Using the Magellan CD-ROMs


The current Magellan CD-ROMs contain the digital image mosaics produced by the spacecraft's synthetic aperture radar instrument during the first 243-day cycle around Venus. Individual disks contain Full-Resolution Mosaic Image Data Records (F-MIDRs), which show the imagery at full resolution, or Compressed (Once or Twice) Mosaic Image Data Records (C1-MIDRs,C2-MIDRs) which cover larger areas at lower resolution. The C-MIDRs cover the entire planet, while the F-MIDRs cover selected areas of probable interest, comprising in total about 15% of the planet.

These disks are the basic archive of Magellan's scientific data for both research and public interest. They have been designed to be usable on all types of computers. The NASA Space Science Data Coordinated Archive (NSSDCA) is the principal distributor of the CD-ROM disks. The NSSDCA CD-ROM Catalog is available on-line which lists all these CD-ROMs. NSSDCA can also provide software to display the images on most computers.

The CDs have been produced in approximately the order in which their imagery was collected by the Magellan spacecraft. However, identifying the precise disk which is needed to view a specific feature or area can be difficult. NSSDCA can also provide a simple Macintosh or PC software called the Magellan Venus Atlas, which tells the latitude and longitude of any named feature on Venus, and then shows the specific CD-ROMs and mosaic images which cover that area.

The images are stored in directories named by the latitude and longitude at which the mosaic is centered. Each directory contains a "browse" image, which shows the entire mosaic at reduced resolution, and 56 "tiles", which show the mosaic broken into smaller pieces of 7 rows by 8 columns. Each image consists of a pair of files, named *.img and *.lbl, the "image" and "label" files.

Each digital image is in VICAR format, the standard Jet Propulsion Laboratory format for digital imagery. VICAR stores individual pixels by row and column, with a single extra initial row describing the image in ASCII text. If you wish, you can read this first row (the "VICAR label") as text. You can also read as text the *.lbl file, which contains a complete description of the image file in a form which both you and your computer can understand. You can convert the imagery from VICAR into other formats (GIF, PICT, ...) for use with other software.

Getting Started

The first necessity is a CD-ROM reader. It is important that the drivers for the CD-ROM reader properly support the ISO-9660 standard. Older drivers which do not properly implement this standard will typically show the disks or subdirectories (folders) to be empty. Since drivers are specific to different CD-ROM readers, you should first contact your hardware supplier.

IBM-type personal computers need both a driver for the CD-ROM player and Microsoft's CD-ROM extensions for DOS. The driver is typically placed in the CONFIG.SYS file in your C:\ directory. The CD-ROM extensions are typically invoked through a batch file, either the AUTOEXEC.BAT file which runs as the computer starts, or a separate batch file run just before using the CD-ROM player. These two pieces of software use parts of the computer's memory, and may interfere with running other programs which use very large amounts of memory.

Macintosh computers need a set of CD-ROM files placed into their System folder in order to use the CD-ROM drive. After loading these files, the computer must be re-started, with the CD-ROM drive turned on before the computer itself. Since Macintosh CD-ROM drives are normally SCSI devices, it is important to avoid conflicts in the cabling, addressing, or termination with other SCSI devices connected to the computer.

Once you have the appropriate software installed, you can "open" the CD-ROM disk just as you would any other computer disk. On an IBM-type machine, you can change to the CD disk, change to a subdirectory, display the contents, or type a file. On a Macintosh, you can double-click on the CD icon to open the disk. CD-ROMs' particular strength is the amount of data they contain, rather than their speed. If you are going to work extensively with any file or image, it may be wise to copy it onto your hard disk first and use it there in order to speed up your work.

You might find it interesting that the Magellan CD-ROMs can actually be played in your audio CD player. Be sure to turn the volume down to minimum before you try this. The sound you hear will be a fairly loud buzz; it is the same data used to store the images for your computer, interpreted as though it were music.

What Are All These Files?

The Magellan CD-ROMs contain a number of files besides the image files themselves. The most useful is a file in the top directory of the CD named "AAREAD.ME", which describes the disk's contents in considerable detail. Like the other non-image files, it can be read with any word processor. If you are using a Macintosh, you may find that the file contains characters at the end of each line which the Macintosh doesn't recognize (linefeeds) and shows as "boxes". You can either ignore them, or remove them with your word processor.

