An interactive Web-based teaching tool for simplified 3D analysis of solar rhythms

Ž .Automation in Construction 8 1998 181–194

An interactive Web-based teaching tool for simplified 3D analysisof solar rhythms

Archit Jain, Karen Kensek, Douglas Noble )

CLIPPER LAB, School of Architecture, UniÕersity of Southern California, 204 Watt Hall, Los Angeles, CA 90089, USA

Accepted 5 May 1998

Abstract

This case study presents the World Wide Web as an appropriate medium for architectural teaching. The prototypical toolVRSolar uses simple programming and existing Web resources to help in the teaching of topics related to the movement ofthe sun and its effects on the built environment. Using JavaScript, this tool is capable of generating real time Web content inhtml and VRML based on user input. Accessible on the Web from within a standard Web browser, this tool calculates thesolar positions of any location on earth and indicates the solar access to a given site in the form of a three-dimensional Webpage, which the user can view, navigate through, and animate. q 1998 Elsevier Science B.V. All rights reserved.

Keywords: Web-based teaching; VRML; JavaScript; Html; Solar rhythms

1. Introduction

The Web is becoming increasingly used as aninformation bank and a method of transmittingknowledge to students. It is a widely accessibleresource for students, instructors, and professionals,and recent advances in Web technologies make ithighly suitable for the development of interactivetools that can take advantage of the multi-platformand location independent range of resources that theWeb can access.

The Web-based teaching tool ‘VRSolar’ was de-veloped as a prototype program to teach solar con-cepts to students and to serve as a convenient practi-cal tool for information on solar positions and move-ment. Solar rhythms was chosen as the basis for this

) Corresponding author

study for many reasons: the understanding of thesun’s movement is essential for designing climati-cally responsive and energy saving buildings; theinformation is usually available in the form of solartables and sun charts that are often not convenient toaccess or comprehend especially by the students; andthe Web provides an easily accessible, powerfulmethod for teaching.

VRSolar was created to calculate the position ofthe sun at a particular day and time and to help usersunderstand the sun’s movement over time. It in-cludes a ‘Solar Calculator’ to generate the positionof the sun for a particular place, date, and time,plotting the sun positions in the form of Mazria’s

w x Žcylindrical sun chart 1 . It uses VRML Virtual.Reality Modeling Language as a basis for making

primitive interactive three-dimensional computermodels as shown in Fig. 1. The user can navigate

0926-5805r98r$ - see front matter q 1998 Elsevier Science B.V. All rights reserved.Ž .PII: S0926-5805 98 00072-7

( )A. Jain et al.rAutomation in Construction 8 1998 181–194182

Fig. 1. Overall view of the VRSolar interface showing an exampleVRML computer model.

through this model and observe the shadow implica-tions of the built form on the open space.

2. Using the Web for instruction

Online versions of course contents, with searchcapabilities, indexing, online discussion forums, andon-the-fly-generation of Web content are becomingincreasingly common. For example, at the Universityof Southern California, online courses on OralPathology and Communications and Art were earlyexamples that demonstrated the possibilities of

w xWeb-based teaching 2 . The Oral Pathology pagesfeature interactive searching for terms, an automatedself-exam to study for State Board Examinations,and an online dictionary. In the Communicationspages, comparative study and extensive cross-refer-encing make self-study easier.

The Web is also being used for instructionalsupport material on courses related to architecture. Anotable example is the use of ‘enhanced, annotatedand manipulated’ digital images on the Web to teach

w xstructural concepts 3 . Others have used the Web asa community resource, where the students and the

w xteachers can discuss projects and get feedback 4 .From the University of Colorado, the PHIDIAS IIsystem aims at using VRML and Java on the Web asthe front end for collaboration by distributed designteams, working together on a PHIDIAS hyperCAD

w xsystem 5 . The Architectonics Studio at the Univer-

sity of Oregon uses Java in creating tools for teach-ing structural concepts. These teaching tool featuresJava Applets that can be run over the Web for

w xteaching structural concepts 6 .Some Web-based tools teach by showing exam-

ples. Yet the Web is capable of much more, evenwhen using simple programming methods, as manyof these previous examples have shown. VRSolar isa calculation tool that allows the user to input infor-mation about the appropriate site considerations andthen simulates the behavior of the system. In addi-tion, there is a glossary of terms to help the studentsuse the program and understand the results.

