International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B6. Istanbul 2004
At the relative orientation step it is possible to control the error
of measurements and in such way to change the weights of the
measurements. Simplification of measurement gives the
possibility to “auto locate” the next point after measuring the
initial three points. Simultaneous measurement of image
coordinates in several photographs allows to study the influence
between the measurements of corresponding image points in
cases not only of stereo couple but in the cases of triple,
quadruple or six-fold occurrence of points’ images in the
overlapping photos. The relative influence of tie points, their
disposition and number can be studied by analyses the points
residuals listed in the decreasing order. The outer orientation is
made for whole block of images and requires measurements of
all control points in all images. This causes sometimes
instability of iteration process. To overcome this it is possible to
include photos one after another and to make the calculation
only for photos included in the project. For great pity it is not
possible to deactivate defined photo without removing it from
the project. The influence of control points’ disposition can be
demonstrated by the analyses of error in ground control points
(GCP).
4.2 Orthophoto Generation
The generation of epipolar images is important stage of
processing. This process is executed without definition of any
parameters. But its results are important for the following steps
of processing. Processing of DEM from stereo requires
adequate choice of step of raster grid for DEM. It could not be
very small but must not exceed too much the digitising step of
rectified image. In opposite case the accuracy of model will not
be enough for producing the accurate orthophoto image. The
detailed of model defines the small spikes of the height and
corresponds to the slope of rise or fall of the terrain. The step of
orthophoto generation creates ortophoto of the whole digital
image or for this part of it, for which terrain model exists. Main
parameter that could be controlled is the type of interpolation
function in orthorectification. OrthoEngine allows selection
from several standard methods as nearest neighbour, bi-linear,
cubic interpolations. More sophisticated methods can be
selected too. They are sin(x)/x function for 8 pix and 16 pix
windows, so as the methods based on digital filtering which are
average, median Gaussian and User defined filters. This
versatility allows ‘> make appropriate selection and to make a
comparison between processing speed and accuracy of
interpolation. The possibility for choice of only part of the
image allows the fast test of different methods. Finally the
selected most appropriate method of interpolation can be
applied to the whole image. The mosaicking step allows
selection the method for cutting line selection manual or
automatic and mode of radiometric equalizing between two
merging images in the overlapping zone.
The advantage of usage the PCI Geomatics system is support of
different models for aerial photos, Landsat and SPOTS
scanners, radar images that allows creating DEM and
orthoimages from different aerial or satellite sources. The
processing technique is similar but the used mathematical
models are different that affects the number and position of
ground control points. This can be subject of the training
process.
5. 3-D DIGITIZING
One of the main features of systems for digital photogrammetry
is the digitising in 3-D mode. This feature is important for
50
generation of vector data from digital stereo images. In
education process in UACEG is used DVP of Leica for creating
of Digital vector models of architectural objects, for generation
of DEM from digital aerial images. This feature is important for
generation of vector data from digital stereo photos. The
combination of digital terrain model and vector model of
objects is shown in Figure 2, which is part of diploma thesis of
Theodora Miteva. Terrain modelling was produced by InRoads
of Intergraph (Intergraph, 1995a), which allowed taking into
account the break lines of the model.
ed SS
hes Y
Figure 2. Orthogonal view of the terrain with models of
buildings
The digitising features of PCI OrthoEngine are used for
collection of data for object boundaries and linear features
extraction. The definition of attribute properties for primitive
objects is possible. This allows creating topological description
in GIS environment. The possibilities of ArcView are used for
these purposes. The results of combination between orthophoto
and vector map are shown on Figure 3.
6. DISCUSSIONS AND CONCLUSIONS
The usage of systems for Digital photogrammetry allows
demonstrating the whole technological process of
photogrammetric production on the single or combination of
systems. It is useful for learning of new different system based
on the same principles. Disadvantage of more common purpose
photogrammetric systems is that they are not specially designed
for education and not all processes are visible for students. This
requires developing the special systems, which are designed for
education purposes. Such systems may not to be able to produce
fast the final product, but are more adopted for analysing and
demonstrating of the special features of processing steps and the
most appropriate geometrical conditions and values of source
data and parameters. Examples of such systems are LDIP
(Hóhle, J., 1996) and ARPENTEUR. High interest attracts the
systems that are capable for educational purposes and practical
tasks. The analytical photogrammetric system ORIENT of TU-
Vienna possesses such features. Such versatility can be
achieved if modules of system for digital photogrammetry are
developed as independent modules for example based on
ActiveX modules of Automation model of Microsoft Windows.
The calling procedures can be developed to solve separate
educational tasks or to create full functionally completed
software product, which can be used for solving not only the
educational purposes but for solving the practical tasks. In such
way could be solved some conflicting requirements between
educational and production system.
