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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