THE INFORMATIVE VISUALIZATION METHOD OF THE 4D CAD … · 2013-11-25 · 114 Informative Visualization Method of 4D CAD Model adding up as planned sequences from the project commencement

Suranaree J. Sci. Technol. 16(2):113-125

1 School of Civil Engineering, Institute of Engineering, Suranaree University of Technology, NakhonRatchasima, Thailand. E-mail: [email protected]; Fax.: 66 (0) 44 224607; Tel.: 66 (0) 44 224172

2 Department of Civil Engineering, Faculty of Engineering, Ubon Ratchathani University, Ubon Ratchathani,Thailand. E-mail: [email protected]; Fax.: 66 (0) 45 353333; Tel.: 66 (0) 45 353306

* Corresponding author

THE INFORMATIVE VISUALIZATION METHOD OF THE4D CAD MODEL

Vacharapoom Benjaoran1* and Sdhabhon Bhokha2

Received: Jan 29, 2009; Revised: Apr 3, 2009; Accepted: Apr 22, 2009

Abstract

A novel construction schedule presentation called the 4D CAD model is able to explicitly demonstratethe construction sequence and working space in 3D visual. However, it still has some shortages and isused as a supplementary presentation. This research identifies the deficiencies of the visualization ofthe 4D CAD model and proposes improvements. The presentation abilities of the existing 4D CADmodel are analyzed and compared with the other conventional methods, namely Gantt chart, networkdiagram, and calendar. Four aspects of the visualization are addressed, namely the overview of aschedule, the duration of an activity, the relationship of an activity, and the project progress tracking.The proposed improvements employed different visual properties of 3D CAD objects such as color,line weight, and line type to represent the different activities’ performing statuses. This developmentcan enhance the visualization of the 4D CAD model and provide a more informative construction schedule.It is anticipated that the 4D CAD model with these enhancements can substitute for conventionalpresentation methods of a construction schedule.

Keywords: 4D CAD Model, visualization, construction planning, schedule, simulation

Introduction

Planning and control are important tasks forsuccessfully managing construction projects. Aplenty of information, regarding the descriptionsof what tasks to be done and when, is generatedat this stage. Currently, there are manypresentation methods to deliver this informationto users such as the Gantt chart (or bar chart),the network diagram, and the calendar. Thepresentation method of construction schedulecan heavily affect the comprehension of users.

It is also a necessary tool for communicationand collaboration among the project team.The 4D CAD model is an innovative methodof presentation (Cleveland, 1989). It isthe integration between 3D CAD objectsrepresenting construction activities and theirscheduled time (3D + time). It simulates andvisualizes the construction scenes in a timesequence. The result is a movie or an animationwhich simulates the construction components

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114 Informative Visualization Method of 4D CAD Model

adding up as planned sequences from the projectcommencement to completion. The 4D CADmodel helps create a conceptualization andcomprehension of construction processes andworking space required (McKinney and Fischer,1998). Kamat and Martinez (2001) used a 3Dvisualization technique to simulate constructionoperations for a design purpose. The 4D CADmodel, however, still has some limitations onimplementation. These limitations are tedioustasks such as 3D CAD modeling, and linkingbetween 3D CAD objects and constructionactivities; lack of document reporting formats;and deficient visualization. This research aimsto improve the 4D CAD model and overcomeits limitations on the visualization issue.

A construction schedule contains a varietyand plenty of information which mainly is thedescription of what is to be done and when.Many schedule presentation methods havedifferent abilities for presenting this informationto the users. Although the 4D CAD model hasan outstanding ability for presenting constructionactivities in visual 3D, it has some weaknesses.This paper addresses four deficiencies on thevisualization such as the schedule overview,activity duration, relationship, and projectprogress tracking. Unless these limitations areovercome, the 4D CAD model cannot entirelybe a substitute for the conventional schedulepresentation methods i.e. Gantt chart, networkdiagram, and the calendar. It is being used asa supplement to the conventional schedulepresentation methods. Users who use the 4DCAD model still need to work with otherschedule presentation methods. Therefore, itadds a lot more work for the users.

