Digital Orthophoto Quadrangles (DOQs), Minnesota, 1991-92

This page last updated: 01/08/2015
Metadata created using Minnesota Geographic Metadata Guidelines

Go to Section:
1. Overview
2. Data Quality
3. Data Organization
4. Coordinate System
5. Attributes
6. Distribution - Get Data
7. Metadata Reference

Section 1 Overview
Originator U.S. Geological Survey (USGS)
Title Digital Orthophoto Quadrangles (DOQs), Minnesota, 1991-92
Abstract This dataset contains rectified air photos flown during the spring of 1991 and 1992. They show ground conditions at the times they were collected.

A digital orthophoto is a raster image of remotely sensed data in which displacement in the image due to sensor orientation and terrain relief have been removed. Orthophotos combine the image characteristics of a photograph with the geometric qualities of a map. The primary digital orthophotoquad (DOQ) is a 1-meter ground resolution, quarter-quadrangle (3.75-minutes of latitude by 3.75-minutes of longitude) image cast on the Universal Transverse Mercator Projection (UTM) on the North American Datum of 1983 (NAD83). The geographic extent of the DOQ is equivalent to a quarter-quad plus overedge. The overedge ranges a minimum of 50 meters to a maximum of 300 meters beyond the extremes of the primary and secondary corner points. The overedge is included to facilitate tonal matching for mosaicking and for the placement of the NAD83 and secondary datum corner ticks. The normal orientation of data is by lines (rows) and samples (columns). Each line contains a series of pixels ordered from west to east with the order of the lines from north to south. The standard, archived digital orthophoto is formatted as four ASCII header records, followed by a series of 8-bit binary image data records. The radiometric image brightness values are stored as 256 gray levels ranging from 0 to 255. The metadata provided in the digital orthophoto contain a wide range of descriptive information including format source information, production instrumentation and dates, and data to assist with displaying and georeferencing the image. The standard distribution format of DOQs will be JPEG compressed images on CD by counties or special regions. The reconstituted image from the CD will exhibit some radiometric differences when compared to its uncompressed original but will retain the geometry of the uncompressed DOQ.
Purpose DOQs serve a variety of purposes, from interim maps to field references for earth science investigations and analysis. The DOQ is useful as a layer of a geographic information system and as a tool for revision of digital line graphs and topographic maps.
Time Period of Content Date 1992
Currentness Reference Air photos flown in Spring 1991 and Spring 1992. Ground condition.
Progress Complete
Maintenance and Update Frequency As needed
Spatial Extent of Data Minnesota
Bounding Coordinates -97.5
Place Keywords Minnesota, MN
Theme Keywords imageryBaseMapsEarthCover, DOQ, DOQQ, digital orthophoto, digital orthophotoquad, digital image map, aerial photograph, rectified photograph, rectified image, orthophoto, quarter-quadrangle orthophoto, 1-meter orthophoto
Theme Keyword Thesaurus ISO 19115 Topic Category
Access Constraints None
Use Constraints None. Acknowledgment of the U.S. Geological Survey would be appreciated in products derived from these data.
Contact Person Information Communications and Publishing,
U. S. Geological Survey
1400 Independence Road, MS 231
Rolla, MO  65401-2602
Phone: 573-308-3500
Fax: 573-308-3615
Browse Graphic None available
Associated Data Sets 1. 3-meter: Minnesota Dept. of Natural Resources has resampled the 1-meter DOQs to 3 meter resolution and mosaicked them into full quadrangle files. For more information and to download files, see:

2. 10-meter: The Minnesota Geospatial Information Office (MnGeo) has resampled the 1-meter DOQs to 10-meter resolution and mosaicked them into county files. For more information and to download files, see:

