TOPOGRAPHIC INFORMATION IN CULTURAL AND NATURAL HERITAGE VISUALIZATIONAND ANIMATION

Boehler, W.1) , Heinz, G.2), Scherer, Y.1), Siebold, M.1)

1) i3mainz,Institute for Spatial Information and Surveying Technology, FH Mainz, University of Applied Sciences,

Holzstrasse 36, 55116 Mainz, Germany, Phone +49-6131-2628-27, Fax +49-6128-2628-15i3mainz@geoinform.fh-mainz.de

2) Roemisch-Germanisches Zentralmuseum, Forschungsinstitut für Vor- und Fruehgeschichte,Ernst-Ludwig-Platz 2, 55116 Mainz, Germany

KEY WORDS: Cultural heritage, cultural landscapes, landscape visualization, 3D modeling.

ABSTRACT: Cultural heritage objects can only be understood, if the surrounding landscape is takenunder consideration, too. In certain cases, the landscape even constitutes the cultural object itself.UNESCO has considered this fact by adding the category of 'Cultural Landscapes' to the sites eligible forthe World Heritage List. In this paper, methods to survey, document and visualize landscapes arediscussed. Especially, with new imaging opportunities, such as satellite images with 1 meter resolution,landscapes can be mapped economically. Results, such as maps, perspectives, animations andgeographic information systems can help to present the landscapes to those who cannot visit its locationand are a powerful means for studying, monitoring and managing landscapes of cultural relevance.

LANDSCAPES

Natural Features, Formations and Sites

UNESCO (1972) uses the term 'Natural Heritage' for physical, biological, geological and physiographicalfeatures, formations and sites of outstanding value from an aesthetic or scientific point of view. Far morethan 100 natural heritage sites are designated by UNESCO as World Heritage and many others arereceiving various degrees of protection under state or local legislation. From a conservationist's point ofview, it would be desirable to keep human interference completely away from these areas. Since, on theother hand, many visitors are attracted, management guidelines have to be prepared and enforced and amonitoring process is needed to detect and prevent unwanted changes. Nevertheless, natural features,formations and sites are subject to changes caused by nature itself (UNESCO Operational Guidelinesspecifically mention on-going geological processes and on-going ecological and biological processes)and it would be a misinterpretation of conservation to keep these natural processes away from theobjects.

Cultural Heritage Objects and Landscape

Meanwhile, more than 600 objects of 'Cultural Heritage' are designated by UNESCO as World Heritagesites. This is just a choice selection of a heritage comprising innumerable single monuments, groups ofbuildings or historical and archaeological sites of outstanding value for historical, artistic or scientificreasons. Although cultural objects are man-made, UNESCO in its Convention mentions landscape in thiscontext, too ("buildings because of their ... place in the landscape", "combined works of nature andman").

In fact, no cultural heritage object can be understood without taking the surrounding landscape intoaccount. Human dwellings have to use places in the landscape where an optimal protection from naturalforces (weather, flooding) and enemy attacks is possible, and the supply of essentials (food, water,kindling) is assured as well. Special topographic features are chosen in all religions as places of worshipor as sites for the location of divine buildings. Sovereigns chose special places to erect their palaces andmausoleums and often changed the surrounding topography, too. Cities developed along trade roads orclose to bridges and fords. And even when a small arrow tip is found somewhere in the fields it should bestudied why it was lost here and not somewhere else in the landscape.

The location of all those objects in a landscape was a result of practical or metaphysical considerationsand rules. Thus, it is not sufficient to examine and document the object itself. Far more often thanpresently done, the landscape surrounding a cultural heritage object should be considered, studied and

documented, too. If the present topography is surveyed, mapped and visualized, historic evidence maybe used to reconstruct landscape development from ancient to present times. At the same time,conservational hazards originating from the present topography (erosion, slides, flooding) or landuse(agriculture, industry, traffic) can be foreseen and possibly prevented.

