International Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 6. Bandung-lndonesia 1999 
22 
CAT / CAL IN PHOTOGRAMMETRY ON THE INTERNET 
Joachim Hôhle 
Laboratory for Geoinformatics 
Aalborg University 
Fibigerstræde 11, DK 9220 Aalborg 0st, Denmark 
E-mail: jh@i4.auc.dk 
URL: http://www.i4.auc.dk/jh 
Commission VI, Working Group 2 
KEY WORDS: Computer-assisted learning, computer-assisted teaching, digital photogrammetry, automatic measurement, 
correlation, Internet, browser, Java 
ABSTRACT 
CAT/CAL programs which run on any computer and operating system is the dream of many educators. The Java Virtual Machine 
seems to support this ambiteous goal. The reality is something else and many difficulties have to be overcome. The development of 
interactive CAT/CAL programs have to take care of the differences in the platforms and tools. On the other hand the Internet gives 
access to many other ressources and possibilities which will benefit the CAT/CAL programs. This paper discusses the problems in 
development and use of the interactive and Internet-based learning program “LDIPInter”. The topic of “LDIPInter" is automatic 
measurement of images which is a central topic in digital photogrammetry. By means of rolling texts, animations and several tasks 
with changing data sets the learner becomes interested and active and will understand the process of automatic measurements better 
than with text books. Articles, manuals and dictionaries, which are accessable by the Internet, can be used in addition. The 
realisation of good CAT/CAL programs requires many resources, and suggestions are made how an international cooperation could 
improve the situation. 
1. INTRODUCTION 
The Internet can be used as a learning tool in combination 
with other aids. Especially in distance education, the Internet 
will play an important role. By means of the Internet many 
new opportunities will be created which can support the 
learning. For example: 
- search for literature and access to 
complete texts of articles 
- use of encyclopaedia, manuals and 
dictionaries, etc. 
- communication between students and 
teacher as well as between students 
The distribution and use of learning software packages is also 
possible. The learning by means of these software packages 
is often called “Computer-assisted learning" (“CAL”) or 
“Computer assisted teaching” (“CAT”). If the Internet is used 
as the platform for a CAT/CAL program various advantages 
can be found (compare figure 1). Thanks to the Java Virtual 
Maschine (JVM) such CAT/CAL programs are automatically 
installed on many different platforms consisting of computer, 
operating system and browser. This platform independence 
is especially necessary for CAT/CAL programs because 
many different systems exist in educational environments 
around the world. Furthermore, the latest version of such a 
CAT/CAL program can be downloaded from the Internet at 
any time. There exists a wealth of share- and freeware which 
could be integrated into new CAT/CAL programs. The 
development tools (Java compiler, editor, debugger and 
applet viewer) are also freely available which may start a 
common development at different locations. The use of a 
learning program could be monitored (counted) and even 
charged. 
With all these advantages in mind, an existing and 
established CAT/CAL program, “Learning about digital 
photogrammetry” (“LDIP”), was transferred into an Internet 
version, called “LDIPInter”. First experiences from the 
development of this Internet-based CAT/CAL program was 
presented in (Hohle 1997). In the meantime, new themes 
were added and experiences gained from its use at different 
platforms. It is the purpose of this paper to inform about the 
new achievements and about the user experiences with this 
type of CAT/CAL programs. In the following chapter the 
latest version of “LDIPInter” ( 1.14) will briefly be 
explained. 
2. THE CAT/CAL PROGRAM “LDIPInter” 
The Internet-based CAT/CAL program “LDIPInter” explains 
the theory behind automatic measurements in images step by 
step and provides exercises for each step. Currently, it 
contains two themes: “Automatic measurement” and