Virtual globe |
A virtual globe is a 3D computer graphics computer software model of the earth. Depending on its technology, a virtual globe may be as simple as an inexpensive globe sitting in a typical school class room, or as sophisticated as an integrated interface that provides intuitive access to multiple geographic information system Databases.
= Types =
Most earlier computerized world atlases were not detailed or only had limited area coverages. Today s virtual globes are connected to satellite image servers. These virtual globes are capable of rotation and zooming with many having worldwide coverage.
== Offline virtual globes ==
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.
== Online virtual globes ==
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:
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, [http://www.worldwindcentral.com/wiki/World_Wind_Central_Add-on_Pack here].
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 1km [http://earthobservatory.nasa.gov/Newsroom/BlueMarble/ 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 [http://en.wikipedia.org/wiki/Aqua_(satellite) Aqua] and [http://en.wikipedia.org/wiki/Terra_(satellite) Terra] satellites. An [http://forum.worldwind.arc.nasa.gov/index.phpshowtopic=1932 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.
== Literary References ==
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.
= Features =
Some of today s virtual globes can support these features.
= Comparisons =
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.
[http://www.neave.com/lab/flash_earth/ Flash Earth] is a Macromedia_Flash website that allows you to quickly search and toggle between Google Maps, Virtual Earth, and Virtual Earth with labels.
= External links =
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