nautiskt 3d-gis med sikte på kognitiv avlastning och...

192 KART OG PLAN 3–2007

Nautiskt 3D-GIS med sikte på kognitiv avlastning och beslutsstödThomas Porathe

Thomas Porathe: A 3D Nautical GIS targeting Cognitive Off-loading and Decision Making

KART OG PLAN: Vol 67, pp. 192–200. P.O.Box 5003, NO-1432 Ås. ISSN 0047 - 3278

A 3D Nautical GIS system aimed at nautical navigation is proposed in this paper. The system sim-plifies navigation by adding three major features to existing chart systems: the egocentric view, al-lowing geographical data to be viewed from a bridge perspective and thereby removing the problemof mental rotations; the seaways, displaying traffic separated fairways and individual track lines,and the NoGo area polygons displaying warning areas for waters too shallow for the ship in questionin the current tidal situation.

Keywords: Navigation, wayfinding, route guidance, 3D maps, 3D-GIS

Thomas Porathe, tekn. dr., Department of Innovation, Design and Product Development, MälardalenUniversity, P.O.B. 325, SE-63105 Eskilstuna. E-mail: [email protected]

IntroductionA lot of people find map reading difficult, par-ticularly in environments where landmarksare scarce and easy to confuse. This is oftenthe case in coastal and archipelago navigationor when hiking in mountain or forest areas.When we walk in a forest where trees are highand obscure the view, we are pleased when wefind a path or a track going in the right direc-tion. This is not only because it is easier towalk on a path, but also because some of theburden of navigation will be lifted of ourshoulders. «People have walked this way be-fore» and the path will now do the navigationfor us. Man is a path follower. We make pathsand we build roads. If we ask for instructionswe get a list of instructions such as: «Go straittwo blocks, turn left after the church, thenpass the bridge…» Roads make wayfindingeasier. The ancient Romans were famous fortheir roads. They used lists for wayfindingand called them itineraries. They also listedplaces and distances such as Venta SilurumVIIII, Abone XIIII, Traiectus VIIII…1 [1].

Historians including Janni,[4], Broderssen[2] and Whittaker [8] suggest that the Ro-man empire was built on a different under-

standing of space based on road thinking.Janni calls this spatial understanding hodo-logical after the Greek word hodos, whichmeans road. They argue that very litte evi-dence of, and few references to our kind ofspatial maps are found, whereas there arefrequent references to itineraries. One of thevery few «maps» that actually has survivedas a medieval copy of a Roman original fromthe 4th century is the Tabula Peutingeriana(see Figure 1). The map is 7 meters long andonly 35 cm wide, and depicts Europe and Asiafrom Britain on the far left to India on theright.

This type of schematic map is well knownfrom modern public transportation. TheBritish graphical designer Henry Beck is of-ten referred to as the inventor when he re-vised the London Underground map in the1930’s. However, we know that maps in themodern sense existed in the antique era, forexample the maps of Agrippa and Ptolemy.But somehow the itineraries must have beenmore practical in actual wayfinding. Maybewe can learn something from this?

The first written nautical information tosurvive to our days is the peripili of the an-

1. From the Antonine Itinerary no. 14 Isca Silurum to Calleva Atrebatum over England. The itineraries consisted of names of places and the distance between them in thousands of paces. One Roman pace was a double step, about 1.4 meters, so the Roman mile (1000 paces) would be about 1.48 km.

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cient Greeks. Scylax of Caryanda wrote a setof sailing directions in the fifth century B.C.of which some fragments remain. They con-sist of lists of names and distances betweensafe havens along the coasts of the Mediter-ranean and the Black Sea [3]. The first nau-tical chart does not appear until the end ofthe 13th century. Not until the 18th centuryhas the chart become the major means ofconveying navigational information; beforethat, the hodological view of sailing direc-tions prevailed. As mentioned above, thesailing directions first appeared as lists ofplaces and distances, then incorporated geo-graphic landmarks and navigational warn-ings. In the 15th century the French pilotPierre Garcie started to add coastal views tosailing directions. These were simple wood-cuts of the coast and islands as seen in anegocentric perspective from the deck of theship (see Figure 2).

Fig. 2. A coastal view Île d’Ouessant at thewestern tip of Bretagne in France. A woodcutfrom Robert Norman’s 1590 Safegarde ofSaylers [7].

Sailing directions and coastal views are los-ing their importance today, as satellite basedsystems present accurate positions on pre-cise electronic charts. But as the speed ofships increase, decision times become short-er. More and more modern equipment crowdthe bridge and information overload becomesa problem. The need to limit the amount ofinformation and present it at just the right

time becomes apparent.Today the hodological view could be the

«just-in-time» presentation of geographicalinformation, tailored to fit the limitations ofthe human brain.