This research addresses on the visualizationof the 4D CAD model technique. It aims toenhance the visualization and to improve thepresentation ability of the technique. Theenhancements of the 4D CAD model aredesigned and the prototype is developedand evaluated. It systematically manipulatesthe visual properties of the 3D objects torepresent the specific meanings. This helpsusers to effectively and efficiently perceive moreinformation of construction plans. It isanticipated that these improvements will helpcomplete the visualization of the 4D CAD model

and encourage the use of this method morewidely.

Reviews of the 4D CAD Model

In practice, construction schedules and drawingsare created at different times by different people.Construction schedules provide informationabout time aspects and activity relationships.Drawings are normally prepared in twodimensions. They provide graphical informationof building components and scopes ofconstruction activities. Construction teamsuse both of these information sources tounderstand and execute their work. However,this understanding occurs by individual implicitinterpretation. They could understand differentlyor misunderstand. This leads to collaborationproblems and conflicts on sharing resources. The4D CAD model can overcome these problemsbecause it bridges the two separate informationsources. It helps create explicit visualperceptions. It can be an effective collaborationmedium for construction teams.

Figure 1. The development procedure of the4D CAD model

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115Suranaree J. Sci. Technol. Vol. 16 No. 2; April - June 2009

The 4D CAD model can be generallydeveloped using the following procedure(Figure 1): prepare 3D CAD model fromthe 2D CAD drawings, arrange a constructionschedule, link 3D CAD objects withconstruction activities through linking keys(e.g. activity name, layer), and create asimulation control and a visualization. Kooand Fischer (2000) studied the feasibilityof implementing the 4D CAD model oncommercial construction projects. They concludedthat it is a potential tool to accelerate theunderstanding of construction work. It helpsdiscover errors, omissions, or inconsistenciesin construction plans, and evaluate theconstructability of the planned sequences. It alsoanalyzes the congestion and accessibilityof working space. These problems are difficultto detect via a Gantt chart because constructionactivities are represented by textual names andduration bars. The 4D CAD model representsconstruction activities as virtual 3D objectswhich can effectively convey space information(Akinci et al., 2002).

McKinney and Fischer (1998) havesuggested three potential improvementdirections of the 4D CAD model, namelyconnection, analysis, and visualization purposes.Firstly, the connection purpose is theimprovement of the linking methods between3D CAD objects and the construction activitiesduring the model development procedure. 3DCAD objects can be manually selected to relatewith individual activities in a constructionschedule. This is done through programmingdialogue boxes. Dawood et al. (2002) developedan integrated database to store the connectioninformation. The database was designed usingStandard Classification Methods (Uniclass). Foranother method, proper 3D CAD objects aregrouped into different layers or blocks and laterthey are automatically matched with differentindividual activities in a construction schedulethrough the rule-based programming. Wanget al. (2004) employed a work breakdownstructure template to link with 3D CAD objects.Their 4D CAD model created a 2-way dataexchange mechanism with the schedule. Theinteractive linking method combines togetherthe functions of modeling 3D CAD objects and

arranging a construction schedule. Everycomponent that is being modeled is also linkedto a construction activity through a key identityat once.

Secondly, the analysis purpose is theimprovement in various applications. The 4DCAD model is a potentially powerful tool foranalyses and decision support. The analyticalapplications are on topics such as time,working space, sequences, and temporarystructures. The ability to simulate virtualconstruction scenes can bring awareness andforesee any error or unsuitability in theschedule. For examples, Akinci et al. (2002)applied the 4D CAD model on the congestionof working space; Chau et al. (2005) appliedit for the construction site and resourcesmanagement; Ma et al. (2005) used it forplanning site layouts at different constructionstages; Jongeling and Olofsson (2007) proposeda location-based schedule method which can beenhanced with the 4D CAD model to improvethe work-flow of construction activities.

Lastly, the visualization purpose is theimprovement of the model presentation as anenlightening information medium. Additionalannotations, graphics, symbols, colors, and textsare employed to give more necessary scheduleinformation. They can be presented in aneasy-to-interpret format. They help users obtaina quick and thorough comprehension. Forexample, different colors can distinguishdifferent activities’ performing statuses such asnot-started, in-progress, or finished. They canalso distinguish critical or non-critical activities.3D CAD objects of temporary structures andequipment are added to simulate a morerealistic construction scene so that users canexperience the coming work before it starts. Theprevious research emphasized the first twoimprovement directions while the improvementof visualization is still lacking and notreceiving attention. On the other hand, anappealing and informative visualization ofthe model should contribute to a morewidespread use of the 4D CAD model. It couldfinally become a standard method of schedulepresentation. Thus this research addresses onthis purpose.

