Computer-assisted teaching and learning in photogrammetry

ELSEVIER ISPRS Journal of Photogrammetry & Remote Sensing 52 (1997) 266-276

PHOTOGRAMMETRY & REMOTE SENSING

Computer-assisted teaching and learning in photogrammetry

J o a c h i m H6h le *

Aalborg University, Department of Development and Planning, Fibigerstraede 11, DK-9220 Aalborg, Denmark

Received 19 April 1997; accepted 17 June 1997

Abstract

The advanced personal computer models, new storage media such as CD-ROMs, new authoring tools and especially the Internet will influence the production of learning software for photogrammetry. Some examples of learning programs are presented, including experience from the development and use of these programs in the education of land surveyors. They demonstrate the progress made over the years as well as the potential and possibilities of computer-assisted teaching and learning in photogrammetry.

Keywords: computer-assisted teaching; computer-assisted learning; teachware; digital photogranunetry; image processing

1. Introduction

Photogrammetry has changed considerably during recent years. The photographs taken can be digitized by means of scanners, or digital imagery is taken by digital cameras. The reconstruction of the object is carried out by means of the computer only. When using digital imagery, the measuring process can be automated partially. However, the computer- based evaluation systems are rather sophisticated and the amount of data to be processed is usually huge (approximately 100 Mb per aerial image). This means that these systems are expensive, and they also change quickly. Education in photogrammetry at university level can neither afford all of the latest imaging and image evaluation systems nor have it in considerable numbers for the training of a large number of students. This is where computer-assisted teaching and learning (CAT/CAL) comes into focus.

E-mail: [email protected]; URL: http://www.i4.auc.dk/jh

The computer is used together with a CAT/CAL program as a learning aid (see Fig. 1).

The equal treatment of students, their active role in the learning process and the general fascination of working with computers are some of the reasons that CAT/CAL gains in popularity. Also, mass education, distance learning and self-study are good reasons to apply CAT/CAL. A quick response to questions or tasks is essential in this type of education. CAT/CAL in photogrammetry has been used at Aalborg University since 1987 and various programs for personal computers (PCs) have been developed and used in the education of land surveyors (Dres- ling et al., 1988; H6hle, 1992). The arrival of the Internet may change the education further and first experiences with CAT/CAL programs on the Internet are encouraging (H6hle and H6hle, 1996). It is the main purpose of this article to present the potential and possibilities of CAT/CAL in photogrammetry.

0924-2716/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. Pl lS0924-2716(97 )00022-1

J. H6hle / ISPRS Journal of Photogrammetry & Remote Sensing 52 (1997) 266-276 267

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Fig. 1. Learning aids.

2. CAT/CAL programs for photogrammetry in general

Computers have been used in photogrammetry since the 1950s. Large computational tasks, where many unknowns had to be solved in least square adjustment, had to be carried out. Program packages for the determination of orientation parameters of photographs were rather sophisticated and therefore very expensive. These programs were 'closed' which means that the source code was not available or could not be understood by people other than the developers themselves. The same applies to the programs for terrain modelling, which are also part of the education in photogrammetry. Computers and software were also integrated into the evaluation equipment. They replaced a large number of mechanical parts and assisted the operator in the orientation of the stereo pair and in the plotting and data collection. Furthermore, the servo-driven measuring machines (analytical plotters) are again very

expensive 'black boxes'. Finally, the transition to digital imagery showed the same pattern: the evaluation systems are either complex and rather expensive or too simple, having no automated measuring facil- ities. The education, however, can go another way and use or supplement computer-assisted teaching and learning. CAT/CAL means that the computer and software are used and pedagogical principles are applied. Using pedagogical principles requires that: • knowledge is presented in smaller units, from

easy ones to more difficult ones; • questions and exercises are attached; • the answers to questions are analyzed so that

students get immediate response; • fun and play are integrated; • the student can determine the speed and the place

of learning; • success and progress can be experienced.

