International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B5. Istanbul 2004
photographic tripod to avoid moved photos, or in its
defect to make the shots with the camera supported
on some stable element; it will be preferable to make
the shots with elevated values of depth of field,
because we will not run the risk of defocusings; each
element to represent must be content in a minimum of
three photograms; the convergence between
photograms taken from different positions must have
optimal values of 90° and good values of 60° so that
the adjustment of beams is made in good conditions;
whenever it is possible, a perpendicular shot to the
face of the object to photograph will be made; the
overlaps between photograms will have to be of 50%
at least; the shots will have to be made of such form
that the element covers most of the photogram
surface.
In Figure 1, two examples of photographic shots are shown; a
general shot and a detailed shot. In the right image, z axis
direction defined by the plumb line is indicated.
Figure 1. Example of the photographic shots. In the second
image, z axis direction defined by the plumb line can be seen
2.1.2. Laboratory work: Once field work has been finalised,
laboratory work begins, proceeding with the analysis and
processing of the information collected. With this information
saved and classified two different alternatives are considered: the
information can either be filed away until the need arises to
process it, or it can be immediately processed, resulting in 3D
models of the original structure. In order to reach this objective
it will be necessary to resort to the photogrammetric stations.
Due to the characteristics and aims of this work, the use of
Digital Monoscopic Photogrametric Systems are recommended.
A series of successive steps will be carried out when processing
this data, as is briefly stated below:
gs Orientation of the Photograms. In this process the
position of the shots is calculated. In Figure 2, you
can see different positions of the photographic shots
we have made.
ææ Levelling and forming the scale of the model. From the
direction defined by the plumb lines, z axis is
established and so the model will be levelled. The scale
is attained from the distances measured on the plumb
lines.
ææ Restoring of points, lines, polylines or other
interesting graphic sources, thus obtaining numerical
values, measurement and 2D and/or 3D models (wire
models, surfaces models, textures models, etc).
ææ The three-dimensional models generated are now able
to be exported into conventional formats (dxf, dxb,
vrml, etc.)or to other programs for their display and/or
processing treatment.
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Figure 2. Positions of the different photographic shots
calculated in the orientation process
3. RESULTS
3.1 Numerical results
In table 1 the theoretic results obtained can be seen when the
process of orientation was carried out on a “Photomodeler Pro
4.0"digital photogrametric station. The shots were taken with a
“Kodak Dx3500" digital camera, exclusively using plumb lines
on which the distances were previously marked for the
orientation, scale and to obtain the model geometry. The results
viewed provide information on the quality of the process of
orientation and indicate: an average of 95% of the accuracy of
the points and the quadratic composition of the averages; the
average quadratic error, the average error and the maximum error
in metres observed in the parallax; standard deviation in pixels
and maximum value of the residues observed for one point.
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