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Conventional Presentation Methodsof Construction Schedules

A construction schedule communicates a lot ofinformation regarding the construction projectand activities. A construction team uses a planto understand and collaborate on their work. Theimpressiveness of the schedule and informationshown can help the team to perceive all thisinformation rapidly and correctly. A fewpresentation methods of construction plans arecommonly used. They are reviewed as followsand this review will give a reference forcomparison with the presentation of theexisting 4D CAD model. The review also showsthat there is no perfect presentation method.Every method has its own advantages anddisadvantages. The advantages of these methodswill be used to direct the improvements.

1. A network diagram (precedencediagram) is a presentation method that uses abox to represent a construction activity. The boxis divided into sub-boxes used for differentpieces of information such as activity name,duration, earliest start and finish time, latest startand finish time, total slack, and free slack.A pair of boxes is linked together with an arrowto represent a relationship. This arrow canrepresent many types of relationships such asstart-to-start, finish-to-start, finish-to-finish, andspecial relationships with lag or lead time. Manyof these boxes and arrows are connected to forma network.

A strong advantage of the networkdiagram is that it can clearly present complexrelationships of construction activities. It clearlypresents the identity of construction activitiesthrough individual boxes. The layout of the boxcan be used to present many types of information.Also, it assists a manual calculation of thescheduling process or the CPM. Although thenetwork diagram can show the overview of theplan, it requires a large space. A disadvantageis that the whole network of a constructionproject commonly fills more than 1 page. Mostinformation is presented in a textual formatwhich ineffectively stimulates people’s perception.

2. A Gantt chart is a presentation methodthat combines a table and a histogram. The tablepart is used to present many different pieces of

activity information. A row represents anactivity while many of its columns are used forthat activity information. Each activity has itsown bar to represent the performance schedule.The length of the bar represents the activity’sduration. In addition, arrows are used toconnect between these bars to represent theactivity’s relationships.

The Gantt chart is a very commonly usedmethod. Its strong advantages are that it clearlypresents the identity of activities; it can presentmany pieces of activity information the same as,or more than, the network diagram does; it canalso present the work breakdown structure ofthe project and group levels of activities; and itcan visualize the planned duration of an activitythrough its bar length. Another set of bars canbe added beneath the original baseline bars topresent the actual-done schedule of activities.In addition, the Gantt chart can be used for thepurposes of tracking progress. It can visuallycompare the planned against the actual-doneschedule. It is in a compact size with a neatlyorganized table and chart formats. It can givea good overview of the plan. However, itambiguously and confusingly presents theactivity’s relationships because the arrows areusually overlaid on each other.

3. A calendar is a presentation methodthat employs an ordinary calendar formto present to-do activities. An activity isrepresented by a bar. The activity bar iscontinuously drawn to pass through theperforming dates as planned. A few textualdetails of the activity can be placed within thebar.

A strong advantage of this method is thatit clearly shows what activities must beperformed on any particular date and howmany days are assigned to do an activity. Thispresentation is tidily organized but its size willnot be compact if the project is taking a verylong time. It is unable to present the activity’srelationships.

Deficiencies of the Presentation of the4D CAD Model

The 4D CAD model has been developedby many different researchers; however, there

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are some common characteristics of thevisualization. The model runs the simulationfrom the project commencement to theompletion. At the beginning of the simulation,the result screen is empty. Then, the modelgradually displays construction componentsin relation to the scheduled sequence. At anysimulated construction stage, the model showsonly components which are related to ‘finished’and ‘in-progress’ construction activities. 3DCAD objects of these components are set to‘Show’ status (meaning display on the screen).The model does not show the other componentswhich are related to ‘not-started’ activities and3D CAD objects of these components are set to‘Hide’ status (meaning off-display on thescreen). At the end of the simulation, the modeldisplays the whole building’s components.