Furthermore, special features of the computers can be used with advantage in CAT/CAL. For example, various media such as text, graphics, sound,

268 J. H6hle / ISPRS Journal of Photogrammetry & Remote Sensing 52 (1997) 266-276

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0 0 0 Fig. 2. Work room for computer-assisted teaching and learning. Ten PCs are connected via a network, so that CAT/CAL programs and data can be downloaded from a large disc. The teacher's computer is connected to a colour projector (RGB) so that the content of his/her computer screen is duplicated and projected to a large screen. All of the students (here represented by a circle) can follow the teacher's demonstration.

images, etc. can be integrated and combined. Dy- namic pictures and animation can be created. On the other hand, PCs are today low priced and they will become even cheaper and better in future due to the heavy competition between the producers. This means that the students can afford to buy PCs for their own use and exercise rooms at the universities can be equipped with a large number of PCs (see Fig. 2).

At Aalborg University, 10 to 12 PCs are connected to a network. On the server with a large disc, the CAT/CAL programs are stored and downloaded to each of the PCs before the training session. The teacher's computer is connected to a projector which permits a colour display (RGB) on a large screen.

And last but not least, the students are very much motivated to use and master the computer. Fur- thermore, the Internet may influence education in photogrammetry. As the development of photogrammetric CAT/CAL software for the Internet is only beginning, only first experiences can be discussed here.

3. The PC and its components

The availability of low-cost PCs is one of the major reasons that CAT/CAL are already very much used. The PC becomes more and more powerful and is used already by children for games and other entertainment. A short discussion of the potential of personal computers for CAT/CAL follows:

3.1. Hardware

The technical progress in PCs and their peripheral units is very rapid. It is combined with a drop in prices. The high rate of change and the great variety in computers can, however, also be a problem. It is partially solved by new designs with compatibility to previous models or simulation of various operating systems in one machine (cross platform compatibility). This trend is realized, for example, in the Power PC processor of Apple/IBM/Motorola. The most recent IBM-compatible PCs with Intel proces- sors (Pentium, Pentium MXX) have a high processor speed (200 MHz) and a large expandable memory (4-264 Mb RAM). Special graphics adapters enable the display of highly resolved colour pictures on large-sized screens. For presentation in a classroom, one can use a portable computer in combination with a compact and bright multimedia projector.

Peripheral units include optical discs, tape cas- settes, compact disc drives of high storage capacity and high speed modems. Microphones and loud- speakers can also be part of the computers. 650 Mb of data and/or programs can be stored on CD- ROM and read into the computer. This new storage

J. HOhle /1SPRS Journal of Photogrammetry & Remote Sensing 52 (1997) 266-276 269

device supports the application of sound, speech, images and films - - the so-called multi media. Nowa- days, CD-ROMs can be produced relatively cheaply (H6hle, 1994).

3.2. Software

The innovations in software are enormous and cannot be dealt with here in detail or completely. For our task of teaching, photogrammetry, the important innovations include operating systems, professional image processing software and authoring tools. Dur- ing the last few years, new operating systems have been introduced, for example System 7 (MacOS), Windows, Windows 95, Windows NT, OS-2, and NextStep, etc. They support a graphical user interface, multiple windows and multimedia. System 7, the operating system of the Macintosh computer and its extension QuickTime, for example, handles films including sound and compresses images before storage. There are several professional image processing software packages which can be used in this type of education, for example, 'Photoshop' from the Adobe Corp., or 'Photostyler' from the Aldus Corp. All the programs mentioned can read images of various formats and transfer them to different formats, including compression. Furthermore, they can measure image coordinates, change the size, resolu- tion, contrast, brightness and apply filters. Examples of professional graphics programs are 'AutoCAD' from the AutoDesk Corp. and 'Microstation' from Bentley Systems. These two programs can be used for graphical design, mapping, and 3D presentations. Images can be imported and used as background information. For example, one can map on top of orthoimages and the result is a geometrically correct map.

