Augmented reality for exterior construction applications英文精品课件

In: Augmented Reality and Wearable Computers,

W. Barfield und T. Caudell, eds. Lawrence Erlbaum Press, 2001.(Manuscript completed in 1998)

Augmented Reality for Exterior Construction Applications

Gudrun Klinker (1), Didier Stricker (2), Dirk Reiners (2)

(1) Technische Universit?t München,

Lehrstuhl für angewandte SoftwaretechnologieArcisstr. 21, D-80290 München

(2) Fraunhofer Projektgruppe für Augmented Reality am ZGDV,

Rundeturmstr. 6, D-64283 Darmstadt, Germany

Abstract

Augmented reality (AR) constitutes a very promising new user interface concept for many applications. In thischapter, we pay particular attention to developing AR technology for exterior construction applications,augmenting video sequences from construction sites with information stored in models. Such augmentations cantremendously benefit several business processes common to many construction projects.

We are focussing on two approaches to augment the reality of construction sites. The first one augments videosequences of large outdoor sceneries with detailed models of prestigious new architectures, such as TV towersand bridges. Since such video sequences are very complex, we currently pre-record the sequences and employoff-line, interactive techniques. The second approach operates on live video streams. To achieve robust real-timeperformance, we need to use simplified, “engineered” scenes. In particular, we place highly visible markers atprecisely measured locations to aid the tracking process.

1 Introduction

Augmented reality (AR) constitutes a very promising new user interface concept for many applications.Currently, we pay particular attention to developing AR technology for exterior construction applications. In thecontext of the European CICC-project [10], we develop and evaluate the potential of AR in a series of pilotprojects, augmenting video sequences from construction sites with information stored in models. Suchaugmentations can tremendously benefit several processes common to many construction projects.-

Design and Marketing: Creating a design and evaluating it for function and esthetics, and showing acustomer what a new structure will look like in its final setting. AR provides the unique opportunity tointegrate the design into the real world context.-

During Construction: Visualization whether an actual structure is built in accordance with the design;quick update of work plans after a design change; visualization of consequences of potential design changesbefore they are agreed upon.-

Maintenance and Renovation: Visualization of hidden information (wires, pipes, beams in a wall);visualization of non-graphical information (heat and pressure of pipes, maintainance schedules and records);visualization of potential redesigns (interior, exterior) to evaluate their compatibility with existing structures,and placement of new structures onto/into preexisting buildings.

Some of these benefits can also be partially achieved with other graphical approaches, such as Virtual Realitypresentations. The level of realism, however, that can potentially be achieved with AR-systems far surpasses VRwhich seems to asymptotically narrow the gap between synthetic models and the real world (see Figure 1). AR,on the other hand, starts with the real world, augmenting it as little or much as is deemed suitable for the task athand [35].1

1

Sources of all graphical maerial are listed at the end of this chapter.

realismAR1.0VRtimeFigure 1: Potential Realism of AR vs. VR approachesThis gain in realism is coupled with a potential gain in speed since the real environment doesn’t have to berendered but merely mixed with a (much smaller) virtual model. The price to pay is the effort to strive forperfect alignment between the real and the virtual world. Assuming that this can be achieved satisfactorily inreal-time in the foreseeable future, the overall speed gain by not having to synthesize the real world will beconsiderable.

1.1 AR challenges and chances in exterior construction applications

Exterior construction applications impose very demanding challenges on the robustness and usability of evolvingAR technologies.

- First of all, the mere size of a large construction project (e.g., a bridge, a tower, a shopping mall or anairport) is overwhelming. The synthetic data is huge and needs special processing technology. To presentsuch wealth of information in real time, the data needs to be reduced and simplified. Concepts such as levelof detail and relevance need to be developed with respect to the task at hand. Furthermore, muchinformation is currently only represented in two dimensions. Tools to translate it into a three-dimensionalcontext are necessary. To access all data when and whereever necessary, the system depends on a very goodcomputer infrastructure, including fast and mobile networks, computers, and data repositories.

- Second, the size of not just the synthetic data model but also of the real site imposes problems. Usersmanoeuvre in a very large space. Some AR devices, such as magnetic trackers or overhead surveillancecameras are rather geared towards indoor applications and unlikely to operate well under such conditions.

GPS, on the other hand, optical tracking techniques and inertial sensors have the potential to fare well. Butthey must be able to cope with situations, when only partial information or only a local view of the entireconstruction site is available. Exterior construction scenarios thus require more tracking skills than what iscurrently shown in table-top demonstrations [55, 60, 65, 68].-

Third, AR applications require a very accurate model of the current site (a reality model) both to determinethe current camera position and to augment the current view realistically with synthetic information (thevirtual model). Realistic immersion of virtual objects into a real scene requires that the virtual objectsbehave in physically plausible manners. They occlude or are occluded by real objects, they are not able tomove through other objects, and they cast shadows on other objects. To this end, AR-systems needgeometrically precise descriptions of the real environment. Yet, construction environments are not wellstructured. Natural objects such as rivers, hills, trees, and also heaps of earth or construction supplies arescattered around the site. Typically, no exact detailed 3D information of such objects exists making itdifficult to generate a precise model of the site. Even worse, construction sites are in a permanent state ofchange. Buildings and landscapes are demolished, new ones are constructed. People and constructionequipment move about, and the overall conditions depend on the weather and seasons. AR applications thusneed to identify suitable approaches for generating and dynamically maintaining appropriate models of thereal environment.-

It is also important to decide upon the appropriate level of realism with which virtual objects are renderedinto the real world. For safety reasons, construction workers need to have and maintain a very clearunderstanding of the real objects and safety hazards around them. Virtual objects must not decreasepeople’s awareness of danger, e.g., by perfectly adding virtual floors and walls to the bare wireframe ofbeams of the next floor being built in a high-rise.

In other situations, however, the highest level of realism is highly desirable, e.g., when visualizing whether adesigned object will integrate well into an existing landscape.-

In addition to augmenting reality, exterior construction scenarios also need tools to diminish reality, since inmost cases, objects and landscapes are removed or changed before new ones are built. Thus, techniques forsynthetically removing real objects from the incoming video input stream need to be developed.

Despite such challenges, exterior construction is a very suitable application area for AR. Construction, in its verynature, is very much a three-dimensional activity. Business practices and work habits are all oriented towardsthe design, comprehension, visualization and realization of 3D plans. Workers are used to graphical descriptions

such as 2D plots. Much information is already represented and communicated in graphical form. Thus, newgraphical user interfaces like AR fit very naturally into current work practices.

Furthermore, gathering high-precision geodesic measurements of selected points on a construction site andmarking them in suitable ways is a well-established practice. Large construction sites use a wealth of highprecision equipment such as theodolytes, differential GPS and laser pointers, that AR can build upon.Engineering the environment to suit the current capabilities of the technology is acceptable within limits. Thus,AR can begin by building applications that simplify many of the general challenges, adapting the constructionsite to suit their skills. Over time more sophisticated and general approaches can be developed.

1.2 Our approach

Figure 2 illustrates our current framework for augmenting images of the real world with virtual objects. The AR-viewer takes four kinds of input (shown in the darker, rounded rectangles): virtual object models to be visualizedor rendered, a photo or an image sequence to which the virtual objects are added, camera positions to facilitateseamless integration, and a reality model to enable physically correct coexistance of virtual and real objects.Virtual Model3D measurements2D map(s)Photo(s)Video sequence3D scenereconstructionReality ModelInformationvisualizationFeature detection,Camera calibrationTrackingImage enhancement,Geometric correction,Diminished realityCameraPositionAR viewerFigure 2: Conceptual framework of an AR-system.