3. VRSolar as a Web-based tool

Because VRSolar is a Web-based tool, it has nospecific computer hardware requirements althoughfaster machines do provide for better interaction. Allthat is required is a Web browser capable of inter-preting standard html and JavaScript, such asNetscape 3.0 or Internet Explorer 4.0, and a VRML

Ž .2.0 browser usually as a plug-in to an html browser ,w xsuch as Cosmo Player from Silicon Graphics 7–10 .

3.1. DeÕelopment of VRSolar

VRSolar was developed to run on the Web. Itsdevelopment involved no high-end CGI-bin pro-gramming, nor did it involve the use of any expen-sive authoring programs. Tools like VRSolar can bedeveloped by anyone who has access to post Webpages. JavaScript for VRSolar was first keyed into atext editor along with the html code. When thesepages are opened by the Web browser, the Webbrowser itself works as the debugger, and the correc-tions to JavaScript can be made. No other program-ming packages were needed.

Once the pages for VRSolar were tried and testedon the computer where they were being writtenŽ .network access was not required , the pages wereuploaded to the Web pages from where they canbecome universally accessible. The only special carethat needed to be taken for VRSolar was to add theMIME type for the VRML.wrl files on the server asx-worldrx-VRML. This ensures that the browsersrecognize the VRML file being opened and bring upthe proper VRML plug-in.

( )A. Jain et al.rAutomation in Construction 8 1998 181–194 183

3.2. HTML

In an html page, the JavaScript is embedded ascode. The coding is fairly straightforward, as shownby the example below. When the user selects LosAngeles, the program checks if the selected value is34.0, and displays an alert.

-SCRIPT LANGUAGEs‘JavaScript’)

- !– Start hiding script from old browsersrrFUNCTION CHECK_FOR_LA

Ž . �function check_for_la valueŽ . �if valuess34.0

Ž .alert ‘Thank you for choosing Los Angeles!’4 �else

Ž .alert ‘That surely is not Los Angeles!’4

4rrend hiding script –)

-rSCRIPT)

3.3. VRML

With VRML, it is possible to define the geometryof a place and allow users to navigate in a three-di-mensional space in addition to retaining hyperlinks.VRML and its development is relatively new. Thefirst draft of VRML was specified in July of 1995and VRML 2.0 or Moving Worlds was specified asearly as August 1996. VRML, like other Web-basedtechnologies, is still in transition, though it hasachieved many new capabilities in the 2.0 versionw x11 .

In practice, VRML is a text-based language, whereobjects are defined as geometries in this modelinglanguage. As an example, the following code de-scribes a red box of dimension 7=5=2 m inVRML 2.0.

aVRML V2.0 utf8�Transform

center 0 y0.5 0translation 0 0.5 0

�children Shape�appearance Appearance

�material MaterialambientIntensity 0.1diffuseColor 1 0 04

4�geometry Box

size 7 5 24

44Once the page is viewed through a Web browser,

the user can navigate fairly easily through the geom-etry produced. The viewer also has the opportunityto view the model from predefined view points, thatmay have been specified in the VRML geometry andhear sounds coming on nodes within the VRMLworld.

3.4. JaÕaScript

The program uses the Web browser as a base forprogramming in JavaScript. JavaScript, developed byNetscape, is a script-based language, simple and

w xflexible 12 . JavaScript is interpreted at runtime andexecuted by the Web browser itself. As a scriptinglanguage, it offers programming tools to a muchwider audience because of its ease of syntax, special-ized built-in functionality, and minimal requirementsfor object creation. In VRSolar, JavaScript is used asthe method of generating new html and VRMLbased on user interaction. The html pages are dis-played by the browser itself and the VRML plug-inis responsible for interpreting and displaying thethree-dimensional data. In addition, embeddedJavaScript in the opening page checks for the versionof the Web and VRML browser that the user iscurrently using and used for the calculations that aredone.

