These images are updated at most every three hours. If you are using a script or otherwise automate your download, do not run it more often than that.
The preferred site to download the most recent cloud image is http://xplanet.sourceforge.net/clouds/clouds_2048.jpg. There is also a 4096x2048 pixel cloud image at http://xplanet.sourceforge.net/clouds/clouds_4096.jpg. This address uses the Coral content distribution network and will automatically download the cloud image from a Coral server near you. You may also use one of the mirror sites from the list below.
- Australia
- France
- Germany
- Korea
- The Netherlands
- United Kingdom
- United States
Oliver White at cueSim has written a perl script to download the cloud map from a random mirror, and checks if the current image is less than three hours old before connecting. Michal Pasternak has written a similar script in Python. Please use one of them!
The cloud map creation time is embedded as a JPEG comment in the file. These images are not real snapshots nor are they particularly accurate; they are mosaics created from geostationary weather satellite images. The times of the source images may differ by several hours since they are only available at limited times during the day. The cloud maps are not calibrated or carefully geolocated. They are only meant to make the earth look pretty!
You can also use cloud maps from the Space Science and Engineering Center at the University of Wisconsin. Their Global Satellite Composites are updated every three hours. Use the cloud_ssec option in the configuration file for versions later than 1.0, or the -cloud_ssec option for versions before 1.0.
Why isn't there a permanent link to the latest image?
Previously, you could download the cloud map directly from the main xplanet web page. I was told by Sourceforge that the cloud map was getting upwards of 300,000 hits per day. At 400 KB per download, that translates to 120 GB every day. Most of that was due to people irresponsibly using automated downloads to get the cloud map. There were people downloading the same image every second. Providing a cloud map is outside of Sourceforge's focus on open software development anyway, so now the cloud maps are distributed using Coral and the mirror sites listed above.
Please don't ask me to send you the code I use to generate the cloud maps. That would just shift the traffic to the University of Dundee servers, and that would be a bad thing.