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major issues associated with this integration focusing on
aerial imagery, and we will try to evaluate the current state-
of-the-art in photogrammetric research pertaining to it.
2. INTEGRATED PHOTOGEOGRAPHIC
DATABASES
Geographic information systems deal with acquiring,
storing, retrieving, modeling, analyzing and displaying
qualitative and quantitative information on spatially related
data. The involved data are quite diverse, ranging for
example from land use models and scanned maps to DEMs,
and they exist in a variety of types and formats [Ehlers et al.,
1991]. The information conveyed by these data describes
position, topology, and attributes of entities.
Regarding image data, and despite the rather obvious
importance of imagery in describing geographic
information, GIS and image analysis processes can be
currently considered complementary but not yet fully
integrated, with GIS beginning where image analysis ends.
The situation is very effectively described in [Berry, 1995]
where GIS and image analysis are presented as being the
realm of specialists in segregated offices “down the hall and
to the right”. Indeed, in current practice, imagery is
employed as data source for geoinformation extraction
through image analysis methods. The resulting information
is subsequently introduced in a GIS, but the imagery itself is
not functionally incorporated in it, with few notable
exceptions on display-oriented tasks (e.g. display of
georeferenced data overlaid on image data). Thus,
information flow between image analysis and GIS is one-
directional and communication is rather minimal (Fig. 1).
Imagery
eoinformation
LJ] Layers ^)
==
Image
Analysis
GIS
Real
World
Fig. 1: Image Analysis and Geographic Information
Systems: information flow in a non-integrated environment.
With the use of digital imagery, the physical, integration-
prohibiting obstacles caused by the incompatibility of
analog imagery and digital geoinformation are eliminated,
opening the way for full integration. It has to be noted here
that the full integration of digital imagery in a GIS refers not
only to the storage and management of raster image files
within a geoinformation system, but also to the embedding
of image analysis operations within such a system, with
these operations supporting as well as being supported by
relevant existing geographic information. Thus, an
integrated environment is characterized by bi-directional
information flow (Fig. 1), as:
25
25
e geoinformation produced through image analysis
operations is introduced into the GIS (similarly as
before), but furthermore
e existing geoinformation can be used to support image
analysis operations, and
e the images themselves are introduced in the GIS, with
their management and operations supported by the
integrated database environment, and supporting
relevant GIS tasks.
The term photogeographic is used in this paper to refer to
such an integrated environment, to emphasize the role of
imagery within it. An integrated photogeographic
environment allows the optimal exploitation of the
interrelationships which exist among different databases.
These interrelationships are spatial, resulting from overlaps
in the object space, and temporal, existing when various
databases express the state of the object space at different
time instances. This is obviously the case when
multitemporal imagery is involved, or is even the norm
when imagery is integrated with data collected through other
methodologies.
Imagery
Geoinformatio
Analysis
Real
World
Fig. 2: linformation flow in an integrated
photogeographic environment.
The full exploitation of an integrated photogeographic
environment allows digital photogrammetry to become a
key component within GIS, with a role surpassing its current
as data input method.
3. PERTINENT PHOTOGRAMMETRIC
ADVANCEMENTS
Among the substantial photogrammetric advancements of
the last 15 years, the advancements in research topics which
deal with image orientations, DTM and orthophoto
generation, and object geoinformation extraction are the
ones which are most affecting the move towards integrated
photogeographic information environments, supported by
the developments in softcopy workstations. The special
value of these issues for integration lies mainly on their
fundamental role for geopositioning an image and the
information extracted from it.
3.1 Orientations and Aerotriangulation
Orientations and aerotriangulation are essential as they
permit the positioning of imagery in space, and
subsequently, the introduction of this imagery and
information extracted from it in a GIS. Automation in these
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996