A benefit of using JavaScript is that Web accessis not constantly needed. JavaScript is a client-sidelanguage. Therefore, JavaScript is interpreted by theWeb browser and not by the server, where the pagesreside. Once the page is read by the local computer,there is no more communication taking place withthe Web server. All further calculations occur di-rectly on the local machine.

Working with a language such as JavaScript doeshave its limitations. JavaScript works on a modelreferred to as the ‘sandbox effect’ and is unable tomake any system calls. The browser cannot do any-thing outside the browser window. This is an inten-tional characteristic, driven by security considera-tions, that helps to avoid writing Web pages directlyonto the user’s hard drive. For VRSolar, this meansthat the program by itself would not be able to save


Fig. 2. The secret section of the menu bar, not visible to users, passes values between frames.

files on the users local drive. The computation withinŽ .the program occurs in RAM and in the cache of the

computer. The resultant pages are held in the mem-ory buffer and in the cache of the browser and arenot permanently recorded.

This limitation requires a workaround for savingthe files onto the users local drive. Another compli-cation is that JavaScript cannot pass variables fromone page to the next. This means that all the valuesthat the users provided and generated while using

Ž .one part of the program the Solar Calculator cannotŽ .be passed to another page the VR Builder . There-

fore, another workaround was required; the sidemenu bar actually acts as a buffer storage to hold the

Ž .values. This part of the menu bar Fig. 2 is notaccessible to the user due to the frame restrictionsapplied in the html.

4. Capabilities of VRSolar

The primary capabilities of VRSolar include gen-erating the position of the sun for a particular place,

date, and time as shown, plotting the sun positions inw xthe form of Mazria’s cylindrical sun chart 1 , and

inputting the site and the surrounding buildings via abuilt-in elementary geometry defining program writ-ten in JavaScript. VRSolar generates the informationas a VRML world file for view from anydirectionrangle and walk through the site. In thisway, it allows for the animation of solar position andpath, and permits users to input their own modelsinto the solar VRML thus generated, so that the sitecan be viewed with the users’ built form. The solarmodel can be imported to other modeling softwareby using Autodesk’s DXF file format. More featuresare anticipated as shown in Fig. 3.

VRSolar is comprised of three main sections, theOpening Screen, the Solar Calculator, and the VRBuilder. The Solar Calculator calculates the positionof the sun as defined by location, date, and timevalues provided by the user. The VR Builder com-bines the resultant solar location with the geometrythat the user supplies and dynamically generates aVRML scene that has both the building geometry


Fig. 3. Program development organizational chart.


Fig. 4. The opening screen.

and the solar geometry. In addition to the three mainsections, the other components are the sunrisersunsettimes, help files with conversions and definitions,Web indices and resources, and resources for thistool.

4.1. Opening screen

Ž .The opening screen Fig. 4 is written in simplehtml so that even the most basic browser can open it.Upon opening, VRSolar checks for the version of theWeb and VRML browser that the user is currentlyusing. It then informs the user about the require-ments for the program and the software needed torun it. The user can also download the needed soft-

ware off the Web through the links that point to htmland VRML browsers and other utilities.

The opening page also provides two other impor-tant links for first-time users: ‘Before you Start’ and‘How to Use’. The first link takes users to a pagethat describe the program and the software needed torun it. The pages also provide information on thecapabilities of VRSolar and links to example VRMLfiles generated by using VRSolar. The second linkgives step by step instructions to the user for theprogram. After the users have acquired any neededsoftware, they can proceed to the program itself.

Ž .The program’s primary interface Fig. 5 consistsof the menu bar to the left, the help files on thebottom, and the main screen on the right. The main

Ž .menu on the left lists the choices for proceeding: 1Ž .Solar Altitude and Azimuth Calculator, 2 Virtual

Ž . Ž .Reality Builder, 3 SunsetrSunrise Times, H HelpŽ .Files, Conversions, Definitions, V Web Indices and

Ž .Resources, and R Resources for this Tool.