The 3D Nautical ChartHigh speed and short decision time haveplayed a major role in several accidents atsea. One problem has been related to mapreading and the inability to maintain a cor-rect situational awareness. In an informa-tion design research project at MälardalenUniversity in Sweden a 3D nautical charthas been proposed [5]. Three concepts formthe basis for the chart system: the egocentricview, the seaways and the dynamic NoGoarea polygons.

The Egocentric ViewBy tradition, geographical information ismost commonly presented to the bridge crewin an exocentric, north-up orientation. Whencomparing map information with the physi-cal world it is necessary to mentally rotatethe map to align it with the physical world.The linear relationship between the timeneeded to mentally rotate an object and thedegree of rotation needed was discovered byShepard & Metzler in 1971 [6]. The implica-tion for the mariner is that decision makingon southbound courses will be slower than onnorthbound.

The suggested solution is to allow the nav-igator to access the map database in an ego-centric perspective (see Figure 3). The ego-centric view would display a scene on the dis-play similar to what the navigator sees out-side the windows, but with the navigationalinformation added.

The chart can be viewed as simply a tradi-tional chart in an exocentric orthographic per-spective, but at any time the user can dive

Fig. 1 Tabula Peutingeriana is a 7 meters long and 34 cm wide schematic «map» of the worldf B it i t I di

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down into the chart and view it as a dynamiccoastal view from an egocentric perspective.

To allow this, land height information hadto be added to the map database. Differentprototypes have been built using elevationcontours and photogrammatically measuredbare earth elevation models, but laserscanned data have so far given the best re-sults. A 2 m by 2 m grid is used as a target

resolution for the elevation data and the ter-rain skin is draped with orthophoto with res-olution 25 cm per pixel. With this data reso-lution the visual iconicity is good enough toallow direct recognition (see Figure 4).

The SeawaysRoads are cognitive tools that facilitate deci-sion making. A secondary property is that

Fig. 3. The exocentric and the egocentric view of the 3D chart. From the authors’ pro-totype chart of the entrance to Mariehamn in the Åland archipelago.

Fig. 4. A photo from the physical world (top) and a screen dump from the same position in the3D chart (bottom). Vinga lighthouse in the Gothenburg archipelago. Photo by the author.




they provide us with a smooth surface todrive on. Once on the right side of the road,the driver is relieved of constant decisionmaking until he reaches a cross road, andonce there he is aided by road signs.

At sea, a similar system is used in trafficseparation schemes or by depicting the fair-way as a single line in the chart. Many down-loadable waypoint libraries throughout theworld use one and the same track for both di-rections. The suggestion here is to use expe-rience from land road networks and to trafficseparate all fairways, adding traffic signsdisplayed in the 3D chart as needed (seeFigure 5).

Individual track lines. Based on the routeof the individual ship separate «own ship’strack» should be displayed. These trackscould also be broadcasted from port authori-ties to approaching ships leading them to thecorrect berth, they could be used for remotepiloting and they could also be broadcastedthrough the AIS system to, together with asymbol of the ship, show other ships andtheir intended route.

The NoGo area polygonsNormally, the areas free for a ship to navi-gate have to be calculated based on thesoundings displayed in the chart, the currentdraught and squat of the ship and the waterlevel. If something unexpected should hap-pen in confined waters, this calculation hasto be done under time stress. By entering rel-evant data from on-board sensors and tidalinformation from on-line sources, NoGo are-as could be calculated in real time and dis-played in the chart system. With reliable

bathymetric data, these polygons could bedisplayed for any depth in high resolution,not just the pre-drawn depth contours of thechart (see Figure 6).

Laboratory Testing

The Experiment Setting

A laboratory experiment was designed totest the general concept of navigation usingthe egocentric view. A 6 m by 6 m large studioarea was prepared to serve as the confinedwaters of a complicated archipelago. A smallcart was used as a «ship.» Forty five subjectsdrove the cart along a designated track in thearchipelago. The track was the only allowed«navigation channel» in the otherwise «shal-low waters» where a «grounding» was regis-tered. The track could only be viewed on thechart, not on the studio floor. Some boxes, achair and a paper tube were used as visualnavigation aids (see Figure 7).

As an indoor GPS system, the position andheading of the cart was tracked by an infra-red tracking system (accuracy < 2 cm, 120Hz) which sent the data back to a laptop com-puter fitted on the cart. The various maptypes tested could be displayed on the laptopcomputer.

The Map TypesFour map types were tested (see Figure 8).

In each map the NoGo areas were marked inred and the allowed track in yellow. The fournavigational aids (two boxes, a tube and achair) were also marked. The four map typeswere:

Fig. 5. Examples of seaways, an individual track line and signs displayed in the chart.


