Voyagers to the Outer Planets 3: Uranus/VoyagestotheOuterPlanetsVol3.cdr/aareadme.txt

Text File | 1988-10-25 | 7KB | 137 lines

NJPL1I00PDS100000000 = SFDU_LABEL
RECORD_TYPE          = STREAM
OBJECT               = TEXT
  NOTE               = "Introduction to this CD-ROM volume."
END_OBJECT
END


                     Voyagers to the Outer Planets

                           Volume 3 - Uranus

            Images 26951.07 to 27628.47 in Compressed Format
                                 and
               All Voyager Uranus Images in Browse Format


This compact read-only optical disk (CD-ROM) is the third of three CD-ROM
volumes containing the images returned by NASA's Voyager 2 spacecraft
during its encounter with the planet Uranus.  Future volumes in the
"Voyagers to the Outer Planets" series will contain images from the
other planets visited by the twin Voyager spacecraft.

There are two groups of images on this disk. The first group consists of
images taken during the post-encounter phase, as the Voyager 2 spacecraft
was departing the vicinity of Uranus. These images are the full-resolution
(800 pixels by 800 scan lines) digital images returned by the Voyager
cameras. No additional processing has been performed to enhance the images.
The images are compressed to permit us to pack more data onto each volume
but they can be restored to their original resolution using algorithms
described in documentation on this disk. Image decompression software in
several programming languages is also included on the disk. This group of
images completes the collection of full-resolution images that began with
the two previous Voyager Uranus CD-ROM volumes. The first volume contains
images taken during Voyager 2's approach to Uranus and the second volume
contains images taken during the spacecraft's closest approach to the
planet in January 1986.

The second group of images on this disk was produced by converting all of
the Voyager images taken at Uranus to a special 'browse' format.  Browse
images consist of every fourth pixel of every fourth scan line, resulting
in an image of 200 pixels by 200 scan lines.  You can use browse images to
quickly locate an image of interest to you and then go back to the
compressed version of the image to get the full 800 pixel by 800 scan
line resolution.


As you may have noticed, the file that you are reading now is one of only
two files located in the main directory (the other file, VOLDESC.SFD,
contains general information similar to what you are reading now but in a
format that is easier for computer programs to access). All other files
are located in directories below the main directory. The directory named
DOCUMENT contains a document file named VOLINFO.TXT that describes in
detail the organization of this disk and the format and content of the
Voyager Uranus images. It is highly recommended that you read the VOLINFO
document before trying to process image files.

The directory named INDEX contains a file IMGINDEX.TAB which is an index
to all of the Uranus images. The index table is human and machine readable.
While you can locate images by simply searching through the index yourself,
the table has been designed so that it can be easily loaded into most
database managers for fast and efficient searching.  The file named
INDXINFO.TXT in the INDEX directory describes the index table in detail.

The directory named SOFTWARE contains source and executable versions of
image decompression software written in Fortran, C and VAX Macro assembly
language.  There is one executable decompression program for IBM PCs and
another for VAX VMS systems. The file named SOFTINFO.TXT in the SOFTWARE
directory describes the software in detail.

Each compressed full-resolution image is contained in a file and the
compressed image files are located in directories named after the
principal target of the image. In alphabetical order the directories
containing compressed images on the Uranus volumes are:

  ARIEL            - Images of satellite Ariel
  MIRANDA        - Images of satellite Miranda
  OBERON        - Images of satellite Oberon
  TITANIA        - Images of satellite Titania
  UMBRIEL        - Images of satellite Umbriel
  URANUS        - Images of Uranus
  U_RINGS        - Images of the rings of Uranus

In addition there are two catch-all directories containing compressed
images:

  CALIB                 - Calibration images
  OTHER                 - Images that don't fit in any other category

If there are no images of a target on a particular volume then the target's
directory is omitted.  If there are more than about 100 images of a target
on a volume, the images are further divided into subdirectories based upon
their image number. Each image subdirectory has a name of the form CnnnnXXX,
where nnnn is the first four digits of the seven-digit image number.  All
images of the target with image numbers that have those first four digits
will appear in the subdirectory.

Each browse image is contained in a file and the browse image files are
arranged into directories using the scheme outlined above for compressed
images. The only difference is that all of the browse image directories
are located under the directory named BROWSE. Within the BROWSE directory
you will find, for example, a subdirectory named ARIEL that contains all
the browse format images of the satellite Ariel.

Most files on this disk have a label encoded in the Object Description
Language (ODL).  A file's ODL label is readable by both humans and
computers and it provides a formal description of the format and
content of the file.  For most files the ODL label appears at the
beginning of the file (this is the case for the file that you are
currently reading).  All image files have such an embedded ODL label
preceding the data in the file.  For files where labels can't be easily
included, a separate label file is provided that contains the ODL label
and a pointer to the file that the label describes.  These external
label files all have a .LBL file extension.  An example of an external
label is the file IMGINDEX.LBL in the INDEX directory which contains
the ODL label for the index file IMGINDEX.TAB.  The LABEL directory
contains two files with external ODL labels that describe the format
and content of the engineering information that is contained within
each image file. For a description of the Object Description Language,
see the document file VOLINFO.TXT in the DOCUMENT directory.


Please be aware that there are several problems with the first Voyager
Uranus CD-ROM volume.  Firstly, 76 images of Uranus were placed into the
wrong subdirectory: these images all have image numbers beginning with
the digits 2624 and hence they should have been placed into a subdirectory
named C2624XXX under the URANUS directory; but due to a juxtaposition of
digits they are instead located in the subdirectory C2264XXX. Secondly the
image file C2625405.IMQ is missing from the disk. Thirdly, the image file
C2449031.IMQ was truncated during processing and the image cannot be
decompressed.  We have updated the IMGINDEX.TAB file found on Uranus
Volumes 2 and 3 to point to the actual location of the 76 misplaced files.
We have also placed the missing file and the truncated file onto Volume 2
and updated the IMGINDEX.TAB files on Volumes 2 and 3 to reflect this. We
suggest that you use the index file found on Volumes 2 and 3 in preference
to the index file on Volume 1.