When producing CAT/CAL programs, one can use several software tools. One can start from scratch and use standard programming languages, such as Pascal, C + + or Prolog. For all of these programming languages, toolboxes exist which include elements of the user interface, for example pull-down menus, input and message boxes, etc. For the development of CAT/CAL programs, an application generator is helpful. The user interface can be designed graphically and the source code of a selected programming language is generated

automatically. A further possibility is an authoring program. Advanced authoring programs for the Mac- intosh computers are 'Supercard 3.0' from Allegiant Technologies and 'Director 5.0' from Macromedia. The latter one is in the same price category as the personal computer itself. An interactive instruction by the 'Media in motion' Company will teach the proper use of this universal authoring program. More details about authoring tools can be found in SEFI (1991) and Hrhle and Stubkja~r (1991).

4. Other platforms for CAT/CAL

4.1. UNIX-based workstations

CAT/CAL can be carried out on UNIX-based workstations as well. Professional software for various applications has been specially developed on these machines. The CAT/CAL programs are then a supplement to the professional software and are usually called tutors. The advantage of UNIX-based workstations is that they have a better performance in general, e.g. large screens and special graphics adapters, which enable a fast and secure run of the programs and a nice display. Their use within a network (e.g. the Internet) is more efficient and more safe.

4.2. The Internet and the JAVA Virtual Machine

The Internet can be used as a computer system as well. It is basically a network of networks which connect thousands of computers around the world. There are clients and servers in the World Wide Web (WWW). By means of browsers one can fetch and display information sitting in remote servers. In order to make the displayed pages of information interactive, one can use the Java system in addition. The fundamental idea of the Java system is the spec- ification of a new computer architecture - - the Java Virtual Machine (JVM). The Java system consists of three parts:

(1) a Java compiler that converts the Java source code into bytecode instructions which are understood by the JVM;

(2) a browser that can transfer the bytecoded programs (the so-called applets) from the server to the client; and

270 J. HOhle / ISPRS Journal of Photogrammetry & Remote Sensing 52 (1997) 266-276

(3) a bytecode interpreter which simulates the JVM on the client machine and interpretively exe- cutes the bytecode.

This means that CAT/CAL programs written in the Java language will run on any client machine; they are therefore platform-independent. The only condition required is that a browser and an interpreter are installed, which can interpret the applets (this means that the byte code of the applets is translated line by line into a code which the computer of the client can understand). Fig. 3 shows the process during the development and the process when the user runs the CAL program at his computer.

Browsers which can read applets are for example Navigator (from Netscape) and Hot Java (from Sun Microsystems). Applets can run real-time 3D visualizations, animations, receive live data feeds, and support two-way interactions with other users. With these and some other features, CAT/CAL programs can be realized on the Intemet. The developed programs should also be stable, and high se- curity can be achieved. More information on Java can be found on the Web, e.g. at http://www. gamelan.com/noframe/Gamelan.programming.html. A Java compiler can also be downloaded as freeware which saves development costs. The Java language is object-oriented and is becoming more and more used. Other uses of the Internet for education in remote sensing are described in Stubkjaer (1997).

5. Some examples of CAT/CAL programs

In the following, some examples of CAT/CAL programs for education in photogrammetry are presented. They were developed at Aalborg University and used in the education of land surveyors. Programs from other educational institutions, as well as some tutors for professional products, will be mentioned.

applications of digital orthophotos are also themes in this learning program. The presentation of knowledge is accompanied by exercises. The exercises require computations using given formulae or exper- imenting with dynamic figures where the effect of various parameters can be studied. A calculator and an additional explanation can be displayed and used if required. The answer to the keyed-in solutions is immediately checked and statistics of the overall results can be printed out. The use of the program is extremely simple, only a few keys are necessary to operate it. The texts of the programs can easily be transferred to other languages. More details can be found in H6hle and Stubkj~er (1990). The program is freeware and can be downloaded from the Intemet (address: http://www.i4.auc.dk/j h).

5.2. ANALYT

The purpose of this leaming program is to train the student in analytical photogrammetry. In con- trust to the previous program, 'ANALYT' is an open program. This means that the source code can be inspected, changed and compiled. Running of the program can be stopped or intermediate results can be observed. The presence of the 'Integrated Devel- opment Environment' of the programming language (here PASCAL) is, therefore, necessary. In this way, the programming of the formulae can be inspected as well as the translation of the formulae into program codes. More details can be found in H/Shle (1992).