Thomas Porathe


Fig. 6. The northern entrance to Gothenburg harbour looking west, out to sea, from a positioneast of Vinga lighthouse. Top: The in- and outbound seaways and the NoGo area polygons areset to show depths less than 10 meters. Bottom: the sea surface is removed, showing the tradi-tional chart texture used to drape over the bottom topography. The resolution of the bathyme-trical data is in this case no better than in the normal chart. The intention is to have high re-solution data.

Fig. 7. The experimentarea: 6 m by 6 m squaremarked on a studio floor.Some boxes, a paper tubeand a chair were used asnavigational aids. Thechart is displayed on a lap-top screen (see Figure 8).




The Paper Map. A traditional paper map,similar to map A in Figure 8 but without thegreen arrow. The subjects held the map intheir hand while they drove the cart throughthe track. They were allowed to orient themap as they whished.

The North-up Map. The map was dis-played on the laptop screen and functionedas an electronic chart in north-up mode (seeMap A in Figure 8). The map was static onthe screen and the green arrow moving overthe display showed the position and the ori-entation of the cart.

The Head-up Map. The map was displayedon the laptop screen. In this case the smallgreen arrow was static in the centre of thelower portion of the screen (see Map B in Fig-ure 8). Instead the map moved and rotatedas an electronic chart in head-up mode.

The 3D Map. A simple 3D model of the «ar-chipelago» was made and displayed on thelaptop screen (see Map C in Figure 8). The po-sition of the cart was marked by a green poleand the virtual camera viewed the scene froman over-the-shoulder egocentric position.

The ExperimentThe test subjects were forty five volunteers:available students, staff from the universityand their family members 21 were femaleand 24 male and age ranged from 16 to 63.

Each subject drove the cart four timesthrough four different track designs. Onenew track for each map type. The length andthe number of turns in each track was aboutthe same. The order of the different track de-signs was always the same. The order of thefour map types was randomized, so that onesubject would start with the egocentric 3-Ddisplay on track 1 and the next subject mightstart with the paper map on the same track.

The test subjects were instructed that thepurpose was to drive the cart along the track(yellow squares) as fast as possible withoutgroundings (entering into the red areas onthe map). It was explained to the subjectsthat this was not a competition and that the

purpose of the experiment was to test the ef-ficiency of different maps, not the skill of theparticipants. They should pick a strategy(from quick and sloppy to slow and careful)that they felt comfortable with and try tokeep to that same strategy throughout theexperiment. Then they were guided througha practice session. When the subject feltready, the experiment started.

The time on track and the number ofgroundings were automatically logged by thesystem during the experiment sessions

After the sessions the subjects were inter-viewed briefly about their previous naviga-tion experience and they were asked to fill ina ranking form where they ranked the fourmap types according to user friendliness.They also took a standard spatial ability test.

ResultsThe results (left side of Figure 9) showed

Fig. 8. Three of the four map types used in the experiment. Here they show the position the cartin Figure 7. A is the north-up map (static map, moving arrow), B is the head-up map (staticarrow, moving map) and C is the 3D map (static green pole, moving environment). The fourthmap was a paper printout of map A (without the green arrow).


Thomas Porathe


that the 3D chart was «fastest» with a meantime-on-track for all 45 participants of 111seconds. The head-up chart came in secondwith a mean of 142 seconds followed bynorth-up map with 167 seconds and the pa-per chart with 230 seconds. In this test, deci-sion making was 28% slower using a head-upmap compared to a 3D map and 50% slowerusing a north-up map.. Decision making us-ing a traditional paper map was over 100 %slower than with the 3D map.

The mean number of «groundings» fol-lowed the same trend. Use of the 3D map re-sulted in the lowest number of groundings, amean of 1.7 groundings for the whole group.The mean number of errors was 3.6 using thehead-up map, 4.2 using the north-up mapand 8.2 using the paper map. Compared tonavigation with a 3D map, wayfinding with ahead-up map gave more than twice as manygroundings. A north-up map gave one and ahalf times more groundings and the papermap resulted in almost five times as manygroundings as the 3D map.

The difference in time on track was statis-tically significant at the 1% level for the fourmap types (F(3,132,0.01) = 46.6, p < 0.01). Theinfluence of the map type on the number ofgroundings was also statistically significantat the 1 % level (F(3,129,0.01) = 3.94, p < 0.01).

The subjects were asked to rank the userfriendliness of the different map types from1-4, where «1» was the easiest and «4» themost difficult map to use. The 3D map was

classified as the easiest with a mean index of1.13 followed by the head-up map with amean index of 2.29. North-up was rated 3.24and the paper map 3.33. The paper and thenorth-up maps were considered almostequally difficult to use.

For a more thorough presentation of thisexperiment and how age, sex, navigationalexperience and spatial ability influenced theresults, see [5].

