Figure 1: A CAT/CAL program on the Internet gives access to resources and allows for 
communication 
“Correlation in the subpixel range”. One more theme, 
“Correlation in the subpixel range - two dimensions”, is in 
preparation. The explanation of the theories is supported by 
animations, sequences of text lines, and hypertexts (compare 
figures 2 and 3). 
The exercises are mainly calculation tasks with different data 
sets. “LDIPlnter” features a high degree of interactivity which 
puts the students in an active role. The program analyses the 
results given by the student and answers “Correct” or “Wrong”. 
The formulae can be displayed in information windows; they 
contain matrices and Greek letters. The student manipulates a 
graph and reads values from the graph and uses them in the 
calculations. For the rather complicated calculations a 
calculator and a spreadsheet are available. Their use is 
explained in help windows. More detailed explanation 
concerning the use of the spread sheet or the theoretical 
background of the automatic measurement can be downloaded 
from the net. 
“LDIPinter” is installed on a server at Aalborg University under 
the address; 
http://sunsite.auc.dk/LDIPInter 
and can be transferred and used by means of an Internet 
browser. 
For the proper run of “LDIPlnter” it is important that the 
Internet browser includes a Java bytecode (applet) interpreter. 
3. DEVELOPMENT OF LDIPinter 
The contents of the learning package “LDIP” existed in a 
previous version made for Macintosh computers (Hohle, 1996). 
The programming language was PASCAL, and the 
development task for “LDIPinter” consisted mainly in 
transferring the PASCAL code into Java code. However, some 
of the PASCAL toolboxes did not exist in the Java Application 
Programming Interface (API) so that part of the program had to 
be done from scratch. Furthermore, the experience gained with 
the behaviour of the different platforms resulted also in new 
ways to program. The applied tools (compiler, editor, debugger 
and applet viewer) are contained in Sun’s Java Development 
Kit (JDK) which can be downloaded free of charge from the 
Web. The applied version was JDK-1.1.5, and the same main 
version (JDK-1.1) has to be used by the producers of the applet 
interpreter which is then part of the browser. If this condition is 
not fulfilled, problems may occur when running “LDIPinter”. 
In order to fulfil the ambitious goal of “platform 
independence” for “LDIPinter” various tests had to be carried