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- What are the hardware
requirements for the program?
The program uses OpenGL and QT to view the earth. It downloads the texture and heightfield data on demand over the internet. You need at least DSL speed (about 768kbit) to use it. I tested it on an Athlon 850Mhz with an Nvidia Geforce 2 MX.
- Where does the texture and
heightfield data come from?
The data is downloaded transparently from a webserver containing about 1.5 GB of data. The data itself belongs to NASA, USGS and the city of Osnabrück.
- Can I download the full
dataset?
The full dataset is currently available from here (http). The file is a 1.1 GB ZIP file. You can download and use it to run the program on computers that do not have the needed bandwith for loading the data over the internet. To use it, extract it somewhere. Then start earth3d and click on the magnifying glass icon in the top left corner of the window. Choose "URL" and click "Browse files". Choose the file earth/service.sxml from the extracted files and click OK. The five earth maps should appear in the tree view on the left.
Note: Several people downloaded this file and used programs to unzip it, that could not handle so many files in an archive. You can use the free zip program called 7-ZIP. I tested to extract the archive using version 3.13 and it worked without any problems! (Whereas the preview function of Windows XP was wrong, it thought there would be about 11000 files in the archive, which is wrong.)
Here are some additional hints:
The service.sxml file is in the earth subdirectory:
4092 12-03-04 03:33 earth/service.sxml
The archive contains 1195321199 bytes in 329120 files and has a md5sum of
$ md5sum earthdata.zip
7b571b545bc40e27a6e2423a887ffd9d earthdata.zip
The archive itself has a size of 1131885515 bytes.
- I get a message
complaining "/usr/lib/libGL.so.1: no version information available"
or The program stops after printing "CONNECTTOSERVER"
In both cases you have to check your graphics card driver and your OpenGL driver. Frequently people used an ATI graphics card, but did not use the drivers from www.ati.com. So please try to install ATI's graphics card driver if you have an ATI graphics card.
- How is the server data organized? First there is a service.sxml file that describes which maps are available. It contains information about the icons for each map and the location of a geometry.mxml file. The geometry.mxml file contains links to the root node of the heightfield and the texture tree. Every node in these two trees contains some data about the node itself and links to the four subtiles. These trees describe a quadtree. That means the tree starts with a map with a size of 256x256 pixels containing the whole earth. This map is divided into four quarters and every quarter is saved with a size of 256x256 pixels under the parent node (each containing another quarter of the original map). So with every layer of the tree the resolution of the map is doubled.
- Where can I get the
server software?
The server software is available via sourceforge's CVS. It is a simple command line tool that was tested under Linux. A new (release 29.11.2005) binary windows version can be downloaded here: earth3d_server_windows_1.zip.
It can be used to add maps to a global map. E.g. when you look at the "MODIS Satellite map earth" there are several smaller maps with higher detail embedded into the global map, e.g. in Europe, Florida and Japan. In these areas the quadtree is deeper to server the higher resolution images. The command line tool can easily used to integrate these maps by just specifying the map file (must be .tif or .png) and the coordinates where it should be embedded (coordinates range from 0 to 1 in double format so when you know the GPS coordinates of the corners you can easily convert it). You should be aware that the projection of the map format must be "Plate Carree" or a similar grid aligned format.
You can find further documentation of the usage on the "documentation" pages on www.earth3d.org and inside the windows binary ZIP file.
Every node in the tree contains a small map 256x256 pixels in size and four links to other nodes.
The links are normally URLs that can be relative or absolute. This makes it possible to save parts of each map (e.g. a single country or continent) on another server than the rest of the map.
The heightfield map tiles are saved in PNG format, the texture map tiles in JPG format.
To save XML data and binary data in all these files (service.sxml, geometry.mxml and in the tree nodes) a simple file format was invented:
<number of blocks>LF
<size of block 0>LF
<data of block 0>
<size of block 1>LF
<data of block 1>
...
Block 0 contains the XML file. The number and size fields are simple ASCII-Numbers followed by a linefeed (10) character.