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

analog stereo plotters. This was the “foot-in-door” for
North American software developers in their eventual
takeover of this once European centered industry
The latest phase in the evolution of outomation in
photogrammetry is concentrated around softcopy
systems. Although first introduced commercially in 1991
its only in recent years that significant benefits both
technically and commercially have some to the fore in
distinguishing these come softcopy systems from the
previous generation analytical or optical/mechanical
The introduction of WindowNT R based systems with their
lower cost Intel based host computers and the familiar
graphical user interface (GUI) has been a significant
catalyst in the evolution of softcopy systems in recent
Softcopy has ushered in the dawn of real automation for
photogrammetry. Today we are seeing systems capable of
• unattended scanning of aerial films
• automatic aerotriangulation (autoAT)
• automatic generation of DTM’s (autoDTM)
• automatic mosaicking.
Scanning of photographic films has reached a new stage
of maturity now those roll-feed scanners are
commercially available. The first generation scanners
were essentially designed to scan single sheet
transparencies, which were manually changed and setup.
Roll-feed scanners are capable of unattended scanning,
single pass color, auto dodging and interior orientation.
See Figure 1.
Figure 1.
PhotoScan TD with roll-feed system
Whilst the scanning of photographs may still be
considered a financial impediment to many organizations
wanting to embark on softcopy, a service industry has
sprouted that provides very economical scanning with per
photo costs as low as US$10.00. These service bureaus
have helped significantly in stimulating the market for
softcopy systems.
The industry has progressively adopted TIFF format
image files and although there are many forms of TIFF
including tiled, unfilled, overviews and JPEG compressed
it is now considered a de-facto standard. Most scanners
on the market today can generate TIFF format files
directly or via conversion.
By far the most exciting development to date is the
process of automatic aerotriangulation. This process
forms the basis upon which all-subsequent measurements
and made and has been until now very labor intensive,
prone to error through artificial point marking and
required highly skilled specialists.
The following steps are generally incorporated into the
AutoAT applications :
• Point selection
• Point measurement
• Point transfer along and across strips
• Bundle adjustment
The measurement strategy is based on point clusters
instead of single tie points, then feature based matching
in the first instance followed by least squares refinement.
See Figure 2.
Figure 2.
Automatic aerial triangulation schematic
(Image courtesy of Inpho Cmbh)
The one step that must still be undertaken manually is the
measurement of the ground control points within the
project, this will normally involve a relatively few points.
And anyhow this step is unavoidable regardless of the
methodology chosen.
The following table (Table 1) compares the traditional
optical/mechanical approach with today’s softcopy AT