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Virtual globe

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Google Earth, a highly detailed virtual globe that comes with atmosphere effects, seabed and even a simplified planetarium
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Google Earth, a highly detailed virtual globe that comes with atmosphere effects, seabed and even a simplified planetarium

A virtual globe is a 3D software model or representation of the Earth or another world. A virtual globe may be as simple as an inexpensive globe found in a typical school class room or a sophisticated interface that provides intuitive access to multiple GIS databases. Compared to a conventional globe, virtual globes have the advantage of being able to visually represent 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.

Contents

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.

Offline virtual globes

The full view of a very crude virtual globe.
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The full view of a very crude virtual globe.

Microsoft MapPoint is a detailed recent implementation of virtual globe concepts. Unlike some other computerized local street maps created on a flat land, the MapPoint technology has always been based on three-dimensional geometry. Based on the MapPoint technology, Microsoft published several map programs that include detailed street-level databases of North America and Western Europe for business and home users.

The MapPoint virtual globe is used as an entrance to North American or Western European maps. Outside the street-level database, major cities are only plotted as dots.

The other Microsoft virtual globe is shipped with its offline encyclopedia, Encarta. This virtual globe is also based on the MapPoint technology and contains global placenames and geographical features. Some worldwide major cities contain major street information. However, it does not include any street level databases.

Some virtual globe programs have been used to model plate tectonics. For instance, Time Machine Earth was a late-1980s DOS software that drew crude reconstructed continental outlines for the earth's past.

Three maps generated by MapPoint North America 2001 (outside the detailed dataset), Encarta 2005 (not very detailed) and Microsoft AutoRoute 2004 (highly detailed).
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Three maps generated by MapPoint North America 2001 (outside the detailed dataset), Encarta 2005 (not very detailed) and Microsoft AutoRoute 2004 (highly detailed).


Online virtual globes

NASA World Wind showing the streets of Anchorage, Alaska in 0.25 m resolution.
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NASA World Wind showing the streets of Anchorage, Alaska in 0.25 m resolution.

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:

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. Examples include:

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 SINTEF 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 SINTEF Virtual Globe the disk cache has to be enabled manually.

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.

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).

Features

Some of today's virtual globes can support these features.

Comparisons

This is the Bora Bora you get from NASA World Wind (15 m; Landsat 7 resolution).
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This is the Bora Bora you get from NASA World Wind (15 m; Landsat 7 resolution).

This is the Bora Bora (middle) you get from Google Earth or Google Maps (1 km; "The Blue Marble" resolution).
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This is the Bora Bora (middle) you get from Google Earth or Google Maps (1 km; "The Blue Marble" resolution).

Despite the availability of public domain satellite/aerial imagery datasets, some remote oceanic islands may be ignored. For example, the Bora Bora Island comes in three different resolutions from three sources.

[Flash Earth] is a Flash-based website that allows you to quickly search and toggle between Google Maps, Virtual Earth, and Virtual Earth with labels.

See also

External links

 

From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.

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