed with the help of breaklines.