Each disk contains a file which can act as an index of the named geologic features on Venus. This file can be loaded into a spreadsheet or database and used to locate features. (This function can also be performed using the special program from NSSDCA described above.) Each disk also has a set of the accumulated "problem reports" for earlier disks.

IBM-Type Personal Computers

IMDISP, the IBM-type personal computer image display software available from NSSDCA, should be loaded into a directory on your hard disk. This directory should be added to the "path" specified in your AUTOEXEC.BAT file, so that IMDISP can ben executed easily. Alternatively, use a batch file in a common batch directory which is on the path to locate and run IMDISP. The program is distributed in a compressed form which needs to be de-compressed with the program PKUNZIP before it can be run.

IMDISP works with IBM-type personal computers with at least EGA display cards. Much better results are obtained with VGA displays, and still better with Super-VGA displays. IMDISP can be adjusted to work with a variety of different Super-VGA displays, as explained in its documentation. To see the up-to-date list of displays supported, type "help set" at the IMDISP prompt. If your display system is one of those specifically listed, you can type "set display..." (where ... represents one of the possible choices, such as ATI800) at IMDISP's prompt to configure the display, or enter the line "set imdisp=..." in your CONFIG.SYS file. If your Super-VGA display is not one of those listed and you wish to experiment, type "set disp ..." and observe whether the screen is readable, or stays blank. If it stays blank, type "set disp vga" (in the blind) and the display will return. Work your way through the list until you find one which works.

IMDISP will use very large amounts of expanded memory if it is available. This memory will be used to buffer the data read from the CD-ROM, so that subsequent manipulation of the image is much faster. However, the program will run in machines with only 640K of memory.

To start the program, type "imdisp". Change drives to the CD-ROM drive just as you would in DOS. That is, if you set up the CD-ROM to be drive "H", type "H:" at the IMDISP prompt. Then type "files". Use the display of directory and file names to move to the image which you wish to view. If you wish at first to see only the browse images, rather than the long list of tiles, type "file browse.*". For the best performance, rather than selecting the *.img file which you wish to view, select the corresponding *.lbl file. The label file gives IMDISP extra information about the image which allows it to work more effectively.

If you are viewing a browse image, you may use the cursor (controlled by either the arrow keys or a mouse) to mark a particular region, and then ask IMDISP to call up the higher-resolution "tile" of the area selected. Type "cursor", move the cursor until it is on the area which interests you, and then hit the "period" key. Then type "disp source" to bring up the high resolution image centered on the cursor.

IMDISP allows a wide range of image processing procedures, including zooming, changing the brightness and contrast, and coloring the image. The command "help" and the IMDISP documentation explain these capabilities. In addition, IMDISP can be commanded to "browse" through all of a set of images (including the entire disk), or to perform a set of commands repeatedly in order to cycle through a display of images. IMDISP can save an image which has been processed, either as a VICAR image or in the GIF format, if the file name chosen is *.gif. The GIF format can be displayed on a very wide range of computers, including many inexpensive types.

Macintosh Computers

In order to display the Magellan images, you will need a Macintosh computer with at least an 8-bit color display card (although it may have a grey-scale monochrome display). You need the file "32-bit Quickdraw" in your System folder. You will also need as much memory as possible; at least 4 megabytes is recommended. Your computer should have a numeric co-processor. If not, it will be necessary to use a special file placed into your System folder to cause the computer to emulate the co-processor in software. Such emulation will reduce the speed of the program markedly.

Several programs are available for the Macintosh to display the Magellan images. The newest and most flexible is "Image4PDS" (Image for Planetary Data System CD-ROMs). This is a modified version of "Image 1.41", which was developed by the National Institutes of Health. The modification allows the program to open the Magellan images by "opening" the *.lbl file corresponding to the image. Unmodified versions of Image have difficulty opening the CD-ROM files directly.

Place the Image4PDS program into a folder on your hard disk. The program is distributed in compressed form and needs to be de-compressed with STUFFIT before it can be run. If you are running under Multifinder, it is wise to allocate as much memory as possible to Image through its Information box. When you first open Image, you may wish to adjust the sizes of the Cut and Paste buffers, set them as the default, and then restart the program. Large buffers are necessary if you wish to extract part of the image into a new image. Small buffers allow you to open large images in a machine with limited memory.

