Buchroithner, Manfred 
Texture gradient is a quantum for the variation of the texture density depending on the distance. The cue is 
stronger with increasing homogeneity of texture structure. Due to the compression (depending on distance), a 
homogenous texture contribute the depth perception with larger amount as inhomogenous textures. i 
More detailed and exhaustive descriptions and image examples concerning depth cues can be found e.g. in 
Vlahos 1965, Okoshi 1976, Kraak 1988, Albertz 1998, Sieber 1996. 
S GRAPHIC SEMIOLOGY 
For the map production, respectively the cartographic communication process, an encoding of geoinformation in 
graphical, acoustic or tactile information is essential. The publication of the graphique semiologie by Jaques 
Bertin (Bertin 1974) was a initial impulse for wider research in map semiotics. Since that time the system of 
Bertin has been tried to be expanded trough umpteen scientists and adapted for new technologies (e.g. Spiess 
1978, Freitag 1980 & 1996, MacEachren 1995, Dransch 1995, Böhm 1998). 
W.G.Koch (Koch 2000) proposed a system of variables for multimedial cartography based on an extensive 
review of literature. Especially the graphical variables have to be taken into account for 3D hardcopy. Koch 
distinguished in 2D static, 2D dynamic and 3D dynamic graphical variables. The in Koch (Koch 2000) 
mentioned seven static variables are the basis for 2D and 3D dynamic variables in a hierarchical system and 
described as basic variables. Due to the existing strong interaction between the depth cues and the 2D and 3D 
dynamic variables mentioned in Koch (Koch 2000), for sytematisation of 3D hardcopy technologies these 
variables should be considered carefully. 
Kraak (Kraak 1988) proposed a linked system of static variables and depth cues which is useful if the 3rd. 
dimension is considered as thematic dimension. Assuming the third dimension with the same priority than the 
first and second. dimension (e.g. topographic mapping), the depth cues are needed for the localisation of map 
information in 3D space or for the spatial structuring. Thematic information located in map space can be 
encoded in conventional manner by means of static variables. 
With respect to the visualisation technology, static variables are (more or less) used for artifical depth 
perception. The idle variables are available for encoding thematic information: geo object quantity and/or 
quality. Each of them define a degree of freedom for the 3d-visualisation technology for cartographic purposes. 
The degrees of freedom considered for a theoretical comparison of 3D hardcopy with 2D hardcopy (conventional 
map) are size, brightness, colour, pattern, orientation and shape (Bertin 1974). In Buziek (Buziek 1995) the 
potential use of these variables for the visualisation of geoobjects in 3D space is described. 
A systematisation of 3D visualisation technologies can be carried out by rating the visualised image concerning 
the spatial perception and cognition comfort as well as thematic content. The spatial image is defined as an 
artifical phenomenon which is spatially observed by the visual perception system; without the physical existence 
of a real viewing model or scene. 
A spatial image can be termed as optimal perceptive, if the visual perception system is Working in the same way 
as viewing a real scene. From the number and type of included depth cues a degree of perception can be 
estimated. This describes in a broader sense the "nativeness" of the spatial image. 
Beside the degrees of freedom and the degree of perception, the quality of the spatial image regarding natural 
viewing has to be considered. Especially the potential resolution and color depth are parameters which are 
dependent on the display technology. Quality parameters are summarised by the term degree of immersion. 
Thereby the amount for spontaneous cognition of thematic content and the authenticity is described. The highest 
of immersion implies the necessity of additional senses to distinguish between spatial image and reality. 
The focus on the above mentioned three parameters of the theoretical spatial image for each technology allows 
initial assessment for the usability in cartography. 
6 THE 3D DISPLAY TECHNIQUES 
Buziek (Buziek 1995) points out that the term visualisation is used with different meanings. Therefore it should 
be noted that in the frame of this paper visualisation is used in the sense of the representation ofa spatial image. 
Consequently it has to be distinguished between the visualisation device (e.g. paper) and the visualised image 
(spatial image). Likewise flat images, spatial images can be represented by softcopy and hardcopy devices. 
Softcopy can be summarised as technologies with the necessity of electronical, computer-driven device, which 
are in general self-illuminating. 
Hardcopy use non electronical display devices without the capability of self-illumination. They influence leight 
fields in different ways to produce the spatial image. 
On the basis of the degree of perception of the visualisation technologies the classification into the following 
major groups is proposed. 
  
  
102 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B5. Amsterdam 2000. 
  
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