File:  A_README.TXT
May 4, 1994


INTRODUCTION TO THIS DISC


This Compact Disc-Read Only Memory (CD-ROM) was produced by the U.S.
Geological Survey (USGS).  It contains all digital orthophoto quadrangle
(DOQ) images necessary to cover Philadelphia County, Pennsylvania and may 
include adjacent quadrangles.  For a general introduction to digital 
orthophotos, select "Introduction to DOQ Data" from the MAIN MENU.


Menu System

This CD-ROM includes a text-based user interface, commonly called a menu 
system, for MS-DOS-compatible computers.  The interface is designed to 
facilitate access to and use of text and image files.  To invoke the user 
interface from the system prompt, enter: DOQ (in either upper case or 
lower case).  For more information on the menu system, select "Menu System" 
from the DOCUMENTATION MENU.


Image Compression

CD-ROM's are capable of storing approximately 700 megabytes of digital
information.  It was necessary to compress each image to facilitate 
distribution on a single disc.  The data files on this disc were compressed 
using software developed by the Independent Joint Photographic Experts Group 
(JPEG).  Files compressed with JPEG software are not useful until they are 
decompressed.  Many shareware, public domain, and commercially available 
image display and image processing programs include JPEG decompression 
software. JPEG compression and decompression programs are also provided on 
this disc. For current information on JPEG software and its use, select 
"JPEG" from the DOCUMENTATION MENU.  

Image display or image processing programs are not contained on this disc.


Directory Structure

The menu system on this CD-ROM is designed to aid in the selection and 
display of text files, to facilitate the use of JPEG software, and to 
assist in navigating this disc.  For those who prefer to explore the disc 
contents without using a menu system, or for users of operating systems 
other than MS-DOS, the directory structure is shown below.

 root:              ***CD-ROM for USGS DOQ's***
    |
    |___DATA      (DOQ data files; Header Records and Compressed Files)
    | 
    |___DOCUMENT  (Information on USGS contacts and ordering data)
    |   |
    |   |___DISCINFO  (Information about this disc)
    |   |___DOQINFO   (Information particular to DOQ's and their production)
    |   |___GSMENU    (Information on using the menu system)
    |   |___JPEG      (Information about JPEG and its usage)
    |
    |___SOFTWARE
        |
        |___DOSMENU   (GSMENU software and files utilized by the menu system)
        |
        |___JPEG
            |
            |___DG_UNIX  (Data General UNIX executables)
            |___MS_DOS   (MS-DOS executables)
            |___SOURCE   (C-program language source code)
    
      
The root directory contains a text file titled STARTUP.HLP that
includes a brief introduction to disc usage and directs the reader to 
other helpful files on the disc.  Also in the root directory is the 
DOQ batch file (DOQ.BAT) that invokes the MS-DOS menu system.  All text 
files on this disc are in ASCII format.  For a complete description of 
the files contained in disc subdirectories, select "File Descriptions" 
from the MAIN MENU.

The \DOCUMENT sudirectory contains a USGS contact list, ordering
information, and four subdirectories:  \DISCINFO, \DOQTEXT, \GSMENU, 
\JPEG.  Information about the CD-ROM and the files contained on it are 
located in \DISCINFO.  Information about DOQ production, accuracy, 
technical standards, and compression are found in \DOQTEXT.  \DOQTEXT 
also contains a file listing DOQ coordinates and data set names, as well 
as a file describing the USGS DOQ program.  MS-DOS users can display all 
text files on this disc by making menu selections.  MS-DOS users can 
print any files that are displayed by pressing F4.  Users of other
operating systems must use their own text display or editing software.  
\GSMENU contains documentation for the menu system software and menu help 
files.  Documentation files for JPEG software are located in \JPEG, as 
well as additional information on using the default output format.

The \SOFTWARE subdirectory contains two subdirectories:  \DOSMENU and 
\JPEG.  The programs used to devise and run the text-based user interface 
are contained in \DOSMENU.  Programs to decompress and compress DOQ image 
files are contained in \JPEG.  The \JPEG subdirectory is subdivided into 
three subdirectories:  \MSDOS, \SOURCE, and \DGUNIX.  The \MSDOS 
subdirectory includes JPEG software for users of IBM-compatible computers; 
the DGUNIX subdirectory includes JPEG software for Data General Aviion 
workstations used by the USGS in the production of digital orthophoto 
quadrangles.  The \SOURCE subdirectory contains C-program language 
makefiles.  These generic files can be configured and compiled for use 
on other computers.

The \DATA subdirectory contains all USGS compressed digital orthophoto
quadrangles and their associated file headers.  The contents of the file
headers is described in "Standards for Digital Orthophotos" (USGS National 
Mapping Program Technical Instructions).  This document is viewed by 
selecting "Standards for DOQ Data" from the DOCUMENTATION MENU.