Use the "Open" command (Command-O) to select the CD-ROM drive, the desired folder, and the desired image. (Select the *.lbl, not the *.img file.) You can use normal Macintosh commands to adjust the size of the image window, or move it on the screen. A selection of "tools" lets you scroll the image within the window, adjust its brightness and contrast, change the magnification, and color the image. You can have multiple images open simultaneously in separate windows. Image lets you save the file in a number of formats, including PICT, which can be used by many different Macintosh programs.

Try Before You Buy

It is possible to try out some of the Magellan images even if you don't yet own a CD-ROM drive. You will need the display software from NSSDCA appropriate for your computer and either a modem or a connection to the Internet computer network. Alternatively, you may be able to ask a friend to copy the images onto a diskette for you. The limitation of this approach is that the Magellan image files are quite large, and therefore take time to move electronically (or fill diskettes quickly). CD-ROMs are particularly effective for distributing such large sets of data easily. Some sources of Magellan images are:


SPACELINK is intended to provide information useful for school teachers and contains a collection of digital images, as well as some of the "browse" images showing the standard mosaic images. SPACELINK's images are in GIF format, which helps to make them smaller and suitable for display on a variety of inexpensive classroom computers. They are accompanied by text files which give the captions released with the images. IMDISP will display the GIF images on IBM-type computers; a variety of GIF viewers exist for the Macintosh. You can connect to SPACELINK either through the Internet or by modem.

telnet: (
modem: (205) 895-0028

NASA's Ames Research Center

ARC llows public access through the Internet network to a large collection of information on NASA's missions, as well as image display software, digital image files in a variety of formats, and captions for all the released (press) images. Magellan imagery is available in GIF and VICAR formats. In addition, the Magellan CD-ROMs are available in rotation with other NASA image CD-ROMs as a pair of publicly accessible directories.
         ftp: (
        user:      anonymous

The PDS Geosciences Node at Washington University

This NODE permits access through the Internet network to selected Magellan data and documentation.
        ftp: (
       user:      anonymous
         cd:      /graphics/magellan

For Further Help

The best source for further help will depend on your problem, your location and what type of user you are.

Magellan Data Products Support Office

	Planetary Data System, Geosciences Node
	Earth and Planetary Remote Sensing Laboratory
     	Washington University, Campus Box 1169
     	One Brookings Drive
     	St. Louis, Missouri 63130-4899
     	(314) 935-5493, Fax:  (314) 935-7361
	E-mail:   WURST::MGNSO or

The Washington University PDS node provides a direct and knowledgeable source of assistance in using Magellan data through a Magellan Data Products Support Office. The purpose of the Support Office is to provide users with information about and assistance in getting Magellan data. Standard and special data products are supported, including digital products, photoproducts, slides, videotapes, and NASA Public Information Office (PIO) products. The Support Office serves NASA-sponsored scientists, other researchers and educators, and the general public.

The Support Office is staffed by researchers experienced in working with Magellan data products. The primary contact is Dr. Edward Guinness. The Office can answer questions such as what data products exist, where they can be obtained and at what cost, and how to read digital data products. The Office can provide the information necessary to complete an NSSDCA order form and will help users place an order.

In general, a user is referred to NSSDCA when the Support Office is certain that NSSDCA has the product in question. The Support Office gives the user the phone number and/or electronic mail address of NSSDCA, and helps the user determine exactly what to request. For a non-standard product, or when the Support Office is not certain that NSSDCA has a product, the Office tries to locate information about the product and then calls the user back. It then does whatever it can to help the user obtain the product.

NSSDCA personnel will refer a user to the Magellan Data Products Support Office in cases where they cannot help the user and know the Support Office can. If NSSDCA is not sure the Support Office has the answer, it will work directly with the Support Office to find the information, and then get back to the user.

The Support Office does not:

Dr. David R. Williams,
NSSDCA, Mail Code 690.1
NASA Goddard Space Flight Center
Greenbelt, MD 20771

NASA Official: Dave Williams,
Last Updated: 06 January 2005, DRW