4. IMPLEMENTATION OF THE TECHNOLOGICAL
PROCESS
In the proposed technology. elaboration of (metric and non-metric)
terrestrial photographs. performed in order to inventory architectural
objects. is implemented in the following stages: determination of
geometric features of the photographs. creation of a model. stereo
digitizing. editing of data, creation of a bodv of the object within the
three-dimensional space.
The ORIENT System is utilised - in the discussed technology - for
determination of geometric properties of a network of photographs.
by means of the independent bundles method. The system allows to
perform a series of plane transformations, determine the elements of
external orientation, the elements of internal orientation (both, for a
group of photographs or for individual photographs). intersections,
resections, to construct a model and to perform its spatial
transformations. Observations in the process of adjustment may be:
fiducial co-ordinates, surveying co-ordinates, pseudo-observations.
as the co-ordinates of ground points of control in the external co-
ordinate system, co-ordinates of points located on geometric models:
parametric conditions may also be considered. Due to these
possibilities of the software it became possible to carry out
investigations aiming at minimising the ground control network and
to utilise surveying observations directly for the geometric
restoration of objects.
The programme has also been used for verification of the created
TERRANET software package.
The TERRANET software package - used for the adjustment of
photographs by means of independent bundles - allows to determine
parameters of internal orientation, additional parameters and, in
particular, parameters of lens distortion (powers 3,5 and 7 of the
polynomial of distortion or coefficients of Torlegard radial distortion
model) and co-ordinates of tie points. Determination of internal
orientation may be performed jointly for all photographs. or
separately. for individual photographs.
It is possible to determine geometric features of 30 photographs.
Elements of orientation may be considered as error-free or as the
elements of known accuracy and - as such - they may be determined.
The algorithm of adjustment is based on the colinearity condition
with additional conditions, direct measurements , such as: horizontal
distances, oblique distances, increments of co-ordinates, horizontal
and vertical angles. All observations are weighted. basing on the a
priori values of mean errors, which are considered as criterion of
identification and elimination of gross errors. The procedure of
adustment allows to calculate the errors of determination of all
determined values. Initial data for the TERRANET package (fiducial
co-ordinates of points being measured) are prepared by means of the
separate TLOWE package, which allows to use several models to
correct systematic errors and to prepare data for other programmes
used for the adjustment. Approximate elements of external
orientation of the entire network of photographs. which are necessary
for initialisation of accurate adjustment, are determined in a module
of generation of initial data of the TERRANET package. The
requirement to utilise this module is to ensure appropriate connection
between photographs and their connection to a control network.
Software used for determination of approximate elements of external
orientation utilises procedures of relative orientation of a pair of
photographs. local. photogrammetric resection or ground resection
and transformation of a local co-ordinate system to a ground co-
ordinate system.
Data collected b» means of the TERRANET routine are used to
reconstruct the model bv means of the MODEL ST routine and the
STECOMETER or the MODEL SP routine and the anal tical stereo
plotter. Algorithm of reconstruction of the model uses the elements
of external and internal orientation and determined parameters of
distortion. In both cases the files which control the stereo digitising
process in the MicroStation system are generated basing on collected
data. The prg ection plane is also defined (it is usually parallel to the
facade); stereo digitizing will be performed in this plane. Retrieved
data are recorded in the external svstem, which is uniform for all
facades of the object. Accuracy of reconstruction of spatial model by
means of the instruments. is. in practice. the verif ing tool of
successful performance of the TERRANET ad ustment routine.
The process of stereo-digitising is preceded by testing the
correctness of reconstruction of a model, basing on differences
on location of a floating mark, obtained as a result of automated
positioning, on the basis of data after adjustment, with respect to
a proper position of a point of a network within the
stereogramme; results of testing are recorded in a protocol.
It is also possible. using the MODEL ST routine, to determine the
geometric features of photographs in the single model mode and to
prepare data for the needs of stereo digitising. in the external system
with known co-ordinates of control points, or in the local system,
related to the object. also with the minimum grid. The control
network mav be created by point co-ordinates, oblique distances,
differences in heights, differences of co-ordinates, azimuths with co-
ordinates of a camera, in the external co-ordinates system. This
solution is mainly applied in the case of utilizing metric photographs.
Resulting parameters are transferred to the MS driver.
In the proposed technology, stereo digitising is performed in the
INTERGRAPH MicroStation system. This system allows to
perform the stereo digitizing in three-dimensional space with the
possibility to separate up to 62 layers of the digitised contents and to
assign separate attributes to particular elements of the drawing
(thickness of lines, types of lines, colours). This allows to separate
elements of different types on the screen, as well as in the data base.
If the stereo digitising process is performed with respect to
reconstruction of the body of the architectural object, it is proposed
to record each facade in a separate, reference file, but in the unified,
external co-ordinate system.
The edges elaborated from various stereogrammes may be matched
directly when the neighbouring. completed facade is read-in. The
elements of drawing should be recorded as closed polvgons. shape
type elements. stream type lines. Outlines of buildings, skeleton lines
and other elements influencing the shape of a body should be
recorded as surfaces. Details and decorations which are not linear
elements. are presented by a stream type line. with parameters of the
quasi-continuous registration. adusted to the scale of object
presentation.
Recording of retrieved data in the stable reference system allows to
simply reconstruct the body of the object during the editing process,
basing on the outline and main skeleton lines, which are recorded on
separate lavers. In the editing process. it is possible to prepare the
series of presentations, which are adjusted to the user's requirements
(as automatic generation of intersections, perspective drawings elc.
covering with raster or an arbitrary hatchure, location of an object
within the selected environment etc. Besides, the numerical inventory
of an object allows to integrate photogrammetric data with designing
data in other CAD svstems.
440
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996
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