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A Primer on Working with DOQs

A digital orthophoto is a digital image of an aerial photograph in which displacements caused by the camera and the terrain have been removed. It combines the image characteristics of a photograph with the geometric qualities of a map. The standard digital orhthophoto produced by the USGS is a black-and-white, or color infrared, 1-meter ground resolution quarter quadrangle image. The accuracy and quality of USGS digital orthophotos must meet National Map Accuracy Standards at 1:12,000 scale for 3.75-minute quadrangles and at 1:24,000-scale for 7.5-minute quadrangles. The accompanying information serves to help users to overcome some of the obstacles frequently encountered when working with DOQs. Material has been gathered from various USGS sources.

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About DOQs

The standard quarter-quadrangle image covers 3.75 minutes of latitude by 3.75 minute of longitude, at a scale of 1:12,000 cast on the Universal Transverse Mercator projection based on the North American Datum of 1983. Each image also has between 50 and 300 meters of overedge to facilitate tonal matching for mosaicking of adjacent images. Orthophotos combine the image characteristics of a photograph with the geometric qualities of a map. They serve a variety of purposes, from interim maps to field references for Earth science investigations and analyses. The digital orthophoto is useful as a layer of a geographic information system (GIS) and as a tool for revision of digital line graphs and topographic maps. Unlike a standard aerial photograph, relief displacement in orthophotos has been removed so that ground features are displayed in their true ground position. This allows for the direct measurement of distance, areas, angles, and positions. Also, an orthophoto displays features that may be omitted or generalized on maps. For more details about DOQs see this User Guide developed by the USGS NSDI Clearinghouse

Adobe Acrobat PDF Reader

Using New Header DOQs (keywords) in ARC/INFO and ARCVIEW

You can make use of several utilities for creating .hdr files for viewing DOQs in ARC/INFO or ARCVIEW.

You can use this AML routine for ARC 7.X doqnewhdr.aml

You can use this menu driven Windows program(95 or NT). Doq2Arc2.exe

You will need to ftp 3 other files:

Note: If your browser changes the .dll extension to .exe you must rename them for the program to work.

Here's how to prepare a DOQ to be read into ArcView. The information you need for the .hdr file (steps 2 and 3 below) is contained in the header of the DOQ. You can view this information by opening the DOQ file in a word processor, like wordpad. You can also create the .hdr file by using one of the utilities I have included in the links above. The example used here uses the "Napa_swm.doq" DOQ. The header file contained in it is attached below for you to follow along.
1. Naming of the DOQ image file:
- use .bil extension for single band gray scale images
- use .bip extension for 3 band color images
example: rename "napa_swm.doq" to "napa_swm.bil"

2. Create a text header file, it must be an ASCII text file:
- use the same name as the .bil but with a .hdr extension example "napa_swm.hdr"
- be sure the word processor doesn't add ".txt" at the end example "napa_swm.hdr.txt" won't work
3. Add lines to the .hdr text file that contain the following information:

nrows #number of rows or lines in image
ncols #number of columns or samples in image
ulxmap #upper left corner x value of pixel 1,1
ulymap #upper left corner y value of pixel 1,1
skipbytes #Number of bytes to skip that make up the header
xdim 1 #dimension of pixel in x direction
ydim 1 #dimension of pixel in y direction
nbands 1 #number of bands in image, nbands 3 for color images
nrows and ncols are "must have" values. They are contained in "SAMPLES_AND_LINES" in the DOQ header (LINES = nrows and SAMPLES = ncols)

ulxmap and ulymap are used to geo-reference the DOQ in UTM coordinates. They are contained in "XY_ORIGIN" in the DOQ header (the first value is X and the second value is Y)

skipbytes is used to avoid display of the header information found at the top of each DOQ. This value is called "BYTE_COUNT" in the DOQ header.

xdim and ydim refers to the dimension of the pixels, the default is 1 by 1. If you omit the xdim and ydim items you will see no change in your DOQ display.

nbands is 1 if the image is a gray scale image. For a color image nbands is 3 and the extension on the name of the DOQ should be .bip