Section 2 Data Quality
Attribute Accuracy During photographic reproduction of the source photography, limited analog dodging is performed to improve image quality. Analog dodging consists of holding back light from certain areas of the sensitized photographic material to avoid overexposure. The diapositive is inspected to insure clarity and radiometric uniformity. Diapositive image brightness values are collected with a minimum of image quality manipulation. Image brightness values may deviate from brightness values of the original imagery due to image value interpolation during the scanning and rectification processes. Radiometry is verified by visual inspection of the digital orthophoto quadrangle with the original unrectified image to determine if the digital orthophoto has the same or better image quality as the original unrectified input image. Slight systematic radiometric differences can be detected between adjacent DOQ files due primarily to differences in source photography capture dates and sun angles of aerial photography along flight lines. These differences can be observed in an image's general lightness or darkness when compared to adjacent DOQ file coverages.
Logical Consistency All DOQ header data and image file sizes are validated by the Tape Validation System (TVS) software prior to archiving in the National Digital Cartographic Data Base (NDCDB). This validation procedure assures correct physical format and field values for header record elements. Logical relationships between header record elements are tested.
Completeness All DOQ imagery is visually inspected for completeness to ensure that no gaps, or image misplacement exists in the 3.75' image area or in overedge coverage. DOQ images may be derived by mosaicking multiple images, in order to insure complete coverage. All DOQs are cloud free within the 3.75' image area. Some clouds may, very infrequently, be encountered only in the overedge coverage. Source photography is leaf-off in deciduous vegetation regions. Void areas having a radiometric value of zero and appearing black may exist. These are areas for which no photographic source is available or result from image transformation from other planimetric systems to the Universal Transverse Mercator (UTM). In the latter case, the void sliver areas are on the outside edges of the overedge area. The data set field content of each DOQ header record element is validated to assure completeness prior to archiving in the NDCDB.

The area of coverage for a standard USGS digital orthophoto is either a quarter-quadrangle (3.75-minutes of latitude by 3.75-minutes of longitude plus overedge) or quadrangle (7.5-minutes of latitude by 7.5-minutes of longitude plus overedge). USGS requires image overedge to provide overlap coverage between adjoining DOQs to facilitate edge matching and mosaicking. That overedge extent is 300 (+/- 30) meters beyond the extremes of the primary and secondary datum corner points for the standard digital orthophoto quad. However, some Federal, State and local agencies, and private entities not associated with the National Digital Orthophoto Program (NDOP) may provide DOQs to the USGS under cooperative agreement programs. In order to meet the requirements of the NDOP program and include other sources of DOQs, the geographic extent for DOQs shall be:

* For DOQs produced under National Digital Orthophoto Program funding agreements: 300 (+/- 30) meters minimum beyond the extremes of the primary and secondary datum corner points.

* For DOQs produced under other cooperative agreements: a minimum of 50 meters beyond the primary and secondary horizontal datum corner point extremes.

The resulting digital orthophoto is a rectangle whose size may vary in relation to adjoining digital orthophotos.
Horizontal Positional Accuracy The DOQ horizontal positional accuracy and the assurance of that accuracy depend, in part, on the accuracy of the data inputs to the rectification process. These inputs consist of the digital elevation model (DEM), aerotriangulation control and methods, the photo source camera calibration, scanner calibration, and aerial photographs that meet National Aerial Photography Program (NAPP) standards. The vertical accuracy of the verified USGS format Elevation Model is equivalent to or better than a USGS level 1 or 2 DEM, with a root mean square error (RMSE) of no greater than 7.0 meters. Field control is acquired by third order class 1 or better survey methods sufficiently spaced to meet National Map Accuracy Standards (NMAS) for 1:12,000-scale products. Aerial cameras have current certification from the USGS, National Mapping Division, Optical Science Laboratory. Test calibration scans are performed on all source photography scanners. Horizontal positional accuracy is determined by the Orthophoto Accuracy (ORACC) software program for DOQ data produced by the National Mapping Division. The program determines the accuracy by finding the line and sample coordinates of the passpoints in the DOQ and fitting these to their ground coordinates to develop a root mean square error (RMSE). Four to nine points are checked. As a further accuracy test, the image line and sample coordinates of the DEM corners are transformed and compared with the actual X, Y DEM corner values to determine if they are within the RMSE. Additional information on this testing procedure can be found in U.S. Department of the Interior, U.S. Geological Survey, 1993, Technical Instructions, ORACC Users Manual (draft): Reston, VA. Adjacent DOQs, when displayed together in a common planimetric coordinate system, may exhibit slight positional discrepancies across common DOQ boundaries. Linear features, such as streets, may not be continuous. These edge mismatches, however, still conform to positional horizontal accuracy within the NMAS. Field investigations to validate DOQ positional accuracy reliability are periodically conducted by the USGS, National Mapping Division, Geometronics Standards Section. DOQs produced by cooperators and contractors use similarly approved RMSE test procedures.