4.2. Solar Calculator

Ž .The Solar Calculator Fig. 6 is used to calculatethe position of the sun at a given time and location.The location of the site can be chosen by city namefrom the drop down menus, or if a particular city isnot listed, the latitude can be entered numerically. Itis also possible to choose a rough approximation ofthe location by clicking on the graphical world map.

Fig. 5. The main menu.


Fig. 6. Location and time input interface.

The user chooses the date and time desired for thecalculation from the drop down menus provided.From the date, time and location provided, VRSolaruses JavaScript to calculate the following solar val-ues: Julian day, declination, hour angle, altitude and

Ž .azimuth Fig. 7 . It displays latter two results in theform of the table shown in Fig. 8 that can be printedfrom within the browser.

The Solar Calculator uses standard formulae tow xcalculate the solar altitude and azimuth 13 . When

the Solar Calculator has calculated the values for theazimuth and altitude, the program dynamically writesthe new html page to the other frame in the windowthat shows the calculated result. The MIME type forthis new page is set as textrhtml, and therefore, thepage is displayed as formatted html within thebrowser. The html for this generated page is within

Fig. 7. Altitude and azimuth calculator showing Buenos Aires asan example.

Fig. 8. Generated sun plot for a given time.

the JavaScript of the program that concatenates thetext strings and writes the new page.

4.3. The VR Builder

Once the location of the site has been described,and the solar positions calculated, the VR Builderguides the users to input the geometry of their ownsite and buildings into the program and view how thesun moves with respect to the structures. The chiefaim of VRSolar is to help users decide what areas oftheir site are in shade and which are in sun. VRSolarhas the capability of letting the users input their sitesplus any adjacent buildings and trees.

4.3.1. Using VR BuilderThe users can select the units in which they want

to work. The distance units can be chosen from feet,meters, inches or millimeters. For angles, the unitscan be degrees or radians. By convention, the unitsfor distance for VRML files is meters, therefore, inthe VRSolar generated VRML files, all the units arein meters. Also by convention, all the angles are inradians.

VRSolar accepts both rectangular and irregularsites. For simple rectangular sites, the length and thewidth of the site can be entered. The orientation ofthe site can be specified as angular units if the site isnot along the cardinal directions. For non-rectangularsites, the VRSolar allows users to have up to aseven-sided site, which may be entered as coordi-nates.


For the prototype version, VRSolar allows foronly three different generic tree shapes. Users candecide the number of trees, the location, and theheight and width of each tree. Transparency of thetrees is intended as a feature in the next version ofthe program.

Buildings adjacent to the site can be input VRSo-lar with the x and y coordinates of the center pointand the length, width and height dimensions. Cur-rently, VRSolar only allows rectangular shapes, butthese can be combined to create more complex ge-ometries. Different colors chosen for these buildingscan identify them in the generated VRML scene.

By default, VRSolar generates five viewpoints.One from each cardinal axis and another from thetop. The user is given an option to enter a sixthviewpoint from a custom point. These viewpoints areavailable to the user through the VRML browserinterface. Users have the option of changing thedefault viewpoints and creating custom views, whichwould be more specific to that particular site. Be-cause of the nature of VRML files, the user is free tonavigate interactively through the three-dimensionalcomputer model.

4.3.2. Understanding how VR Builder worksThe VR Builder, using the same algorithm as the

Solar Calculator, assembles the VRML file based onthe user input. VRML files are also text files.JavaScript can therefore simply write out the gener-ated text to another newly created browser windowon-the-fly. Since VRSolar sets the MIME-type forthis new window as x-worldrx-VRML, the VRMLbrowser for seeing the generated VRML comes upautomatically.

Prototypes for the usable primitive shapes aredefined in the program. If the user specifies a build-ing or tree using a particular prototype, the programincludes the prototype for that shape in the generatedVRML file and then instances the prototype with thecorrect parameters. The generated shape now be-comes the user’s building or tree.