Discussion

The Egocentric View

Navy and high speed passenger ferries com-monly navigate at speeds of about 40 knotstoday. There have been several accidents inScandinavia where the bridge officers havelost their orientation and not been able to re-gain it quickly enough. Speeds at sea contin-ue to increase. Examples are the so-calledRIB boats used for tourist excursions and thenew Norwegian fast patrol boats in Skjoldclass that can have a speed of 60 knots. But itis still the same human brain behind thewheel.

There is less time for decision making andthere is more information to consider in ourever more effective information systems. Weneed to think of ways to display the right in-formation at the right time and in a way thatis unambiguous and easy to understand.

Fig. 9. The left diagram shows the mean time on the track for all subjects and the four map ty-pes. The right diagram shows the mean number of «groundings» made by the subjects for thefour map types.




One could say that there was a point to thehodological perspective of the ancient Ro-mans and the step by step navigation of theitineraries which hid unnecessary informa-tion and just gave what was needed to reachthe next stop.

A transfer of this concept to a modern nau-tical perspective and the conning situationmight be to present the navigator with anegocentric map with high resolution in theforeground and a low resolution overview inthe background, a track to go and the dan-gers in the vicinity. This is what is offered bythe egocentric view, the seaways and theNoGo area warnings.

The laboratory experiment describedabove showed the efficiency of egocentricconning. Planned sea tests during 2007 willshow if this also applies in real life situa-tions.

A Nautical GISOf course an ideal nautical chart should con-tain all the geographical information rele-vant to the mariner. Today the mariner hasto search several different sources to gathernecessary route information (e.g. pilot books,lists of light and fog signals, tide tables).

The 3D nautical chart prototype consistsof both a digital, «flat» map and a so- called

2.5-D terrain skin draped with orthophotoand map texture. The ultimate goal of thisproject is to suggest a Nautical GIS where allinformation relevant to the mariner could bestored and easily updated without having toregenerate the whole terrain skin. An idealGIS might consist of a true 3D database stor-ing currents, temperatures and salinity ofthe sea in volume voxels allowing for time-based simulation of tidal currents, for in-stance. Such a database structure wouldneed huge amounts of data storage space andprocessing power, however, and we will notbe there for a long time. But we will eventu-ally.

It should be possible to update the bathy-metrical database with areas of high resolu-tion as these data become available, so thedatabase resolution needs to be dynamic.

In cartography the concept of map gener-alisation has improved the legibility of maps.They are not just an air photo, they displaythe information which is relevant for the tar-get group. In the same way, the photorealis-tic rendering of the present egocentric viewwill need further research to attain a higherlevel of generalisation and improve legibility.Cartoon rendering techniques offer interest-ing possibilities here (see Figure 10). Thiswill be one area of future research.

ConclusionsThis paper has summarized an ongoing re-search project at Mälardalen University inSweden. In the coming year the chart will beevaluated and tested at sea and its possible

consequences in practical navigation will bepredicted, in cooperation with the MaritimeAcademy at Chalmers University of Technol-ogy.

Fig. 10. Here is an example of so-called «cartoon rendering» techniques applied to Vinga light-house in the 3D chart. Future research will show if this is a way to improve the legibility of ego-centric view maps.


Thomas Porathe


The chart addresses human factors issuesin the maritime domain and attempts to ad-dress some of the problems of informationoverload by removing the need for cognitive-ly demanding tasks and presenting informa-tion in a way more adapted to the humanbrain.

The experimental results presented in thispaper are promising and followup studiesare planned to further test the proposedchart’s applicability.

References1. Antonine Itinerary, http://www.roman-brit-

ain.org/geography/itinerary.htm2. Brodersen, K. Terra cognita Studien zur

römischen Raumerfassung. Olms, Hildershe-im. 1995.

3. Cotter, C. Coastal Views in the Developmentof the Nautical Chart. London: The Hydro-

graphic Society. The Hydorgraphic JournalNo. 17, 1979

4. Janni, P. La mappa e il peripolo. Cartografiaantica e spazio odologico. In Bretschneider, G.(Ed. ) Pubblicazioni della Facoltà di lettere efilosofia - Università degli studi di Macerata.ISBN : 88-85007-79-1. 1984

5. Porathe, T. 3-D Nautical Charts and SafeNavigation. Maladalen University Press,2006. Retrieved April, 2007 fromhttp://www.diva-portal.org/index.xsql?lang=enSearch for author «Porathe.»

6. Shepard, R. N., & Metzler, J. Mental rotationof three-dimensional objects. In Science, 171,1971. pp. 701-703.

7. Taylor, E. G. R. The Haven-Finding Art. Lon-don: The Institute of Navigation, Hollins &Carter, 1956.

8. Whittacer, C.R. Rome and Its Frontiers: TheDynamics of Empire. Routledge, N.Y. 2004


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