103
Fig. 3 - Spatial view of the graphic stereoplotting of
the vault architectural structure.
tolerances only with medium and large format (from
6x7cm to 13x18cm) non-metric cameras. The
mounted lenses must be of high optical quality (not
always available in low cost systems) and
furthermore the digital acquisition systems of
photographic images (drum and flatbed scanners)
must be of high optical and radiometric resolution
(>1000 dpi, density range >3,2D). Negative, and
wide tonal gamma b&w films, have been exposed
with a UMK 10/1318 metric camera, equipped with a
wide-angle lens; In many cases settling was made
leaning the camera directly on the floor in order to
have enough distance from the object. The frame
scale was always limited to the value of 1:80*1:100
to have the opportunity to plot till 1:20 scale with
accuracy of 1-5-2 mm.
The difficulties met during the measurement of
control points have been essentially:
• the impossibility of executing measures in
spherical coordinates (angles and distances)
for the impossibility in the prism positioning;
• the use of small value vertical angles with the
consequent difficult collimation and errors due
to the non verticality of the teodolite primary
axis;
• the necessity to collimate only photographic
points (without targets) on architectural
elements with repetitive texture as that of stone
ashlars of masonry vaults, with the consequent
possibility of gross-errors.
Some of the mentioned problems could have been
avoided with the use of no-prism Total-Stations,
which were not available at that time and that seem
to be the only instruments capable to speed up the
leaning operations in such critical condition.
The vector plotting operations have been carried
out in a classic analytical instrument Siscam
Digicart (equipped with 2 pm encoders and 5*18X
zoom lenses). The operation, carried out by an
expert operator, required few plotting hours, being
the photographic images of high quality and with a
sufficiently schematic reading of the masonry
texture. The digital plotting phases aim, instead,
Fig. 4 - Isometric view of D.E.M. generated by
automatic image matching.