Consider a simple example of two user-specifiedrectangular buildings. JavaScript automatically in-serts the rectangular building prototype in the gener-ated VRML file.

wPROTO rectBuildingfield SFVec3f buildingTranslation 0 0 0

field SFRotation buildingRotation 0 0 0 0field SFVec3f buildingScale 1 1 1field SFColor buildingColor 1 0 0x �

�DEF rectangularBuilding Transformtranslation IS buildingTranslationrotation IS buildingRotationscale IS buildingScale

�children Transformcenter 0 y0.5 0translation 0 0.5 0

�children Shape�appearance Appearance

�material MaterialambientIntensity 0.1diffuseColor IS buildingColorshininess 0.24

4�geometry Box

size 1 1 14

444

4The geometry of the rectangular building, which

is essentially a box on the ground plane of theVRML scene, is now defined as a prototype objectcalled rectBuilding in the VRML file. In the proto-type, the first four lines are the fields for the transla-tion, rotation, scale and color of the buildings, whichare the user defined variables.

Once the prototype has been defined, two build-ings can be described as:

�rectBuildingbuildingTranslation y7.62 0 y27.432buildingScale 39.624 18.288 15.24buildingRotation 0 1 0 0buildingColor 1 0 0

4�rectBuilding

buildingTranslation 6.096 0 21.336buildingScale 30.48 6.096 18.288buildingRotation 0 1 0 0buildingColor 0.66 0.489909 0.12528

4This method is far more efficient for producing


VRML files with previously specified geometry.Since the location of each vertices and their respec-tive properties coupled with the fact that the entirebuilding is one entity and not made up of manydifferent three-sided faces, the size of VRML filescreated by this program is vastly smaller than thosegenerated by many VRML generating programs.

Viewpoints are generated by utilizing the posi-tions of the sun calculated in the Solar Calculator.Rotations about the x and z axes are required toview the site correctly from the position of the sun.VRML describes rotations in the format ‘x y z rot’,where x, y and z are numbers between 0 and 1,which define the percentage of each axis along whichrotation is occurring, and rot is the rotation value inradians. This format of rotation could be calculatedby a program written in C, but integrating it intoVRSolar would not only mean converting the pro-gram into JavaScript, but also increasing the file size

w xtremendously 14 . This problem is resolved by ap-plying two rotations, one after the other, to theviewpoint positions, creating a not so elegant buteffective resolution.

VRSolar uses JavaScript to write out animationswithin the VRML 2.0 specifications. These anima-tions use the position of the sun calculated earlierand relate it based on mouse clicks. JavaScript canalso be embedded into the VRML for animationsnow, but this is only supported in the newest versionof the Cosmo Player.

The VRML files generated from within the pro-gram can be saved onto the user’s computer bygenerating the VRML as a text file, cutting andpasting it in a text editor, and saving it with ‘.wrl’ as

Ž .the suffix Fig. 9 . For security reasons, JavaScript

Fig. 9. Dynamically generated VRML file and source code.

does not write directly to the local disk automati-cally.

4.4. Help files

The help files include glossaries, conversion ta-bles, and links to files that users may need. Theglossary provides definitions to commonly used termsin computing along with the help for the programitself. The conversion tables include metric to stan-dard translations for distance, angle, and thermalcalculations. In addition, context sensitive help isavailable at all instances by running the mouse overthe headings. It is also possible to turn off the helpfeature to both reduce distractions and improve theperformance of slower computers, but this is notrecommended for novice users.

4.5. Web indices and resources

These pages are provided as admittedly incom-Žplete due to the ever changing characteristics of the.Web list of resources on the Web that may be useful

for the users of VRSolar. These links are categorizedunder the following headings: associations and orga-nizations; product information and specifications; en-ergy, sustainability, and automation; schools and de-partments; directories and other resource guides; anddiscussion groups.

