Home Planet for Windows

Release 3.2 Earth Image Upgrade

Release 3.2 of Home Planet for Windows is an incremental update to release 3.1 which adds a natural colour Earth image database for use in the Map and View From displays. The new Earth images are based on the cloudless Earth databases created by the NASA Goddard Space Flight Center from the MODIS instrument onboard the Terra satellite.

The original NASA imagery has been specially processed for use in Home Planet and incorporated into a MAPBITS.DLL file which replaces the corresponding file in the Home Planet 3.1 release archive. If you already have Home Planet 3.1 installed on your machine, you need only download the new Earth image database and install it in your Home Planet directory. If you're new to Home Planet, download the 3.1 release from the main Home Planet page, and after you've installed and tested it, download and install the 3.2 update described here. Home Planet 3.2 is provided only as an upgrade to 3.1 to reduce download time for the many existing users of 3.1. A new full release of Home Planet including this database and additional features will be posted in the near future.

The new Earth image database is available in two different editions. The high resolution edition includes a cloudless Earth image with 81924096 pixel resolution--more than 32 million pixels. This image provides superb resolution when a large map window is displayed on a high resolution screen and in views from satellites at low altitude. Compare, for example, the view at the right of the British Isles from an altitude of 600 km with that produced from the databases supplied with Home Planet 3.1.

Such high resolution comes, of course, at a cost. The archive containing the image is a 7.6 Mb download, and extracts to a 37 Mb DLL file; to install and use it you'll need sufficient free disc space, RAM in excess of 64 Mb, and a processor fast enough to render such a large image in an acceptable time. Machines with more modest configurations should install the medium resolution edition. Its cloudless Earth database is 20481024 pixels, yielding a 1.26 Mb download and 3.4 Mb extracted DLL file. The high resolution edition includes the lower resolution cloudless Earth image as an option, and both editions include both the large and small NOAA topographic maps supplied with Home Planet 3.1. The "Gaudy map" included with 3.1 is obsoleted by the NASA imagery and is no longer included.

Downloading and Installation

To install the new Earth image database, first download the edition you prefer from one of the following links. The archives are supplied in Zipped form--extract the contents with Info-ZIP or an equivalent utility to obtain a README.txt file with additional installation information and the new MAPBITS.DLL containing the Earth image databases.

To install the new Earth image database, first make sure Home Planet is not running--if it is, quit the program. Then simply copy the MAPBITS.DLL you extracted from the archive into the directory into which you installed Home Planet, overwriting the MAPBITS.DLL already there. To be extra careful, you might want to first copy the existing MAPBITS.DLL to a file named, say, MAPBITS.OLD so you can easily restore it if you encounter difficulties with the updated database.

Once MAPBITS.DLL is copied into the Home Planet directory, launch Home Planet and use the Display/Map image menu item to choose whichever image you prefer. The large NASA image in the high resolution edition provides the highest resolution and drastically improves the quality of views from satellites in low Earth orbit.

Large Image Clipboard Problems on Windows 95/98/Me

There appears to be a bug in some mass market versions of Windows based on the 16 bit legacy code which results in errors when the 81924096 pixel NASA image in the high resolution edition is selected and you attempt to copy the Map window to the clipboard with the Edit/Copy menu item. The copy operation appears to complete normally, but the image on the clipboard is gibberish. This problem does not occur on Windows 2000, so I suspect it is a Windows 9x/Me bug related to very large images. If you encounter this problem and need to copy the Map window to the clipboard, select the small NASA image before performing the copy--that seems to work without problems on all versions of Windows. The screen capture facility of most paint programs also seems to work with the high resolution map--this can provide an alternative to copying the map image to the clipboard.

Note to Developers

If you're a developer interested in obtaining a cloudless Earth image for use in your own application, you're much better off starting with the original NASA images.

While you're perfectly welcome to extract the BMP images embedded in MAPBITS.DLL, note that in order to work efficiently with Home Planet the 24 bit per pixel true colour NASA images have been compressed into a palette of just 117 day and 117 night colours, resulting in loss of subtle detail. In Home Planet's use of the images, the difference is rarely perceptible, but for more demanding high-resolution applications the true colour originals will provide superior quality.

Home Planet for Windows

Fourmilab Home Page


by John Walker
August 18th, 2002