Both of the above-mentioned programs run on low-cost IBM compatible computers, which have an EGA or VGA graphics adapter. They are used in the education of land surveyors at Aalborg University and at some other places.

5.3. LDIP

5.1. ORTO

This learning program provides knowledge about aerial photography, rectification of aerial photographs and the production of orthophotos. An orthophoto can be integrated with topographic and thematic maps and a Land Information System or a Geographic Information System (GIS) can be built up. The basics of digital imagery and the different

The learning program 'LDIP' explains the theory behind automatic measurements step by step and provides exercises for each step. These exercises are either calculation tasks or experiments. The keyed-in solutions to the given tasks are analyzed by the program and an answer (wrong or correct) is given to the student. Detailed information about LDIP can be found in H6hle (1996a,b). Some of the features are presented below.

J. H6hle / ISPRS Journal of Photogrammetry & Remote Sensing 52 (1997) 266-276

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[ Internet I Fig. 3. Flow of a Java program from the developer's computer to the user's computer. The source code is compiled to bytecode and contained in the file (.class) and stored on a WWW server. From now on it is accessible throughout the Internet. The client's browser downloads the bytecode so that it can be run by the interpreter. Notice that it is the bytecode interpreter that is different from client to client (X ... MacOS or Windows 95, or Solaris (Unix)).

When a theme is selected, the information about this theme is presented. This occurs by means of one or two screen images with text and figures. Text is written on the screen, and additional information can be displayed into a window when it is wanted. The attached figures and images are dynamic. The information is presented as a sequence of text lines. They can be repeated if required. Several exercises are connected to the themes. The student is active and manipulates a figure or calculates values. The user interface is graphical and very simple. There are only a few fields with icons and texts to point to in order to activate a function or a process (see Fig. 4). The icons at the bottom line are used for navigation through the program, the ones on the right side for the manipulation within the displayed screen image. Pointing occurs by means of the mouse (or the track pad). A 'help' window informs the operator of the next steps to be carded out. A simulated pocket calculator can be used for the calculation of the results. The language in the blocks is English.

Some other features of LDIP are a pop-up menu with the available themes and hypertext which after activating opens new windows with new information (images, formulae, texts, etc.). The formulae use Greek letters and mathematical symbols. Fur- thermore, extensive calculations can be carried out with changing sets of data. The results are typed in the input areas and are immediately sensed by the program. LDIP features a high degree of interactivity which forces the students into an active role.

LDIP is designed as a stack of cards and can easily be extended with new cards. The software is also written in Think Pascal and runs under 'System 7.5'. This operating system also contains toolboxes with numerous functions for the development of CAT/CAL programs, such as pop-up menus, input and message boxes, icons, image and sound facili- ties. Images, icons and sound are stored in resource files and can easily be exchanged or new ones can be added. The programming of LDIP is partially object-oriented, which means that objects such as

272 J. HOhle I ISPRS Journal of Photogrammetry & Remote Sensing 52 (1997) 266-276

THEME 1" AUTOMATIC MEASUREMENT

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windows are set up with their attributes (size, position, etc). The program runs on Macintosh computers only.

The use of the program is manifold. It can be used in the classroom as part of the lecture, or in the exercise room with a number of computers/students or by the student in self-study on his or her own computer at home. At presentations in the classroom, a multimedia-projector such as the EPSON 3300 is of advantage. This compact projector enables a bright picture with good colours to be presented on a large screen. The use of LDIP in the exercise room (e.g. equipped with 12 Macintosh computers) allows an efficient education and communication between students and between student and teacher. The program is freeware and can be downloaded from the Intemet (address: http://www.i4.auc.dk/jh).