So napa_swm.hdr looks like this:

nrows 7601
ncols 6221
ulxmap 554240.000
ulymap 4241020.000
skipbytes 6221
xdim 1
ydim 1
nbands 1
The following is the header information from "napa_swm.doq" data file:

QUADRANGLE_NAME               "NAPA"                
QUADRANT                      SW                    
WEST_LONGITUDE                -122 22 30.0          
EAST_LONGITUDE                -122 18 45.0          
NORTH_LATITUDE                  38 18 45.0          
SOUTH_LATITUDE                  38 15  0.0          
PRODUCTION_DATE               1997  9 15            
BAND_ORGANIZATION             "SINGLE FILE"         
BAND_CONTENT                  BLACK&WHITE           
BITS_PER_PIXEL                8                     
SAMPLES_AND_LINES             6221  7601            
HORIZONTAL_DATUM              NAD83                 
COORDINATE_ZONE               10                    
HORIZONTAL_UNITS              METERS                
HORIZONTAL_RESOLUTION         1.0                   
XY_ORIGIN                       554240.000  4241020.000          
SECONDARY_XY_ORIGIN             554336.454  4240823.773          
NATION                        US                    
STATE                         CA                    
NW_QUAD_CORNER_XY               554639.911  4240673.227          
NE_QUAD_CORNER_XY               560103.961  4240712.028          
SE_QUAD_CORNER_XY               560155.516  4233777.073          
SW_QUAD_CORNER_XY               554686.779  4233738.292          
SECONDARY_NW_QUAD_XY            554641.288  4240466.818          
SECONDARY_NE_QUAD_XY            560105.475  4240505.620          
SECONDARY_SE_QUAD_XY            560157.029  4233570.810          
SECONDARY_SW_QUAD_XY            554688.154  4233532.029          
RMSE_XY                          0.987              
IMAGE_SOURCE                  "Black and White film"
SOURCE_IMAGE_ID               "NAPP 6359-203"       
SOURCE_IMAGE_DATE             1993 7 6              
SOURCE_DEM_DATE               1980 1 1              
AGENCY                        "WESTERN MAPPING CENTER (WMC)"     
PRODUCER                      "Hammon, Jensen, Wallen & Associates"       
PRODUCTION_SYSTEM             "ORTHOVIEW"           
STANDARD_VERSION              1996 12               
METADATA_DATE                 1997  9 15            
DATA_FILE_SIZE                  47292042            
BYTE_COUNT                      6221                

Information on BARD's compressed DOQs

The compressed DOQs ( also known as COQs for Compressed Orthophoto Quadrangle ) range in size from 2.5 Megs to just over 5 Megabytes using JPEG compression. You can view the DOQs in Netscape after downloading by renaming the extension to jpg.

Programs available below are for the old DOQ header format

To use the DOQs in uncompressed format, if desired, you can uncompress them using the following JPEG decompression software
  • Version for DOS executed from the DOS prompt command line - djpeg.exe
  • Version for the Sun computer compiled under Solaris 2.7. - djpeg_sun.bin

    The Files Below are tar files with source code for compiling your own header manipulating routines. To compile your own version of a program that will read and display DOQ header information. To compile your own version of a program that will display and create a .hdr file on a windows 95 or NT system

    DOQ Standards (PDF)

    Standards for Digital Orthophotos - Contains preliminary pages and pages that briefly describe the various changes that have been made to the standard.

    Part 1: General, Standards for Digital Orthophotos - Provides general information on definitions, objectives, product description, sources, file structure, and format for digital orthophotos.

    Part 2: Specifications - Standards for Digital Orthophotos Defines the specifications for geographic extent, collection, processing, datums and coordinates, accuracy, ground sample distance, image radiometry, image mosaicking, data quality, header data, archiving, and distribution formats for digital orthophotos.

    Fact sheets from the USGS

    If you develop products, scripts, extensions, or translators for use with DOQQs and would like to make them available to the public, please send e-mail to If you have a paper, tutorial, or other useful document that we should refernce from here, please tell us about it.

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