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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 
systems. 
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 
years. 
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. 
2. SCANNING 
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. 
3. AEROTRIANGULATION 
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 
processes.