One difference in the visualization of theexisting developments is the use of 3D CADobjects’ colors. Some developments (McKinneyand Fischer, 1998; Wang et al., 2004; Chauet al., 2005) used various colors for differentactivities or component types. They also allowedusers to customize the objects’ colors. Others(Sriprasert and Dawood, 2002) used twodifferent objects’ colors to distinguish theperforming statuses of the construction activitiesinto ‘in-progress’ or ‘finished’. The newly added3D CAD objects were assigned with the colorred which represented in-progress activities.When these activities were completed, the modelturned their 3D CAD objects to the color greenwhich represented finished activities. They alsoused the 4D CAD model to present the baselineschedule and the tracking schedule but thesesimulations ran on separate occasions.

The existing developments also have somedifferences in the user interface. The 4D CADmodel requires integration between designand planning information. The user interfacesof the developed systems were based on thecommercial 3D CAD and planning softwaresuch as AutoCAD and MS Project. Users hadto switch between the two software applicationsto obtain all information they wanted. However,some developments had their own interface.McKinney and Fischer (1998) developed aprototype system in the AutoCAD environment.

They combined the network diagram view withinthe 4D model’s result screen. Chau et al. (2005)used separate interfaces for the 4D CAD andthe schedule. They also developed the templateWork Breakdown Structure (WBS) system tobe a bridge between the 3D CAD model andthe schedule (Wang et al., 2004). Chantawitet al. (2005) used textual annotations togive appropriate safety information for theconstruction activities. They developed aseparate interface from the 4D CAD for thissafety information. The safety library and safetyplan were stored in a database that wouldsupport their system.

The 4D CAD model presents aconstruction plan via an animation. It simulatesvirtual construction scenes and processes in 3Dgraphics. Strong advantages of this method arethat it gives a percipient visual work scope andsequence. It can give a virtual experience of thework to the team. However, the visualization ofthe 4D CAD model is still unable to present allthe information of a construction plan.Compared with the conventional presentationmethods reviewed above, four deficiencies ofthe 4D CAD model are delineated. Table 1summarizes a comparison of the presentationabilities of the available methods.

1. The overview of a schedule – the 4DCAD model presents a schedule in a movieformat. The playback of the movie is runningcontinuously. The simulation of the 4D CADmodel runs by means of gradually adding up(displaying on the screen) a new group of 3DCAD objects which are representing thecommencing activities. Users will see any scenein just a moment and then it keeps changing.They cannot see the overview of a schedule.Therefore, they tend to perceive the sequencerather than the overview of the project work.Unlike a still picture medium such as a Ganttchart, users can see the whole page all the time.They can read line by line or quickly scanthrough it or skip back and forth. They canbetter conceptualize the whole content of theschedule. When the project is large andcomplex, the overview of the schedule can helpto efficiently comprehend the whole scope ofthe project work.

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2. Activity duration – the activity durationis not directly presented in a quantitative manner.The duration of an activity is interpreted via thelength of simulation time. It is the time for whichits corresponding 3D CAD objects stay in the‘in-progress’ status. For example, if the colorred is used to represent the in-progress status(Sriprasert and Dawood, 2002), an activitywhich can stay red longer has a longer duration.It is difficult to evaluate and compare thedurations of activities, particularly when theproject is large or the activities have verydifferent start times. On the other hand, the Ganttchart can illustrate the activity duration via botha length of bar and a number. The activityduration is important information of theschedule. It helps users justify the reasonablenessof the schedule and the difficulty of an activity.

3. Activity relationship – the 4D CADmodel cannot directly present the activities’relationships. There is no arrow used.Relationships are presumably interpreted via thesequence of the activities’ appearances. The startof an activity occurs right after the finish ofanother activity or the status colors of the twoactivities change synchronously. These couldmean the finish-to-start relationship of these twoactivities. However, two activities which haveadjacent performing time need not to be relatedtogether. Also, the distinction between apredecessor and a successor is difficult toperceive. The other types of relationships such

as start-to-start, finish-to-finish, and relationshipwith lag or lead time are even more difficult tobe presented via the 4D CAD model.