For more information about DOQ accuracy, see:
Vertical Positional Accuracy Not applicable
Lineage The production procedures, instrumentation, hardware and software used in the collection of standard USGS DOQs vary depending on systems used at the contract, cooperator or USGS production sites. The majority of DOQ datasets are acquired through government contract. The process step describes, in general, the process used in the production of standard USGS DOQ data sets.

The rectification process requires a user parameter file as input to control the rectification process, a digital elevation model (DEM1) gridded to user specified bounds, projection, zone, datum and X-Y units, a scanned digital image file (PHOTO1) covering the same area as the DEM, ground X-Y-Z point values (CONTROL_INPUT) and their conjugate photo coordinates in the camera coordinate system, and measurements of the fiducial marks (CAMERA_INPUT) in the digitized image.

The camera calibration report (CAMERA_INPUT) provides the focal length of the camera and the distances in millimeters from the camera's optical center to the camera's 8 fiducial marks. These marks define the frame of reference for spatial measurements made from the photograph. Ground control points (CONTROL_INPUT) acquired from ground surveys or developed in aerotriangulation are third order class 1 or better and meet National Map Accuracy Standard (NMAS) for 1:12,000-scale. Ground control points are in the Universal Transverse Mercator or the State Plane Coordinate System on NAD83. Horizontal and vertical residuals of aerotriangulated tie-points are equal to or less than 2.5 meters. Standard aerotriangulation passpoint configuration consists of 9 ground control points, one near each corner, one at the center near each side and 1 near the center of the photograph, are used. The conjugate positions of the ground control points on the photograph are measured and recorded in camera coordinates.

The raster image file (PHOTO_1) is created by scanning an aerial photograph film diapositive with a precision image scanner. An aperture of approximately 25 to 32 microns is used, with an aperture no greater than 32 microns permitted. Using 1:40,000-scale photographs, a 25-micron scan aperture equates to a ground resolution of 1-meter. The scanner converts the photographic image densities to gray scale values ranging from 0 to 255 for black and white photographs. Scan files with ground resolution less than 1 meter or greater than 1 meter but less than 1.28 meters are resampled to 1 meter.

The principal elevation data source (DEM1) are standard DEM datasets from the National Digital Cartographic Data Base (NDCDB). DEM's that meet USGS standards are also produced by contractors to fulfill DOQ production requirements and are subsequently archived in the NDCDB. All DEM data is equivalent to or better than USGS DEM standard level 1. The DEM used in the production of DOQs generally has a 30-meter grid post spacing and possesses a vertical RMSE of 7 meters or less. A DEM covering the extent of the photograph is used for the rectification. The DEM is traversed from user-selected minimum to maximum X-Y values and the DEM X-Y-Z values are used to find pixel coordinates in the digitized photograph using transformations mentioned above. For each raster image cell subdivision, a brightness or gray-scale value is obtained using nearest neighbor, bilinear, or cubic convolution resampling of the scanned image. The pixel processing algorithm is indicated in the header file. An inverse transformation relates the image coordinates referenced to the fiducial coordinate space back to scanner coordinate space. For those areas for which a 7.5-minute DEM is unavailable and relief differences are less than 150 feet, a planar-DEM (slope-plane substitute grid) may be used.