Cultural Landscapes

There are cases where natural and cultural criteria of a landscape cannot be separated. The value ofsuch landscapes, being both, of natural and cultural significance, was hard to define with the 1972UNESCO Convention. This is why UNESCO revised it in 1992 and adopted three categories of ’CulturalLandscapes’ (Roessler, 2000):

Landscapes Intentionally Designed and Created by Man. This embraces garden and parklandlandscapes constructed for aesthetic reasons. Often, but not always, buildings and ensembles are part ofthose landscapes.

Organically Evolved Landscapes originate from an initial imperative (social, economic, administrative,religious) and have developed their present form in an evolutionary process in close interdependencewith the natural environment. This evolutionary process may have come to an end in the past (’relict’ or’fossil landscape’) or it is still continuing (’continuing landscape’). Where a relict landscape needsconservational methods to preserve the site, a continuing landscape needs management plans andmeasures to allow evolution without destroying its outstanding value.

Associative Cultural Landscapes may show no man-made evidence at all (thus, from a materialisticpoint of view just being natural landscapes), but powerful religious, artistic or cultural associations of thenatural element attach special importance to those landscapes.

LANDSCAPE DOCUMENTATION

Virtual Landscapes

A landscape can only be experienced in all aspects when visited at its original location. Obviously, novirtual landscape can match reality. It should be noted, however, that not everybody is physically orfinancially able to visit any landscape of interest. Many landscapes can only be reached after a strenuousjourney. Other places are located within areas of war or turmoil and - unfortunately - one has to beprepared that this may happen to places that have been safe so far, too. In these cases, a virtual tripthrough a digitally created landscape can be the only way to explore an area.

A person, moving on the surface of a landscape, can overlook only a very limited part of this landscape.Many impressive landscapes (e.g. a river winding through a mountain range) can only be observed intotal from locations far above the ground. Even when such viewpoints can be reached by airbornevehicles, the vision will be limited by the vehicle’s structures as well as atmospheric effects. Virtuallandscapes do not impose any limits to the observer in this respect because any observation point canbe reached to have a look at the scene and virtual trips through and around the place at a course ofone’s own choice can be undertaken. These are reasons why a virtual representation is of much more

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Fig. 1: Combination of a DEM and a map to produce a perspective view of apart of the Rhine River valley (Emmel 2000).

importance for the documentation of landscapes as compared to virtual images of other objects ofcultural heritage.

Digital Elevation Models and Texture Overlays as Elements of Virtual Landscapes

A landscape documentation can just be an abstraction of the real world. No matter which method isused, only a selection of the landscape’s features can be surveyed, recorded and visualized. In order todescribe the morphologic features of a landscape, elevations of single points are recorded. This data set,where spot elevations are attached to selected vertices are referred to as Digital Elevation Model (DEM).It may consist of single raster points arranged in a regular grid pattern, single points in an irregularpattern (e.g. from tacheometric measurements) or contour lines (from existing maps). Since elevationsfor points between these data have to be interpolated, there should be enough points in the DEM todescribe the topographic surface adequately. If sharp edges are present, the DEM should include breakline information to avoid smooth interpolation across these lines.

To give information about the features covering the topographic surface, a texture image has to bedraped over the DEM. Raster type images photographed with digital cameras or scanned from maps orphotographs can be used (Fig. 1). As long as this image is presented in vertical parallel projection, asimple map type 2D representation of the landscape is achieved. Shading may help to experience thethird dimension; contour lines are more precise but not as easy to conceive. If all data are available indigital form, perspectives can give a much better impression of the landscape and its topography (Fig. 2).Animations with smoothly changing relative positions of camera and landscape result in a better three-dimensional perception and allow a good interpretation.

Surveying and Imaging Techniques

Digital Elevation Models can be derived by several different methods. For detailed DEMs, tacheometricsurveys or stereophotogrammetric measurements from aerial photographs should be used. Larger areascan be surveyed using aerial photographs of smaller scale or even GPS measurements. Some Earthobservation satellite sensors supply images suitable for stereoscopic vision by taking images from twodifferent locations of an orbit, looking forward and backward towards the same ground location (in-trackstereo) or by taking images from neighboring orbits (across-track stereo). These images from digitalsensors or scanned photographs allow automatic DEM generation by matching techniques, thus

supplying a very powerful andeconomic method to createDEMs for large areas.