5,4. LDIPInter

In order to use the Internet as a tool in CAT/CAL, a new development has been started by the author in autumn 1996. This program, LDIPInter, is written in the Java language and compiled by the Java compiler into bytecode and stored on a server at Aalborg University. By means of a browser the bytecoded program (applet) is transferred from this server via the Internet to a remote client machine on which an interpreter will simulate the Java Virtual Machine and execute the bytecoded program. LD1Pinter cov- ers the theme 1 and task 1.1 ("Find manually the position of the best fit and calculate correlation coef- ficients at this position") of LDIP for the time being. It was designed to allow experience with CAL/CAT programs on the Internet and to be used as an introduction to LDIP.

J. HOhle /ISPRS Journal of Photogrammetry & Remote Sensing 52 (1997) 266-276 273

Fig. 5. Screen image of task 1.1 in LDIPInter.

Fig. 5 shows the elements which have to be imple- mented: text, graphics, calculator, windows, buttons, input fields, animation. The following remarks can be made at this point of time:

Text. Latin and Greek letters can all be realized thanks to the 16-bit unicode available in the browser used (Netscape Navigator). This means that 65,536 characters are at our disposal. This opens the possibility of using text with non-Latin letters (Greek, Arabic, Cyrillic, Hebrew, etc.).

Graphics. Lines cannot vary in thickness in Java version 1.0, but can be of different colour.

Windows. They are easy to generate thanks to the inheritance ability of objects in the graphical library (java.awt). The objects within the windows (icons, input fields and buttons) are placed by a so-called layout manager. A problem arises if text or graphics have to be placed in between. This is done by means of coordinates in contrast to the floating positioning by the layout manager.

274 J. HOhle / ISPRS Journal of Photogrammetry & Remote Sensing 52 (1997) 266-276

Buttons. These can be created. After pointing and clicking, one can activate e.g. a display of a window.

Calculator. There are many freeware 'calculators' on the Web to which the program can link. It is better, however, to integrate a calculator (applet) into the CAT/CAL program.

Icons. These are difficult to realize (compared with the Macintosh toolbox). But examples can be found on the Web.

In general, programming in Java is relatively simple; Java has many similarities to the C + + language. The transfer of LDIP, which is written in Pascal, to LDIPInter therefore used a 'Pascal to C' translator. Procedures within procedures, however, cannot be used which increases the number of variables in the program.

Compiling Java source codes is slow, which only affects the development work. The development requires a lot of memory and speed. Therefore, powerful machines are recommended. Programming in Java and executing Java programs is more secure due to the many built-in safety precautions and warnings.

6. Experiences of use

6.1. ORTO

The program has been used for several years at Aalborg University and some other universities with good results. Recent experience with its use in distance learning is also positive. The fast im- provements in computers and the lack of continuous updating has made the program somewhat old-fash- ioned.

6.2. ANALYT

The program was used in combination with picture taking and evaluation of terrestrial photographs. One's own data can be used, which is, of course, motivating. Some students were stimulated to carry out their own program development in later project work.

6.3. LDIP

Students preferred their own pocket calculator and enjoyed the feeling of success when correct

answers were typed in. The stability of the program was not optimal on some computers. The topics with adjustment calculations gave some difficulties, but English as a foreign language did not cause problems in the understanding.

6.4. LDIPInter

The translated parts of the LDIP program are installed on a server of Aalborg University and can be accessed from there using the following address: http://www.cs.auc.dk/-~hoehle/LDIPInter.html.

Fig. 5 shows the screen image of task 1.1 which is created by the Java program. It runs as an applet in HotJava (version 1.0).

The contents should be the same as in Fig. 4. To run the program the student has to use the Hot Java browser and download the applet using the address given above.

This can be done on different client machines, in our case: Macintosh Power Book 520, Silicon Graphics, Sun Ultra and Pentium (with the operating system Windows 95 or Windows NT). The HotJava browser does not run on DOS machines and the LDIPInter cannot be used on PCs with this (old) operating system. Therefore, the platform indepen- dence of JAVA programs is not fully true. As the reader may try himself, LDIPInter is downloaded from the Web in a few seconds. The loading time de- pends on the performance of the computer used and the 'traffic' on the Web. But under good conditions, it takes just a few seconds. The loading time can be considerably reduced by downloading the bytecode file onto the disk of the client and starting it from there. The execution of the program is relatively slow if compared with the Pascal program. This is due to the interpretive language which processes line by line. The important fact is, however, that LDIPIn- ter runs on all the mentioned computers without any installation headaches.

