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PC-TAS: PC-TOOLED ANALYTICAL STEREO-MODELLING
Jonas Nelson, Research Engineer
Dept. of Geodesy and Photogrammetry
The Royal Institute of Technology
SWEDEN
Commission VI, Working Group 2
KEY WORDS: Analytical, Photogrammetry, Digitization, Education, Software, Computer Assisted Teaching
ABSTRACT:
A basic understanding of the principles of analytical photogrammetry is commonly regarded as essential for every
student in the photogrammetric area. However, analytical stereoplotters are quite expensive, they require a certain
space, and there can only be one operator working at the same time. Normally, a university or institute does not have
access to more than a few analytical stereoplotters, while the students may be numerous - especially in the earlier
courses.
The Department of Geodesy and Photogrammetry at the Royal Institute of Technology, Stockholm, Sweden, has
developed an educational aid in this field, called PC-TAS (PC-Tooled Analytical Stereo-modelling). PC-TAS is a
concept which uses simple hardware and software available at almost any university: A cheap digitising table and an
ordinary PC with MS Windows, MS Excel 5.0 (or higher) and Software Wedge (a TAL Enterprises software for linking
the digitising table output to the Excel sheet. Similar softwares may be equally good to serve this linking purpose).
However, the real tool in the PC-TAS concept is the 350 kb Excel sheet where all input, calculations and output are
done.
With this relatively simple and inexpensive equipment the students can sit down at the PCs and explore the basic
principles of analytical photogrammetry in their own pace and with their own hands. The number of exercises on the
analytical stereoplotter can be reduced drastically (normally there are more PCs and digitising tables available than
there are stereoplotters). In addition, the PC-TAS Excel sheet is designed for beginners and is easy to use with its
different colour codes indicating where to digitise and where to look for different kinds of results.
1. THE DEVELOPMENT OF PC-TAS the time for program development was sparse and it
would be easier to use an existing software than to
develop a new one. Another important factor was that
the students were already familiar with this software from
Faced with the fact that 100 students were to be given a other applications. It is also an advantage that it is fairly
basic course in photogrammetry, the Department of easy to get an overview of the calculations on an Excel
Geodesy and Photogrammetry at the Royal Institute of — sheet, to see how the equations are built up and to trace
Technology realised that a single analytical stereoplotter the dependants of a variable.
would not be sufficient for their needs. The thought of
developing an easy-to-use analytical software for
educational purposes arose.
It should be noted that the idea of using a digitising table 2.1 Hardware requirements
together with some software for analytical photo-
grammetry is not new - there have been commercial PC-TAS uses an ordinary PC capable of running MS
Systems available since 1983 at the very least. (WB —— Windows 3.1 and MS Excel 5.0 (or higher versions).
Geomap and Leica, to mention a few). Those systems You will also need a digitising table which is possible to
perform well, but they have a minor drawback: the connect to the computer. The digitising table could be of
software can only handle a certain type of input data, any make, as long as it is capable of transmitting output
restricting the number of possible digitising tables. PC- data (x and y coordinates) in a single output string. A
TAS uses Software Wedge (from TAL Enterprises) as a high resolution table is preferable, but not necessary.
link and "interpreter" between the digitising table and MS
Excel. It is easy to change the configuration to suit 2.2 Software requirements
almost any kind of digitising table.
1.1 Background
2. THE PARTS OF PC-TAS
Apart from the PC-TAS 350 kb Excel sheet, you will
need MS Windows 3.1 (or higher versions), MS Excel
5.0 (or higher) and some software to analyse and link the
There were several reasons behind the decision to use digitising table output data to MS Excel. We use
Microsoft Excel in the PC-TAS concept. Most important,
1.2 Why using Microsoft Excel?
111
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B6. Vienna 1996