Texture overlays are alwaysneeded in raster format.Nevertheless, vector informationfrom maps, plans CAD or GISsystems can be used if scannedor converted to raster data (Fig.1). Scanned aerial photographsor digital satellite images areideally suited to generateoverlays (Böhler et. al. 1997,1999). Their potential has hardlybeen recognized anywhere incultural heritage documentation.In the meantime, raster datawith one meter pixel size areprovided (SpaceImaging 2000).So, textures of high quality canbe used (Figs. 2, 3 ), even whenaerial photographs are notavailable.

Fig. 2: Perspective view showing a part of a Tang emperor’s mausoleumin Shaanxi, China. IKONOS data have been draped over a DEM derived

from a local tacheometric survey. Vector data from archaeologicprospecting (findings, tumuli, location of an ancient wall) are

superimposed.

Accuracy of data can become a critical issue when different data sources have to be combined. All datahave to be geo-referenced in the same coordinate system. Small scale maps, for example, showintended displacements when several symbols are very close together. Therefore, map information maynot coincide with other information (see railway line at the left valley side in Fig. 1). If high resolutionimages are used, the information intended for combination has to be of corresponding accuracy. In thecase of one meter IKONOS satellite images, we found out that the DEMs previously used with LANDSATand SPOT images did not have sufficient quality.

Geographic Information Systems

Geographic Information Systems (GIS) are an ideal means to manage data of cultural landscapes orcultural heritage objects in landscapes (Heinz 1997). Quite a few World Heritage landscapes and objectsare already documented (and managed) using GIS-techniques (Roessler 2000). Special guidelines forthe use of GIS in cultural resources management were developed (UNESCO 1999). A GIS provides toolsto store, manage, analyze and visualize spatially related data. If a GIS with a temporal dimension ischosen, the evolution of a cultural landscape can be modeled and studied. Also, future developmentsand planning alternatives and their consequences can be explored in the same way.

Mapping and Visualization Techniques

If information is available in digital form, any combination of data can be visualized in any views andscales necessary for the observer. Vector maps or orthophotos can be shown separately or as acombined product. If combined with the DEM, virtual views from any observation point on the surface orabove can give an imagination of a present, past or future landscape (Fig. 2).

Not every relevant detail can be seen in images, however. Cultural heritage objects may be too small,covered by soil or vegetation, or even removed for conservation or museum presentation. To show thoseobjects, 2D- or 3D-symbols can be generated and stored in separate overlays. If included in a multimedia

Fig. 3: Comparison of different satellite image resolutions.

(From Böhler, Heinz 1999, complemented with an IKONOS image). Upper row from left to right: IKONOS PAN, KVR-1000, SPOT PAN Lower row from left to right: IRS-1C LISS III, SPOT XS, LANDSAT

or GIS application, thesesymbols can be switched onand off depending on thematicattributes or historical periods,and linked with further text orgraphical information (Fig. 4).

Perspective views, based onimages draped over DEMs, donot give a proper visualizationof buildings, however, sincestandard DEMs, being only 2½-dimensional, can not handlevertical surfaces and theimages do not provide thenecessary texture. Here,separate data have to beobtained. This can be a verylarge task, but the expenditurecan be reduced when onlyrelevant structures are shownand when their geometry isreduced to typical features. Forexample, for a virtual flight overa 40 km part of the Rhine River(which will be proposed as aWorld Heritage CulturalLandscape) we have producedsimplified 3D appearances formany castles and ruins whichcan be placed in the landscapemodel. They can also beconsidered as 3D symbols, andwe experiment with a virtualflight where those symbols willappear in a scale larger thanthe scale of the landscapemodel (Fig. 5).

Finally, landscape changes,caused by nature or man-made,can be modeled if multitemporalinformation is available.Consecutive images or videos,showing the historical change,

are very useful for understanding natural and cultural landscape development. Landuse changes can beshown using different overlays. If elevation changes took place (e.g. erosion or earthworks), the DEMitself has to be changed depending on time. Since appropriate tools for DEM modeling are not availablein software products, own procedures were developed and applied for a video showing the geological(mainly volcanic) and cultural (landuse changes, heavy quarrying) changes of a landscape (Böhler et. al.1999, 2000). The video is presented in the poster session of this workshop.

