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 WorldWind to incorporate Virtual Earth high resolution data for non-commercial use. WorldWind uses digital elevation model (DEM) data collected by NASA's Shuttle Radar Topography Mission (SRTM), National Elevation Dataset (NED) and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). 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 are making them available through various sources, such as the WorldWind Central or blogs mentioned in the link section below. All images and movies created with WorldWind using Blue Marble, Landsat, or USGS public domain data can be freely modified, re-distributed, and used on web sites, even for commercial purposes. Add-ons and plugins WorldWind can be expanded by using one of many add-ons - small extensions that add new functionality to the program. Possible types of add-ons: Point layers: simple XML files displaying placemarks (point of interest) as icons Trail layers: paths (routes, boundaries) Line features: XML with a list of points visualized as a line or wall Polygon features: XML with a list of points visualized as a filled polygon (flat or extruded) Model features: XML used to load 3D textured meshes Place names: specific points (such as cities, hills and buildings) that are assigned text labels Image layers: high resolution imagery for various places in the world Scripts: files that control camera movement Plugins are small programs written in C#, VB or J# which are loaded and compiled by WorldWind at startup. Plug-in developers can add features to WorldWind without changing the program's source code. WorldWind Java The original recipe for WorldWind was restricted to Windows, relying on the .NET libraries and DirectX. A new SDK version has been developed in Java with JOGL referred to as WorldWind Java. The latest version (2.2.0) was released in August 2020. This new version has an API-centric architecture with functionalities 'off-loaded' to modular components, leaving the API at the core. This makes WorldWind itself a plugin, so that it can be used as interchangeably