NJPL1I00PDS100000000 = SFDU_LABEL RECORD_TYPE = STREAM OBJECT = TEXT NOTE = "Introduction to this CD-ROM volume." END_OBJECT END Voyagers to the Outer Planets Volume 12 - Neptune Images 12230.22 to 12457.33 in Compressed Format All Voyager Neptune Images in Browse Format This compact read-only optical disk (CD-ROM) is the last of four CD-ROM volumes containing all of the images taken by NASA's Voyager 2 spacecraft during its encounter with the planet Neptune in August, 1989. These 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 the images can be restored to their full resolution using algorithms described in documentation on this disk. Image decompression software in several programming languages is also included on the disk. The "Voyagers to the Outer Planets" CD-ROM set contains images from all the planets visited by the two Voyager spacecraft. This is the twelfth volume in the set. Volumes 1-3 contain all of the Voyager images taken during Uranus encounter; Volumes 4-5 contain selected images of Saturn; and Volumes 6-8 contain selected images of Jupiter. Volumes 9-11 contain the preceding parts of the Neptune image collection. This twelfth volume also contains all of the Voyager Neptune images in 'browse' format. Browse images consist of every fourth pixel of every fourth scan line, producing 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 a few files located in the main directory (another file, VOLDESC.SFD, contains general information similar to what you're reading 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 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 the Neptune 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 are executable decompression programs for IBM PC, Apple Macintosh and VAX VMS systems. The file named SOFTINFO.TXT in the SOFTWARE directory describes the software in detail. The compressed image files are contained in directories named after the principal target of the image. In alphabetical order, the main image directories for the Neptune volumes are: 1989N1 - Images of satellite 1989N1 1989N2 - Images of satellite 1989N2 NEPTUNE - Images of Neptune NEREID - Images of satellite Nereid N_RINGS - Images of the rings of Neptune TRITON - Images of satellite Triton In addition there are two catch-all directories containing images: CALIB - Calibration images OTHER - Images of stars and the sky background 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. See the document in file VOLINFO.TXT for further information about image numbers. 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 TRITON that contains all the browse format images of the satellite TRITON. 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 note that there are 1349 Voyager Neptune images that have a small error in their PDS labels. Whenever the value for the image attribute SCAN_MODE_ID should be '10:1', the value in the labels is actually given as '10:'. The values for SCAN_MODE_ID in the IMGINDEX.TAB index table correctly state the value as '10:1'.