Virtual globe
From Wikipedia, the free encyclopedia
A virtual globe is a 3D software model or representation of the Earth or another world. A virtual globe provides the user with the ability to freely move around in the virtual environment by changing the viewing angle and position. Compared to a conventional globe, virtual globes have the additional capability of representing many different views on the surface of the earth. These views may be of geographical features, man-made features such as roads and buildings or abstract representations of demographic quantities such as population.
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[edit] Types
Virtual globes may be used for study or navigation (by connecting to a GPS device) and their design varies considerably according to their purpose. Those wishing to portray a visually accurate representation of the Earth often use satellite image servers and are capable not only of rotation but also zooming and sometimes horizon tilting. Very often such virtual globes aim to provide as true a representation of the world as is possible with worldwide coverage up to a very detailed level. When this is the case the interface often has the option of providing simplified graphical overlays to highlight man-made features since these are not necessarily obvious from a photographic ariel view. The other issue raised by such detail available is that of security with some governments having raised concerns about the ease of access to detailed views of sensitive locations such as airports and military bases.
Another type of virtual globe exists whose aim is not the accurate representation of the planet but instead a simplified graphical depiction. Most early computerized atlases were of this type and, while displaying less detail, these simplified interfaces are still widespread since they are faster to use because of the reduced graphics content and the speed with which the user can understand the display.
[edit] Online virtual globes
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As more and more high-resolution satellite imagery and aerial photography become accessible for free, many of the latest online virtual globes are built to fetch and display these images. They include:
- Norkart Virtual Globe, first version released summer 2001 as the SINTEF Virtual Globe.
- NASA World Wind, USGS topographic maps and several satellite and aerial image datasets
- Google Earth, based on the Google Maps international street-level dataset and several satellite and aerial datasets (including private Keyhole images)
- Earthsim, from Servan Keondjian which displays real-time 3D rendered views and information about the Earth.
As well as the availability of satellite imagery, online public domain factual databases such as the CIA world factbook have been incorporated into virtual globes.
[edit] Technical info, data and image sources
Although by default the World Wind download only comes with public domain imagery from the USGS and Landsat 7, Community members have made available high resolution imagery for New Zealand and New York, here and additional countries.
Google Earth, NASA World Wind and Norkart Virtual Globe save a cache of downloaded imagery to the user's hard disk, enabling them to be used offline to view previously viewed areas. However, you cannot activate Google Earth without logging into its server for the first time.
The Google Earth's cache size is limited to 2000 MB whereas World Wind has no limit on cache size. In Norkat Virtual Globe the disk cache can be set by the user.
In addition to downloaded images, NASA World Wind also comes with the complete 500 m Blue Marble imagery and global placenames including countries, capitals, counties, cities, towns and historical references which are available from install.
World Wind is also capable of displaying MODIS imagery from the JPL Aqua and Terra satellites. An Add-on allows for near-real-time MODIS imagery.
Google Earth and Virtual Earth are both capable of displaying many more urban areas in high-resolution thanks to their private image sources. Both companies also hire chartered flights over major cities of the U.S. to take aerial images.
[edit] History
The use of virtual globe software was widely popularized by (and may have been first described in) Neal Stephenson's famous science fiction novel Snow Crash. In the metaverse in Snow Crash there is a piece of software called Earth (just like Google's), made by the Central Intelligence Corporation. The CIC uses their virtual globe as a user interface for keeping track of all their geospatial data, including maps, architectural plans, weather data, and data from real-time satellite surveillance.
Virtual globes (along with all hypermedia and virtual reality software) are distant descendants of the Aspen Movie Map project, which pioneered the concept of using computers to simulate distant physical environments (though the Movie Map's scope was limited to the city of Aspen, Colorado).
[edit] Features
Some of today's virtual globes can support these features.
- Multiple datasets (World Wind, Norkart)
- Street map overlay (Google Earth, Norkart, Virtual Earth 3D)
- Restaurant, hotel, transportation ... guides (Google Earth)
- Satellite and aerial image overlay (Google Earth, World Wind, Norkart, Virtual Earth 3D)
- Weather map overlay (Google Earth, World Wind)
- Real-time traffic report
- GPS-integration (Google Earth, World Wind - see here)
- 3D graphics (Google Earth, World Wind, Norkart, Virtual Earth)
- 3D building models (Google Earth, Norkart, Virtual Earth 3D)
- Terrain models (Google Earth, World Wind, Norkart Virtual Globe, Virtual Earth 3D)
- Sea-floor models (World Wind, Norkart Virtual Globe)
- Planetarium (Google Earth)
- Day/night views (World Wind)
- Views of other planets (World Wind, Norkart Virtual Globe (Mars))
- Online community user input (Google Earth, World Wind)
- Wikipedia integration (Google Earth, World Wind)
[edit] See also
[edit] External links
- 3D VRML globe
- Earthsim - virtual globe from one of the pioneers of Direct3D, Servan Keondjian
- EarthSLOT - online 3D globe - University of Alaska Fairbanks project
- Google Earth - Google Earth's official site
- GRIFINOR - Decentralized Platform for GeoVizualization
- NASA World Wind - official project website at NASA.
- Norkart Virtual Globe (Java- and JOGL-based, start directly here).
- TerrainView - by ViewTec
- Virtual Globes Directory - links to virtual globes
- Virtual Mapping - Metastream planet globes by Craig Dunning 1999
- World Wind Central - Community-run website concerning NASA World Wind