[ ]5. Advantages and disadvantages of VRSolar 15

5.1. AdÕantages

VRSolar is substantially complete. Many of itsadvantages are inherent in the nature of a Web-basedteaching tool. For example, it can be updated andmade accessible easily and immediately. Once thefiles have been changed on the server, all the pro-grams change automatically. Students can proceed attheir own pace, and work from anywhere, at home orin school. Extensive hard-copy printing is not re-quired. The pages can be linked to external sourcesof information. Teaching material could have manylevels of detail, each at a separate level, that could beaccessed by students in any sequence. With the aid


of a projection device, the pages can be used tosupport lectures or hands-on lab sessions. The pagescan be used by prospective students to assess courseor to prepare for it and provides a broad audience forstudent work Since the pages are accessible aroundthe world, collaborative work is also possible. Re-cently, work has been started on the development ofa French version of VRSolar mirrored from a server

w xin France 16 .VRSolar, even in its present basic form, has

value. As a teaching tool, the program can helpstudents to understand the notion of solar movementeasily, remember concepts, and get online study forarchitectural science courses. It provides access forstudents to use in their calculations, without theeffort of searching for books and solar charts. Solarcharts which can be printed can help students workon their simulation models aided by this tool. Forstudio projects, it could be used as a quick andsimple method of determining solar access to sites

Ž .for initial design Fig. 10 . The geometric model datafrom VRSolar can then be transported into othersoftware.

In an architect’s office, VRSolar could be used asa tool to calculate solar altitude and azimuth and to

Fig. 10. Example images of a simple model as viewed fromvarious Solar positions.

create sun charts. It could also be run over anintranet, where the tool would work faster.

5.2. DisadÕantages

There are also disadvantages of the VRSolar sys-tem. Because the material on the Web is public, itcan easily by copied and used by others with nocredit given to the original author. Password protec-tion and limitation of use to certain servers can limitthis problem, but not prevent it completely. Thepages are open to inspection, comparison, assess-

Žment, and criticism from anyone colleagues, admin-.istrators, etc. , this being both a disadvantage and an

advantage. Students may get lost in a maze of exter-nal references. Preparation of the course material andprograms can be very time-consuming. Web-basedteaching presumes basic computer literacy on stu-dent’s part. Currently, a limitation of tools like VR-Solar is that the programs and languages that thetools are based on are still under development. Sincethe standards are continuing to evolve, the tools maynot perform equally well on all platforms and underall browsers. This results in a requirement to fre-quently update the program.

5.3. VRSolar in use

Though VRSolar has not been extensively used ina classroom, students and architects have experi-mented with it at many times. For users familiar withthe browser interface, using a large portion of VRSo-lar is easy. Generating valuable information usingthe Solar Calculator, printing the generated informa-tion, and applying it to their thermal or lightingcalculations was simple for most users.

Major problems arise when users want to inputtheir own buildings into VRSolar. Since the interfacerequires numeric information instead of a graphicbuilding input, many students found it difficult todescribe locations of buildings. In VRSolar, thebuildings’ locations are specified relative to the cen-ter of the site in terms of dimensions and angles.Architecture students especially who have had usedmodern three dimensional computer modeling pro-grams find this type of numeric input cumbersome.

This issue needs to be worked on with a Java-based interface where changes in input are instanta-


neously visible in the VRML scene. The other optionwould be to allow the users to attach their ownbuilding files to the solar geometry. The secondoption was not possible until recently, when thenewer versions of browsers have become availablethat allow development along these lines.

In addition, only very simple massing models canbe input, often frustrating the users as they try toapply this program to very specific studio projects orarchitects to real world conditions.

6. Conclusion

VRSolar demonstrates that the World Wide Webcan be used for the development of architecturalteaching tools that are interactive and platform inde-pendent. Improvements in both hardware and soft-ware are allowing faster access, which encouragesuse of the Web. JavaScript and VRML can and havebeen used to develop visually-based tools. JavaScriptis not difficult to learn and can be used for writingsmall architectural tools in the future. VRML hasgreat potential to be used not only for convertingthree-dimensional models to Web viewable walk-throughs, but for real-time dynamic generation ofthree-dimensional spaces. While the capabilities ofthe VRSolar program are currently limited, themethod appears promising.