4. Project progress tracking – during theactual construction, a plan is used for trackingthe project progress. The Gantt chart employstwo different sets of bars to visually comparebetween the planned and the actual-doneschedules. The network diagram uses morespace within an activity box to present theactual-done data. Despite those, the 4D CADmodel is still lacking a certain method for thispresentation purpose. Its application is restrictedto only the planning phase. Sriprasert andDawood (2002) used the two separate sets ofschedule data to create two distinct 4D CADsimulations; however, it is difficult to perceivethe variances between the two schedules.

Proposed Enhancements andPrototype Development

A prototype of the 4D CAD model is developedon a residential condominium project. Themodel development followed the procedureshown in Figure 1 and described in this section.The 3D CAD is modeled using the Autodesk’sAutoCAD 2007. The 3D model is developedfrom the available 2D drawings. Some detailsof the building are excluded and simplified tosuit the research work. The schedule is preparedusing the Microsoft Project 2003. The 3D CAD

Network GanttExist.4D

Presentation abilitiesdiagram chart

Calendar CADmodel

Overview Fair Good Fair None

Activity Identity and Scope Fair Good Fair Fair

Activity Duration Fair Good Fair Fair

Relationship Good Fair None None

Project Progress Fair Good None None

Construction Sequence Fair Fair None Good

Remark: distinguishing abilities into three levels as Good – Fair – None

Table 1. A comparison of abilities of different presentation methods

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objects are linked with the correspondingconstruction activities through the linking keys.The ‘Handle’ property of 3D CAD objectsis used as their referencing identity. TheHandle of an individual object is a unique andpersistent combination of characters. Thedeveloped prototype has a total of 838 3D CADobjects representing the whole constructionproject. Their Handles are retrieved, transmitted,and correspondingly recorded in the ‘Text13’property of activities. The ‘Text13’ provided inthe MS Project is a read/write text associatedwith an individual ‘Task’ (or a constructionactivity). Since both AutoCAD and MS Projecthave supported the Automation interfaces andhave a Component Object Model (COM), aVBA code can be programmed within theAutoCAD to create an ActiveX object of theMS Project application. As a result, every 3DCAD object in the AutoCAD has its associatedtask in the MS Project. The simulation controlof this 4D CAD prototype is developed usingVBA and AutoCAD’s object model. Thevisualization is exhibited within the AutoCADwhile the corresponding schedule information

is simultaneously retrieved from the MS Projectthrough the linking keys. Figure 2 shows thelinkage concept for the model development andthe objects’ properties of both applicationsutilized in the development.

This research proposes some improvementsaccording to the deficiencies addressed in theprevious section. Graphic and textual annotationsand various colors of 3D CAD objects are employed to enhance the presentation abilities ofthe 4D CAD model. Some visual properties of3D CAD objects i.e. Color, LineType, andLineWeight are used for representing manydifferent performing statuses of a constructionactivity. Some schedule information of anactivity is used for the visualization and thesimulation control of the developed 4D CADmodel i.e. Duration, WBS, WBSPredecessors,Start, Finish, BaselineStart, BaselineFinish,ActualDuration, ActualStart, Actual Finish,PercentComplete, StartVariance, and FinishVariance. Also, additional interfaces are used toprovide some retrieved schedule informationwithout switching between AutoCAD and MSProject Applications. This schedule information

Figure 2. The created linkage between a 3D CAD Object and a construction activity, andtheir objects’ properties utilized

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complements the understanding of the users. Itis anticipated the improved model will completesome missing information of the schedule.The proposed improvements are explained anddemonstrated below.

1. The overview of a schedule is presentedwith the display of all the construction’s objectsthroughout the simulation. At the beginning ofthe simulation, all 3D CAD objects are displayedin a dark color such as grey which is similarto the background color (i.e. black). Thesegrey color objects represent the ‘not-started’construction activities. Then, the color of theobjects is gradually and sequentially changedaccording to the activity’s performing status.This is to replace the method of hiding anddisplaying the objects. All 3D CAD objects aredisplayed in the 3D-Wireframe visual style. Thisvisual style uses lines and colors to representevery object’s boundaries. Hence, users can seethe overview of the construction work at all thesimulated time. Figure 3 shows a snapshot ofthe simulation of the progressing project. Allconstruction components are shown but they arein different colors. The higher tower zone, wallsand windows are grey. It means that they are apart of the construction project but have not yetbeen started. Users can be aware of the work

content and context of the project. They canevaluate more efficiently whether the seenconstruction sequence is appropriate. They canbe consistently reminded of the remaining workand also the completed work.

