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Sharing and cooperation in geo-information technology
Aziz, T. Lukman

Table 1. Comparison the traditional optical/mechanical approach with today’s softcopy AT processes
Process & create diapositives
Not required
Point marking
Solution Robustness
20-30 min
Operator skill dependent
Not required
-60 (user definable)
Superior and consistent
Significant redundancy
The relationship of AT to the aerial survey has also
become very important as GPS
Technology is today being widely applied during air
survey missions. The introduction and success of auto
AT is just starting to be felt, but the implications are
enormous. By minimizing this often difficult and
complex task, the doors to photogrammetry open to a
vast army of potential users, especially as low cost
personal computer systems can now be used for stereo
collection and analysis.
Probably the first successful implementation of
significant automation was in the DTM generation
process. DTM’s are a key requirement for orthophotos
and terrain analysis. When used appropriately auto
DTM generation is now quite successfully applied.
Generally additional geomorphological features such
as break-lines, exclude areas and salient point are
invaluable to the DTM surface formation process and
are highly recommended.
The auto DTM generation process utilizes a features
based matching in a hierarchical process where
refinement via least squares adjustment of the derived
DTM improves as the computation proceeds down
through the pyramids to the lowest level. See Figure 3.
Despite high automation, post process interactive
editing is generally deemed necessary for quality
assurance. The amount of editing and number of
geomorphological features required depends on the
purpose for which the DTM is required. If contours are
desired as final output then detailed collection of break
lines and salient points would be required to give
appropriate structure to the software generate contours.
For orthophoto generation only, often little additional
terrain structure is required.
The process of ortho rectification for aerial
photographs can be summarised as the conversion from
central perspective to orthographic projection. The
conversion is undertaken generally as a batch processes
in which a new output image is generated from the
input image after corrections for terrain height
displacement (requirement for DTM) and photo tip and
tilts (requirement for At) have been applied.
Once images are rectified the step of mosaicking or
digitally joining one or more images may be
undertaken in which several steps may be combined
such as global tonal balance, seam line definition and
area extraction.
Generally it is desirable to minimize the number of
photographs required to “make-up” an orthophoto and
by using good flight planning and GPS camera control
resulting in pinpoint exposures.
Upon completion of the rectification and mosaic
processes the orthophoto image can easily be recorded
(permanently) onto compact disc (CD) for distribution
and archive
There are many challenges ahead, one often talked
about is automatic feature recognition which is still
considered some way away from full and robust
implementation, but like other steps to automation,
incremental advances involving. Research into
automated building extraction is well advanced as with
automatic line following. The challenge is to bring
these research activities into the main stream
commercial systems, which can provide as good if not
better solutions that current interactive techniques
Another area of high interest is at the airborne
acquisition stage where the potential of combing
inertial navigation systems (INS) and GPS could
ultimately result in fully orientated photos at the
moment of capture. Once this technology is refined and
combined with say digital aerial cameras, it may lead
to the elimination of today’s scanning and
aerotriangulation steps.
Small format digital cameras are already being
deployed for aerial imagery capture in conjunction
with GPS recording of exposure stations capturing
either color or color infrared imagery. As the CCD
array sizes expand we can look forward to even more
utilization of these systems with metric or semi-metric