The orthophoto projection program resolves with 
practically identical residuals at the control points both 
the photograph digitized at 300 dpi and that of 2000 dpi. 
Much more evident, from the metric point of view, are the 
effects of using or not using breaklines; it is not possible to 
consider not using them and rather the previously 
discussed problems, regarding their generation in 
architectural photogrammetry would deserve a more 
profound study to find a suitable solution for the general 
case of an arbitrary viewing condition and an arbitrary 
object. 
The metric characteristics remain however correlated 
according. to the normal photogrammetric logic, to the 
mean scale of the photograph, the focal length of the 
camera, the size of the photograph and on the baselength 
of the stereo copy. Considering the memory requirement 
problems with digital imagery, obtained by scanning at 
2000 dpi, and the their esuberance in definition, one has 
to ask oneself wether it would not be more convenient to 
work with a smaller scale, with respect to those used in 
the survey, for the processing of photographs with the 
previously decribed raster analysis. This consideration 
becomes more realistic when the deformations, introduced 
after the photograph was taken, are corrected with the 
help of the grid of crosses included in the camera. The 
subject deserves a systematic study in close correlation 
with the characteristics of the available hardware and 
software. 
At this point it may be appropriate to make the following 
consideration. The level of scanning necessary in order to 
be able to define the used metric pixel for example for 
autocorrelation of images is esuberant if the metric 
characteristics are guaranteed by the D.T.M. and the pixel 
is only used to transform the qualitative information of the 
photograph. 
2.6 The plots 
In our opinion, the stage of output on plotter is the part, 
where the limits of the current hardware are met and 
where (which is equivalent) costs are a major factor. 
The first large limitation is the number of different grey 
levels, which are reproduced in the plotting stage. This 
number is at least four times smaller than the 256 grey 
levels obtained during digitizing, even when using a 
thermic printer. This characteristic is very selective in the 
field of architecture where the contours of the object are 
only a part of the final result. Results of sufficient quality 
(with respect to traditional orthophotos and rectifications) 
Figure 4 - Rectifed photos and orthoproiections superimposed on the known vector data. 
using an Iris Inkjet 6024. j 
Anyway, for output on paper, the number of grey levels in 
plotting has a larger influence on the result than the 
resolution in scanning. In fact, even the printing of an area 
scanned at 2000 dpi has characteristics, which make it 
unacceptable with respect to normal products of typical 
working products of the architectural environment. 
2.7 Conclusions 
Because of the rapid developments of hardware and 
software, even an expert is at the mercy of the market of 
informatics and every statement can be outdated in a short 
time. 
This is however not the reason, which urges us to state 
that elaborations obtained from scanned photographs and 
successively orthoprojected and rectified with overlaying 
of vector data can be extremely useful to architecture. 
In our opinion, the most important result of the present 
research is, at least for the moment ????, The weak part 
of the three dimensional processing of images remains the 
output on paper, also from the point of view of metric 
precision. 
It could therefore be intelligent to have a different 
relation with the user of a photogrammetric survey. One 
does not have to supply a plot, but, once familiar with its 
use, provide a computer based copy of the orthoprojection 
and / or the rectification, which is easy to manipulate with 
software. The user can then take advantage of the 
characteristics of digital images and elaborate grey levels; 
he can equalize the images; he can carry out ad hoc vector 
based operations and possibly print them on paper, 
without running into problems in connection with plotter 
characteristics, having only to print only lines and hatched 
areas. An example can be the following: an art historian, 
using the result of an orthoprojection of a wall of bricks, 
wants to study the stucture of the wall. Once the grey 
values corresponding to the fugues between the bricks 
have been identified, the fugues can be highlighted and 
the intensity of the other grey valuescan simultaneously be 
lowered. On the video screen appears only the fugue 
structure. By entering in editing in these conditions, he can 
create a vector based drawing on a suitable layer, which 
can be processed separately and which maintains the 
metric quality of the orthoprojection. 
From this point of view, an experiment is being carried out 
with a restorer of a fresco of the Zavattari's in the Chapel 
of Queen Teodolinda in Monza's Cathedral, to verify the 
applicability of  photogrammetry to the field of 
architecture.