2. The activity duration is presented withadditional interfaces. A Dialogue Box named“Activities in Progress” is used to present someimportant information of the in-progressactivities. The in-progress activities which arethe focus of attention are provided with moretextual information. This explicit information issuch as a WBS code which represents the uniqueidentity of an activity. The duration in a unit oftime (day) and its percentage of the total projecttime are shown. Also, the graphic bar whichrepresents the length of duration is providedalongside. The predecessors are provided as theWBS codes of all predecessors of thecorresponding activity. This information in theDialogue Box changes according to the currentin-progress activities throughout the simulationtime. Figure 4(a) shows two in-progressactivities, namely activity 5.3 and 5.4 in the“Activities in Progress” Dialogue Box. Theactivity 5.3 has a 3-day duration which accountsfor 0.8% of the total project time. The activity5.4 has a 4-day duration which accounts for 1.0%

Figure 3. The construction project case demonstrating the purposed enhancements and theobject’s color scheme

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of the total project time. Both activities are alsoprovided with individual duration bars. Userscan perceive this duration information andassess the significance of these activities to theoverall project schedule.

In addition, a horizontal Slider Controlnamed “Project Timeline” is used to present theproject timeline and the progressing project time.The Slider Control shows the simulated currentdate and the percentage of the progressing time.The ticker of the Slider Control is movingforward to the completion of the project or theend of the simulation. It helps users recognizethe project duration and the time position of thecurrent progress. Users can navigate to anyparticular date as well. Figure 4(a) shows theprogressing project on the current date of 28/03/2007 which accounts for 23.3% of the wholeproject time. Users can be informed that at thispoint progress is about a quarter of the project.

3. The activity relationship is presentedwith the use of Color and LineWeightproperties of 3D CAD objects. The performingstatuses of an activity are categorized into

‘not-started’, ‘in-progress’, and ‘finished’. Thefinished activities are further separated into thosethat are predecessors of the current in-progressactivity and those that are not. Different colorsare then assigned for these categorized performingstatuses: grey for not-started; magenta forin-progress; yellow for predecessors; and whitefor not-predecessors. The in-progress activitiesand predecessors are the focus of attention andthey convey the relationship information. Boththeir assigned colors are contrasted with thebackground color and their 3D CAD objects aregiven with thicker line weights (0.4 mm.) so thatthey can be illuminated and highlighted. The lineweights of not-started and not-predecessorsactivities are assigned with a default value of0.25 mm. Therefore, any 3D CAD object willhave a normal sequence of changing colors asgrey, magenta, yellow, and white, respectively.Also, the “Activities in Progress” Dialogue Boxprovides relationship information as the WBScodes of all predecessors of the correspondingcurrent activities.

Figure 4 shows four screen shots of

Figure 4. A series of screen shots of the enhanced 4D CAD model demonstrating the changesof activities’ performing statuses

(a) (b)

(c) (d)

1 2

3 4

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different simulation time in sequence. Theyshow that the project is progressing throughsimulated time while the color and lineweight of corresponding 3D CAD objects aresequentially changing according to theirchanging performing statuses. For example,Figure 4(a) shows that the activity 5.3 (columnsgroup 2) and activity 5.4 (beams group 1) arein-progress so that their corresponding 3D CADobjects are given in magenta. The activity 5.3has a predecessor which is the activity 5.2(columns group 1) and the activity 5.4 hastwo predecessors which are the activity 5.1(external walls) and 5.2. The corresponding 3DCAD objects of these predecessors are displayedin yellow. The 3D CAD objects representingthe bottom part of the building includingfoundations and the lower tower zone aredisplayed in white so that they all are the not-predecessor finished activities. In addition tothe different colors and line weights of 3DCAD objects, textual information of activityrelationships is explicitly provided in the“Activities in Progress” Dialogue Box.