LANDSCAPE MANAGEMENT AND MONITORING

Considering the size and complexity of a landscape, adequate tools have to be provided for itsmanagement. After UNESCO had introduced legal instruments to recognize and protect culturallandscapes of outstanding universal value, and several cultural landscapes were included in the WorldHeritage list, it was soon realized, that "the resources management, e.g. the management and protectionof the cultural values for which these sites have been inscribed , has to be improved" (Roessler 2000). Itis obvious that surveying and mapping procedures, based on sufficiently complete and updateddatabases, are needed to document and monitor the sites and to allow predictive modeling of future

Fig. 5: 3D symbol of a castle placed in virtual landscape.Symbol is based on the real appearance of the castle andshown in larger scale than topography. (Holtkamp 2000).

Fig. 4: Screenshot from a multimedia project (Eifel, Germany).Archaeological information is linked to symbols in a virtual landscape.

developments. The role ofGeographic InformationSystems is of specialimportance in this context(UNESCO 1999).

Especially in the case of’continuing landscapes’, wherea large number of authoritiesand private owners may have toco-ordinate their actions andpolitical decisions have to beprepared and mediated,planning and modeling futuredevelopments is of utmostimportance. Changes within the

landscape or in its neighborhood may impair or even destroy its cultural value. This is why UNESCOdemands ’reactive monitoring’ and periodic reporting to ensure that World Heritage Sites remainundestroyed and can be kept on the World Heritage List.

CONCLUSIONS

Documenting cultural landscapes or landscapes around objects of cultural heritage has often beenneglected because the surveying and mapping expenditure was too high. With modern surveying andvisualization techniques, landscape documentation and visualization has become affordable andrewarding. Especially when combined with geographic information systems, virtual landscapes can be apowerful means to describe a landscape and to monitor and manage its conservation and development.

REFERENCES

Böhler, W., Heinz, G., 1999. Integration of High Resolution Images into Archaeological Documentation.ISPRS WG V/5, WG V/2 Joint Workshop, Thessaloniky. Proceedings, pp. 166-172.

Böhler, W., Heinz, G., Scherer, Y., 1997. Using Satellite Images for Archaeological Documentation. CIPASymposium Goeteborg. ISPRS Proceedings, Volume XXXII, pp. 226-233.

Böhler, W., Scherer, Y., Siebold, M., 1999. Visualization of a Landscape Genesis. ISPRS CommissionV/SIG Animation Workshop Onuma. Proceedings, pp. 9-14.

Böhler, W., Heinz, G., Scherer, Y., Siebold, M., 2001. Video Showing a Landscape Genesis. ISPRSWorkshop Ayatthuya.

Emmel, V, 2000.Virtueller Flug über den Mittelrhein. Diploma thesis, FH Mainz, unpublished.

Heinz, G., 1997. Aufbau eines Geo-Informationssystems zur Dokumentation archäologischer Befunde. -Tagungsband, 2. Geosystems Fachtagung. - Germering .

Holtkamp, B, 2000. Entwicklung dreidimensionaler Symbole für eine Virtual-Reality-Anwendung. Diplomathesis, FH Mainz, unpublished.

Roessler, M., World Heritage Cultural Landscapes. Identification, Conservation, Monitoring. ISPRSProceedings, UNESCO-ICOMOS-CIPA-ISPRS World Heritage Session. Amsterdam 2000.

SpaceImaging, 2000: www.spaceimaging.com

UNESCO 1972. Convention Concerning the Protection of the World Cultural and Natural Heritage,revised 1992.

UNESCO 1999. GIS and cultural resources management. A manual for heritage managers.

Fig. 6: Three frames from a video showing the development ofsettlements over 100 years (Eifel, Germany). Settlement boundaries were

digitized from old maps and superimposed on a recent satellite image.