Google Earth displays satellite images of varying resolution of the Earth's surface, allowing users to see things like cities and houses looking perpendicularly down or at an oblique angle (see also bird's eye view). The degree of resolution available is based somewhat on the points of interest and popularity, but most land (except for some islands) is covered in at least 15 meters of resolution.
Google Earth allows users to search for addresses for some countries, enter coordinates, or simply use the mouse to browse to a location. For large parts of the surface of the Earth only 2D images are available, from almost vertical photography. Viewing this from an oblique angle, there is perspective in the sense that objects which are horizontally far away are seen smaller, like viewing a large photograph, not quite like a 3D view.
3D images of terrain and buildings are available for other parts of the Earth's surface. Google Earth uses digital elevation model (DEM) data collected by NASA's Shuttle Radar Topography Mission (SRTM). This means one can view the whole earth in three dimensions.
Google Earth is simply based on 3D maps, it has the capability to show 3D buildings and structures (such as bridges), which consist of users' submissions using SketchUp, a 3D modeling program software. Many buildings and structures from around the world now have detailed 3D structures.
NASA World Wind
World Wind is a free and open source (released under the NOSA license) virtual globe developed by NASA and the open source community for use on personal computers. Old versions need Microsoft Windows but more recent Java versions are cross platform. The program overlays NASA and USGS satellite imagery, aerial photography, topographic maps and publicly available GIS data on 3D models of the Earth and other planets.
World Wind was released for the first time in 2004 by NASA. The latest version (1.4) developed mainly by open source community members from World Wind Central/Free Earth Foundation had its premiere on February 14, 2007.
Apart from the Earth, there are several worlds in World Wind: Moon, Mars, Venus, Jupiter (with the four Galilean moons of Io, Ganymede, Europa and Callisto) and SDSS (imagery of stars and galactics). All these worlds are available in the File menu.
Users can interact with the selected planet by rotating it, tilting the view, and zooming in and out. Five million placenames, political boundaries, latitude/longitude lines, and other location criteria can be displayed. World Wind provides the ability to browse maps and geospatial data on the internet using the OGC's WMS servers (version 1.4 also uses WFS for downloading placenames), import ESRI shapefiles and kml/kmz files. This is an example of how World Wind allows anyone to deliver their data.
Other features of World Wind include support for .X (DirectX 3D polygon mesh) models and advanced visual effects such as atmospheric scattering or sun shading.
The resolution inside the US is high enough to clearly discern individual buildings, houses, cars (USGS Digital Ortho layer) and even the shadows of people (metropolitan areas in USGS Urban Ortho layer). The resolution outside the US is at least 15 meters per pixel.
Microsoft has allowed World Wind to incorporate Virtual Earth high resolution data for non-commercial use.
World Wind uses digital elevation model (DEM) data collected by NASA's Shuttle Radar Topography Mission. This means one can view topographic features such as the Grand Canyon or Mount Everest in three dimensions. In addition, WW has bathymetry data which allows users to see ocean features, such as trenches and ridges, in 3D.
Many people using the applications are adding their own data and making them available through various sources, such as the World Wind Central.
All images and movies created with World Wind using Blue Marble, Landsat, or USGS public domain data can be freely modified, re-distributed, and used on web sites, even for commercial purposes.
Virtual Terrain Project
The goal of VTP is to foster the creation of tools for easily constructing any part of the real world in interactive, 3D digital form.
This goal will require a synergetic convergence of the fields of CAD, GIS, visual simulation, surveying and remote sensing. VTP gathers information and tracks progress in areas such as procedural scene construction, feature extraction, and rendering algorithms. VTP writes and supports a set of software tools, including an interactive runtime environment (VTP Enviro). The tools and their source code are freely shared to help accelerate the adoption and development of the necessary technologies.