Figure 4(b) shows a screen shot of thesucceeding construction sequence. Three eventshave occurred concurrently. The first event, theactivities 5.3 and 5.4 are finished and becomepredecessors of the new current in-progressactivities namely 5.5 and 5.6, respectively. The3D CAD objects representing the activities 5.3and 5.4 now change their color from magenta toyellow and still maintain their line weight of 0.40mm. Simultaneously the second event, thein-progress activities currently are 5.5 and 5.6and they become the new highlight. The 3D CADobjects representing the activities 5.5 and 5.6now change their color from grey to magentaand their line weight from 0.25 mm. to 0.40 mm.The third event, the activities 5.1 and 5.2which used to be predecessors are now not-predecessors and lose the highlight. Theircorresponding 3D CAD objects change theircolor from yellow to white and their line weightfrom 0.40 mm. to 0.25 mm. All these changeshelp users to better perceive the relationshipsamong these activities. Figure 4(c) and 4(d) showscreen shots of the subsequent constructionsequence.

4. The project progress tracking ispresented with the use of Color, LineWeightand LineType properties of 3D CAD objects.During the construction stage, the task oftracking the project progress is carried out. Twosets of schedule information, namely baselineand updated schedules are prepared andcompared. The baseline schedule which wasoriginally prepared during the planning stageis used as a standard of a comparison. Thesimulation of the baseline schedule is implementedas stated above. The control of the baselinesimulation is the planned start and finish timesof the activities. When the project is actuallyprogressing, these planned start and finish timesof an activity could differ from the actual startand finish times. The planned time is updatedwith the actual time, resulting in the updatedschedule. Finished activities have already hadthe actual start and finish time. Therefore, thesimulation of the updated schedule uses theactual time as a control. In-progress activitiescould have a combination of the actual orplanned time. In case of not-started activities,their planned time is still used as the control. Inaddition, the “Activities in Progress” DialogueBox provides more necessary information fromthe project tracking and the schedule comparison.This information is such as start variance (SV),finish variance (FV), and percent completion(%Com.). A positive value of these variancesmeans the actual-done time is later than theplanned time, and vice versa.

To visualize the project progress tracking,the ‘in-progress’ activities are further categorizedinto ‘late’, ‘early’ and ‘as-planned’ executed.When an activity become ‘in-progress’ and ithas the actual start and/or finish time later thanplanned, it will be defined as a ‘late’ in-progressactivity. On the other hand, an ‘in-progress’activity which has the actual start and/or finishtime earlier than planned will be defined as an‘early’ in-progress activity. The object colorassigned for the ‘late’ in-progress activities isred. The color red is used to give a warningmessage to users as late activities can bringtroubles to the project completion. While ‘early’in-progress activities are less serious, the objectcolor assigned for them is green. An ‘in-progress’

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activity which has the actual start and finishtime the same as planned will be defined as an‘as-planned’ in-progress activity. The objectcolor assigned for the ‘as-planned’ in-progressactivities is magenta. The highlights for thesein-progress activities still are their thickerobjects’ line weights (0.4 mm.). To differentiatebetween the simulations of the baseline (planned)and the updated schedules, the manipulation ofthe objects’ line type is implemented. The 3DCAD objects representing the in-progressactivities of the baseline schedule have the‘Continuous’ (solid) line type while the ones ofthe updated schedule have the ‘Hidden’ (dash)line type.

Figure 5 shows the simulation of theupdated schedule of the example project. Itshows the project progress on the simulated dateof 29/03/2007. The “Project Timeline” SliderControl shows the status date on 30/03/2007which is the date of the latest updated information.This information can be retrieved from the MSProject application’s Project property namedStatusDate. The “Activities in Progress”Box shows additional quantitative trackinginformation, namely SV, FV, and %Com. Theactivities 5.3 and 5.4 are currently in-progress.The activity 5.3 started 1 day later than plannedand it will be finished two days later thanplanned. It currently has a 25% completionprogress. The activity 5.4 started and will befinished as planned. It currently has a 50%completion progress. This visualization helpsusers evaluate the actual construction performance

Figure 5. The enhanced 4D CAD model for the project progress tracking

compared with the baseline and obviouslydetect the problem areas. Users can be aware ofthe late activity and assess its impact. They alsocan be informed about the number of days late.

