GEOG 486
Cartography and Visualization

3-D Visualization

PrintPrint

The problem of representing three-dimensional geographic information is not new to cartographers. In this lesson, we have already discussed some techniques that cartographers commonly use for this task, Isolines and Shaded Relief. In this concept gallery item, we will focus on other techniques for visualizing 3D data.

The software tools and techniques that are available to cartographers for 3D visualization are rapidly changing as new techniques and even new programming languages are developed. For this reason, we will structure our discussion of 3D visualization methods by discussing several attributes that we can use for classifying methods and techniques.

One of the most basic distinctions that we can use is whether the method uses a perspective view of the 3D space, or whether it is an immersive view. In a perspective view, the map reader is outside of the space and looking in at it, while in an immersive view, the map reader feels like s/he is actually within the space. An example of a perspective view can be seen in the rotated TIN and shaded relief images shown earlier in this lesson. This type of perspective view can be easily created with standard GIS software. More immersive views can be created by 'flying' over or through a perspective view (e.g., using GeoVRML, the geographic virtual reality modeling language and an internet connection) or by using specialized virtual reality software that projects images onto screens that physically surround the viewer (e.g., the CAVE virtual reality environment).

A photo to show how augmented reality provides a map reader with a view that can be rotated. visual spaceA screen capture of the CAVE environment.
Figure 6.cg.40 and Figure 6.cg.41 In the example above, at left, augmented reality provides a perspective view that the map reader can rotate (Hedley et al. 2002), but does not provide the true immersive perspective found in the CAVE environment (above right) (Johnston and Reetz 2004).

To get a better simulation of the experience of using the CAVE, Play the movie below. It shows user interactions with the CAVE (Johnston and Reetz 2004).

Movie tracking user movements in the CAVE environment.

A second distinction we can make is between static visualizations and dynamic visualizations. Static visualizations most often take the form of perspective views, and allow the map reader to imagine the three-dimensional configuration of a phenomenon from only one angle or vantage point (see Figure 6.cg.42, below). Dynamic visualizations may involve the map reader's movement through the space (either physically as can occur in the CAVE, or virtually with a fly-by) and may also allow the user to change various display parameters while viewing the representation (e.g., their viewpoint, the attributes being shown, the amount of vertical exaggeration present in the image, etc.). An example of a dynamic visualization can be seen in the David Rumsey Map Collection's 3D GIS view ( http://www.davidrumsey.com/GIS/3d.htm).

A graphic representation to show, in a static perspective view, the location of glaciers at a certain point in time.
Figure 6.cg.42 The example above depicts the location of glaciers at a particular point in time in a static perspective view.
Credit: Samaga, 2002

Some types of 3D visualization only allow one viewer to investigate the visualization at a time. For example, in some virtual reality systems, the images are displayed through a device called a head mounted display, which can only be worn by one person at a time (see Figure 6.cg.42, below). Other applications allow groups of people to see the same thing at the same time and to even hold discussions about the visualization while they are viewing it (e.g., an ImmersaDesk (see Figure 6.cg.43, below)) or a CAVE, which is big enough to hold several people at once).

A man wearing a head mounted display unit.
Figure 6.cg.43 With a typical head mounted display, only one map reader can view a visualization at a time.
Credit: Virtual Realities, 2004
A man using an Immersadesk device.
Figure 6.cg.44 Here, a scientist uses an Immersadesk to explore a 3D representation of temperature data. In this case, the third dimension is used to represent change in the variable over time rather than elevation or altitude. An advantage of the Immersadesk is that several people can view images simultaneously.
Credit: MacEachren et al., 1999

A final important point about three-dimensional visualizations is that the symbolization that cartographers use to create these types of representations can range from very abstract (e.g., geometric figures of objects) to highly realistic (e.g., visualizations of cities with buildings, trees and people rendered realistically). The cartographer's choice of symbolization will often be influenced by the expertise of the map readers who will view the representations and the tasks they will perform or their reasons for viewing the visualization. For example, if a city planner wanted to create a visualization to help inform the public about the potential impact of one design over another on the appearance of an area, the cartographer working with the city planner might choose to use as realistic a depiction of the area as possible. However, a group of scientists studying runoff in a terrain model might be distracted by the realistic rendering of each tree present in the study area, so they might choose to use a more abstract representation of the land cover at a particular site.

A set of screen captures to show a web view of a proposed town center. A screen view of a 2-D plan, along with cost assessment graphs, is paired with a 3-D representation of the site plan.
Figure 6.cg.45 In this example of a spatial decision support system, the 3D visualization is used to show community members how a proposed development would change the landscape.
Credit: Environmental Simulation Center, 2004.

Recommended Readings

If you are interested in investigating this subject further, I recommend the following:

  • Hodges, M. 2000. Seeing data in-depth: 3D GIS gives mainstream users a richer look at their information. Computer Graphics World. 23(5): 43-8.