There are several free data sources available with geodata that can be used by the Silent Wings scenery tools. To make a scenery you basically need two kinds of data, elevation data and texture data. Elevation data are usually raster images with elevation values instead of colors, and texture data should be georeferenced images such as satellite or arial photos.
The main source for elevation data these days is the Global SRTM data set. This data set covers the earth between 60 degrees north and 60 degrees south with approximately 90m resolution, i.e 90m grid cells in the raster. The SRTM data set itself has a few problems, such as holes and uneven water surfaces. Therefore we recommend using the CGIAR data set instead which is a brushed-up version of the SRTM data.
Jonathan de Ferranti has done an amazing job of manually processing and enhancing various kinds of elevation data to produce DEM files with up to 20m resolution. These files are primarily avaialble for mountainous regions, and can be downloaded here
The SRTM data set does not cover areas far to the north or south (above or below +/- 60 degrees latitude). In these areas, the best free elevation data source is the global SRTM30 data set. This data set is 1km resolution only and is based on the older GTOPO30 global data set.
For the United states you can get high resolution (10 or 30m) elevation data for the continental US. They can be downloaded either in NED format from the seamless data server, or as DEM files from various sources (see ). We support both the old .DEM format and the newer SRTM format. SRTM files can be used directly as tar archives, no need to untar them first.
Good satellite images and aerial photos are very hard to come by, at least for free. The best global freely available data sets are based on Landsat 7 satellite images which are 28m/pixel, but can be sharpened up to 14m/pixel. This is what we use for the Europe scenery for instance. NASA has a version of these data called NASA OnEarth. This data set is available in several different versions, but the best is the natural color composite in 14m/pixel. The colors are not perfect, however, and there are some clouds in these images. In addition, the images are delivered in JPEG format and contain some compression artifacts.
The best solution for Landsat7 data is to download the raw data and process them yourself. One good source for Landsat data is GLCF which has global coverage of Landsat 7 and Landsat 5 data + a few other daa sets. The processing of these images is quite a big job, and a separate topic in itself. See Paul's excellent [http:// tutorial] on the subject.