Rectification Process: The photo control points and focal length are iteratively fitted to their conjugate ground control points using a single photo space resection equation. From this mathematical fit a rotation matrix of constants about the three axes of the camera is obtained. This rotation matrix can then be used to find the photograph or camera coordinates of any other ground X-Y-Z point. Next a two dimensional fit is made between the measured fiducial marks on the digitized photograph and their conjugate camera coordinates. Transformation constants are developed from the fit and the camera or photo coordinates are used in reverse to find their conjugate pixel coordinates on the digitized photograph.

Quality Control: All data is inspected according to a quality control plan. DOQ contractors must meet DOQ standards for attribute accuracy, logical consistency, data completeness and horizontal positional accuracy. During the initial production phase, all rectification inputs and DOQ data sets are inspected for conformance to standards. After a production source demonstrates high quality, inspections will be made to 10% of delivery lots 40 DOQs per lot). All DOQs are visually inspected for gross positional errors and tested for physical format standards.

Section 3 Spatial Data Organization (not used in this metadata)

Section 4 Coordinate System
Horizontal Coordinate Scheme Universal Transverse Mercator
UTM Zone Number 15
Horizontal Datum NAD83
Horizontal Units meters
Cell Width 1
Cell Height 1

Section 5 Attributes
Overview For DOQs from panchromatic source, each pixel contains an 8-bit gray-scale value between 0-255. Zero represents black, while 255 represents white. All values between 0 and 255 represent a shade of gray varying from black to white. For color-infrared and natural color DOQ's, a digital number from 0 to 255 will also be assigned to each pixel but that number will refer to a color look-up table which will contain the RGB red, blue and green (RGB) values, each from 0 to 255, for that digital number. Areas where the rectification process is incomplete due to incomplete data (i.e., lack of elevation data, gaps), are represented with the numeric value of 0.
Detailed Citation For more information about DOQ accuracy, see:
Table Detail:

Section 6 Distribution
Publisher U.S. Geological Survey
Publication Date unknown
Contact Person Information Communications and Publishing,
U. S. Geological Survey
1400 Independence Road, MS 231
Rolla, MO  65401-2602
Phone: 573-308-3500
Fax: 573-308-3615
Distributor's Data Set Identifier USGS 1991-92 DOQs
Distribution Liability Although these data have been processed successfully on a computer system at the U.S. Geological Survey, no warranty, expressed or implied, is made by the USGS regarding the utility of the data on any other system, nor shall the act of distribution constitute any such warranty. The USGS will warrant the delivery of this product in computer-readable format and will offer appropriate adjustment of credit when the product is determined unreadable by correctly adjusted computer input peripherals, or when the physical medium is delivered in damaged condition. Requests for adjustments of credit must be made within 90 days from the date of this shipment from the ordering site.

MnGeo's data disclaimer is online:
Ordering Instructions 1. Access the photos through a web mapping service (WMS) from the Minnesota Geospatial Information Office (MnGeo):

2. Order or view the photos from USGS:
Online Linkage I AGREE to the notice in "Distribution Liability" above. Clicking to agree will either begin the download process, link to a service, or provide more instructions. See "Ordering Instructions" above for details.

Section 7 Metadata Reference
Metadata Date 01/08/2015
Contact Person Information Nancy Rader, GIS Data Coordinator
Minnesota Geospatial Information Office (MnGeo)
658 Cedar Street
St. Paul, MN  55155
Phone: 651-201-2489
Metadata Standard Name Minnesota Geographic Metadata Guidelines
Metadata Standard Version 1.2
Metadata Standard Online Linkage

This page last updated: 01/08/2015
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