
    	    	    	Home Planet for Windows
		    Release 3.2 Earth Image Upgrade
		       Medium Resolution Edition
		    
		       Installation Instructions
		            by John Walker
		        http://www.fourmilab.ch/
		           August 18th, 2002
		       
     -----------------------------------------------------------
	
This archive contains a MAPBITS.DLL file which upgrades the
Earth image databases supplied with Home Planet 3.1 to include
a medium resolution (2048×1024 pixel) natural colour cloudless
Earth image prepared by the NASA Goddard Space Flight Center
based on imagery collected by the MODIS instrument on the Terra
satellite.  For details on this and other Earth image
databases, please visit the NASA Earth Observatory site:

    http://earthobservatory.nasa.gov/
    
The original NASA image has been adapted for use with Home
Planet by compressing its colour gamut and including a palette
to represent the night side of the planet in subdued colours.
The enclosed MAPBITS.DLL supplies three different Earth map
images:

    1.  The 2048×1024 NASA cloudless Earth image.
    2.  The NOAA-MGG Earth topographic map at full (1440×720)
        resolution.
    3.  The NOAA-MGG Earth topographic map at half (720×360)
        resolution.
	
The latter two images were included in the MAPBITS.DLL supplied
with Home Planet releases 3.1 and earlier; the "Gaudy map" included
with those releases has been rendered obsolete by the NASA imagery
and is no longer included.

Installing the New Image Database
---------------------------------

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 this 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.

Higher Resolution Earth Images
------------------------------

A cloudless Earth image with sixteen times the resolution
(8192×4096 pixels) is available in a Home Planet map database
which may be downloaded from:

    http://www.fourmilab.ch/homeplanet/download/3.2u/mapbits-32u.zip
    
The MAPBITS.DLL in that archive includes the three images
described above, plus the high resolution natural colour
cloudless Earth imagery.  The high resolution map is more than
32 megabytes in size and requires free disc and RAM space of
that magnitude and a fast processor to install and use
effectively.  The difference between the medium and high
resolution Earth images is most apparent in views from
satellites at low altitudes.

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 available from:

    http://earthobservatory.nasa.gov/Newsroom/BlueMarble/
    
While you're perfectly welcome to extract the BMP images
embedded in this 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.