Evaluation Results

The application of the prototype of the 4D CADmodel showed that the proposed enhancementscould help users effectively perceive all necessaryschedule information on the visualization. Userscould gain visual perception and experience ofnot only the construction sequence but also theconstruction schedule which was presentedin four aspects, namely the overview of theschedule, the activity duration, relationship, andthe project progress tracking. These aspects areas important as the construction sequence. Theoverview helps remind users of the contentand context of the whole project work. It alsopersistently shows what has been done and whatis remaining. The duration and relationshipindicate the significance of an individualactivity. They enable users to assess the sensibilityof these planned values. Lastly, this enhanced4D CAD model recognizes both the baseline andupdated schedules so that it can be used for theproject progress tracking purpose. This extendsthe usefulness of the 4D CAD model to coverboth planning and construction phases.

A methodology of these enhancementswas developed in this study. The performingstatuses of a construction activity wasmeticulously categorized into ‘not-started’,

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‘as-planned in-progress’, ‘late in-progress’,‘early in-progress’, ‘predecessor-finished’, and‘not-predecessor-finished’. These various statuseswere used to express schedule overview, activityrelationship, and project progress tracking.Visual properties of 3D CAD objects such ascolor, line weight, and line type were employedto represent the different activities’ performingstatuses. The distinct combination of color, linethickness, and type could give different levelsof emphasis and highlight on constructionactivities. Additional interfaces such as dialogueboxes were used to provide the other necessaryschedule information including activity duration,relationship, and project progress tracking.

Despite these abilities, some limitationsof the enhanced 4D CAD model and possibilitiesare recommended for future research studies.The visualization of the 4D CAD model displays3D CAD objects on screen that are clusteredinto groups of different colors. The identity andscope of each individual activity are difficult todistinguish. Although special relationships ofconstruction activities including start-to-start,finish-to-finish, lag, and lead time could bevisualized and provided via the enhanced 4DCAD model, they may not be clearly distinguishedfrom a common finish-to-start one. Otheractivities’ statuses such as critical and non-critical or some filtering features can also befurther developed on the 4D CAD model usinga similar methodology. Other features ofplanning and scheduling can be included in theCAD application so that the development ofthe 4D CAD model can be independent fromthe scheduling application. The future CADapplication will become a complete integratedworking station for design, drafting, planning,and visualizing. Moreover, many forms ofmultimedia including sounds, texts, still, andmoving pictures have great potential to presentcomplete schedule information without requiringthe conventional schedule presentation methods.A proper combination of these can create animpressive presentation through the 4D CADmodel.

Conclusions

The 4D CAD model is a novel presentation

method of the construction plan. It shows asuperior capability to the conventional schedulepresentation methods, namely Gantt chart, thenetwork diagram, and the calendar. It clarifiesthe construction sequence and the spatialconstraints with an unambiguous visualperception. It results from the integration ofdesign and planning data. Also, it conforms tothe present trend of development that focuseson the parametric 3D design and drafting, thedata integration of the whole project’s life, andthe building information model (BIM). The useof the 4D CAD model is anticipated to bewidespread in the near future.

This paper addresses on the presentationdeficiencies of the existing 4D CAD model. Itproposes some enhancements for this method.These proposed enhancements draw on theadvantage analysis of the conventionalschedule presentation methods. The four aspectsof the visualization were addressed, namely theoverview of the schedule, the activity duration,relationship, and the project progress tracking.The prototype of the 4D CAD model wasdeveloped using AutoCAD and MS Projectapplications. The enhanced 4D visualizationexhibits in the AutoCAD environment, whilebeing supported with schedule information fromMS Project. This integration was programmedwith VBA code using the Automation andActiveX object technology. The manipulationand control of visual properties of 3D CADobjects was also programmed with VBA codeusing Component Object Model (COM). Thisenhanced 4D CAD model is anticipated tofulfill its presentation ability so that it couldfinally become a standard method.

Acknowledgment

This research is funded by The Commission onHigher Education and The Thailand ResearchFund (MRG5080271).

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