Acknowledgements

We wish to thank Marc Schiler for his ideas andguidance, and Robert Doiel for inspiring the experi-ment. We also want to acknowledge the support ofthe USC School of Architecture 3DClipper Lab.

References

w x1 E. Mazria, Solar Concepts. The Cylindrical Sun Chart is avertical projection of the sun’s path as seen from the earth,The Passive Solar Energy Book, Chap. 4, Rodale Press,Emmaus, PA, 1979, pp. 302–322.

w x2 The Oral Pathology web page can be found athttp:rrwww.usc.edurhscrdentalropath and the Communi-cations and Art page is at http:rrwww.usc.edurdeptran-nenbergransc100r.

w x3 K. Martini, Digital Imaging and the Web in Teaching Struc-tures: A Rigorous Visual Approach, ACADIA 1996 Proceed-ings: Design Computation, Collaboration, Reasoning andPedagogy, ACADIA, Tucson, 215 – 225, http:rrurban.arch.virginia.EDUr ;km6erttirtti-summaryr.

w x4 An example is the Computational Composition by RobWoodbury at the University of Adelaide. http:rrwww.arch.adelaide.edu.aurdfr.

w x5 R.W. Knapp, R. McCall, PHIDIAS II—In support of Collab-orative Design, ACADIA 1996 Proceedings: Design Compu-tation, Collaboration, Reasoning and Pedagogy, ACADIA,Tucson, 147–154, http:rrphidias.colorado.edurphidias.

w x6 Developed at the University of Oregon by Prof. Chris H.Luebkeman with Eric Ngai and Elton Ng http:rrdarkwing.uoregon.edur ;structr.

w x7 HTML, the HyperText Markup Language, is the linguafranca of the Web.

w x8 http:rrwww.netscape.com. JavaScript, because of differ-ences in interpretation, did not work very well with theearlier versions of Microsoft Internet Explorer. However, it isfully supported version 4.0.

w x9 For a list of VRML browsers available for various plat-forms refer to http:rrwww.sdsc.edurvrmlrcgi-binrdisplay.cgi?categorysBrowsersqandqPlug-ins&.

w x10 http:rrcosmo.sgi.comr.w x11 For a general discussion on VRML, refer to VRML Fre-

Ž .quently Asked Questions Jan Hardenbergh at http:rrvag.vrml.orgrVRML_FAQ.html.

w x12 http:rrdeveloper.netscape.comrlibraryrdocumentationrco-mmunicatorrjsguide4rindex.htm JavaScript, now can alsobe used as a server side application, however, to maintainserver independence, this tool uses only the client side aspectof the language.

w x13 K. Kensek, Work In Progress: Solar Envelopes and SolarŽ .Zoning, ACADIA Quarterly, 14 2 , 1995. The lisp program

called CalcSolar, designed to generate solar envelopes inAutoCAD, provided the final versions of the formulae. Theformulae were taken from books on Solar Design, mainly

ŽCBRI, Climatological and Solar Data for India Meerut,.India: Sarita Prakashan, 1969 , and S.V. Szokolay, Thermal

Design of Buildings, Red Hill, ACT, Australia: RAIA Educa-tion Division, 1987.

w x14 orient.c written by Stephen Chenney prompts for a fromvector, an at vector, and an up vector, then calculates theorientation required to align the default VRML camera withthe given camera. The code is available fromftp:rrftp.cs.su.oz.aurstephenrvrmlrorient.c.

w x15 Though the advantages of the Web are generally known, thissection has been derived mainly from http:rrwww.wayne.edurwttrwtt.html and from http:rrseaccd.sccd.ctc.edur ; jkentrntcforumrindex.htm. For a generaldiscussion on Web-based teaching and related topics, refer tohttp:rrwww.csv.warwick.ac.ukraltEralt-C95rpapers.html.

w x16 http:rrwww.kubos.orgrutilsrframeset.html.

An interactive Web-based teaching tool for simplified 3D analysis of solar rhythms

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