7. Other photogrammetric CAT/CAL software

Several other universities have developed CAT/CAL software as well. During the last IS- PRS congress in Vienna, the first software contest for Computer Assisted Teaching (CATCON) took place and several other programs from the field of

J. HOhle /ISPRS Journal of Photogrammetry & Remote Sensing 52 (1997) 266-276 275

photogrammetry were presented (Georgopoulos and Fotinopoulos, 1996; Nelson, 1996; Li Deren and Tao, 1996).

There were several more CAT/CAL programs that covered related fields such as Image Analysis, Remote Sensing and GIS and which used pedagogical principles. CAT/CAL programs have to be dis- tinguished from production programs which solve a special task. Also the industry has developed CAT/CAL software which can be classified as a tutor to professional software packages, systems or data sets.

Examples are a CD-based introduction to the digital stereoworkstation 'DiAP' from the ISM Corpo- ration and Rollei's tutor for their new 'Close Range Digital Workstation' (CDW). The main purpose of these tutors is to reduce cost and effort for training of their clients and to give support in trouble shooting. Special multimedia tutors will replace or support the manuals to sophisticated commercial products.

8. Conclusion

CAT/CAL in digital photogrammetry requires a large amount of data and complex calculations. The new PCs with their high processing speed and large internal and external storage capacity (such as CD- ROMs) make a new type of learning program possi- ble. These CAT/CAL programs can include speech, image libraries and heavy calculations. The user interface is simpler and more attractive due to icons, sound and various windows. The efforts for development are relatively high and require detailed knowledge of toolboxes as well as good programming experience. Also very advanced author programs are available which will ease the production of good CAT/CAL programs for authors with less experience in programming. There will, however, be restrictions with regard to the computers which can be used. There are programs especially made for a PC or a Macintosh or professional workstations. Different operating systems and hardware configurations (e.g. graphics card, CD drive, etc.) will also prevent the universal use of the developed CAT/CAL programs. The JAVA Virtual Machine (JVM) is possibly the solution to this problem. CAT/CAL programs imple- mented in the Java language run on machines which have a Java-based browser. The programming in Java

is easier than in Pascal or C + + because an Applica- tion Programming Interface can be used (freeware). The cooperation of programmers around the world seems to be feasible in order to produce computer- assisted learning programs. Links to existing programs can be established. Especially attractive is the use of many platforms without installation problems. The disadvantage of Java programs on the WWW is the explosively growing number of participants which may delay the execution of the interactive CAL programs in the future. The DOS systems are excluded from use of Java-based programs on the Internet. All in all it is worthwhile to proceed with Java as a tool to develop and to use CAT/CAL. Whatever the technical solution will be in future, CAT/CAL will gain in popularity in education in photogrammetry and other fields.

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Georgopoulos, A., Fotinopoulos, V., 1996. 'Photogrammetrist v. 1.0': the Greek introduction to photogramrnetry. Int. Arch. Photogramm. Remote Sensing, Commission VI, pp. 45-50.

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Hrhle, J., Stubkjaer, E., 1991. A comparison of the development

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tools for the LISdemo project with selected authoring tools. In: Proceedings of the International Conference on Computer Aided Learning and Instruction in Science and Engineering (Calisce '91), Lausanne, pp. 561-565.

Li Deren, Tan, 1996. WuCAPS, Package for GPS supported aerotriangulation and quality analysis of adjusted results. CAT- CON entry, XVIII ISPRS congress, Vienna.

Nelson, J., 1996. PC-TAS: PC-tooled analytical stereo-modelling making use of Microsoft Exel for education in basic analytical photogrammetry. Int. Arch. Photogramm. Remote Sensing,

Commission VI, pp. 11-113. SEFI, 1991. Proceedings of the Conference on Authoring Tools,

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Computer-assisted teaching and learning in photogrammetry