The two raster mosaics were constructed using MrSID compressed images and ArcCatalog 8.2. They are stored in the SDE database with JPEG compression. This means that the original TIFFs have been compressed twice with a lossy compression algorithm - first in the original conversion of TIFF to MrSID format and second in the conversion from MrSID to an SDE raster using JPEG compression. The images are also resampled in the mosaicking process. This procedure is not recommended. The raster data would have been much better preserved if the original TIFFs had been imported directly into SDE and stored with LZ77 (non-lossy) compression. The less optimal procedure was used, however, due to the very large amounts of data involved and the limited resources available to do the processing. The 2 JPEG-compressed data sets consume 50 gigabytes in the SDE database. If LZ77 compression were used the data would consume 250 gigabytes. The MrSID data were in-processed in less than a week in a fully automated process using on-line data. Using the original TIFF data would have entailed manual handling and loading of data from approximately 250 CD-ROMs and several additional weeks of effort.
The metadata provided in the table named GISDB.IL_DOQ_NAPP3_METADATA_TB contain a wide range of descriptive information such as format source information, production instrumentation and dates.
There are a few NAPP2 DOQs included west of the Illinois state boundary. They are external to Illinois but were included to complete a small buffer area around the outside of the state. They can be identified by referring to the NAPP field of the associated metadata table (GISDB.IL_DOQ_NAPP3_METADATA_TB).
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 the overedge, which ranges a minimum of 50 meters to a maximum of 300 meters beyond the extremes of the primary (NAD83) and secondary (NAD27) corner points. The overedge is included to facilitate tonal matching for mosaicking and for the placement of primary 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 USGS 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 modified, compressed ISGS digital orthophotos from which this raster mosaic was derived are black-and-white images in MrSID format with an approximate compression ratio of 15:1.
These data are appropriate for use in local and regional thematic analysis. The data are not appropriate as a geodetic, legal or engineering base. The data set serves as an important base cartographic element for many types of maps and has been widely distributed and used outside the ISGS. The data set was not and is not intended as a substitute for surveyed locations, such as can be determined by a registered Public Land Surveyor. Although useful in a GIS as a reference base layer for maps, the data set has no legal basis in the definition of boundaries or property lines.
Links to these are provided in the Cross References section.
Individuals or entities may make fair use of copyrighted ISGS material, such as reproducing a single figure or table, or using a brief text quotation, without obtaining formal permission, but in all cases the Illinois State Geological Survey must be credited as the source of the material. To reproduce ISGS information beyond the fair use standard, permission must be obtained from the ISGS Information Office, 615 East Peabody Drive, Champaign, Illinois 61820, 217-333-4747, firstname.lastname@example.org. License fees and a license agreement may be required, depending on the proposed usage.
Map information is to be used at a scientifically and cartographically appropriate scale, that is, at a scale no greater than indicated on the map or as described in the documentation of the map or map data. Map information is not appropriate for, and is not to be used as, a geodetic, legal, or engineering base. Map information has no legal basis in the definition of boundaries or property lines and is not intended as a substitute for surveyed locations such as can be determined by a registered Public Land Surveyor.
The data do not replace the need for detailed site-specific studies.
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.
For modified, compressed DOQs (MrSID format) developed by ISGS:
Image brightness and contrast has been enhanced for a more aesthetic and useful look since the original imagery was rather dark. This adjustment was conducted in image processing software, PCI. The resultant, modified image was compressed using MrSID at a target compression ratio of 15:1. MrSID is not lossless compression, however image degradation is only noticeable with extremely fine detail (i.e. plowing patterns in agricultural fields) when zoomed in to a level where the original imagery begins to pixelate.
For SDE DOQ mosaic developed by ISGS:
This raster mosaic was constructed using MrSID compressed images and ArcCatalog 8.2. They are stored in the SDE database with JPEG compression. This means that the original TIFFs have been compressed twice with a lossy compression algorithm - first in the original conversion of TIFF to MrSID format and second in the conversion from MrSID to an SDE raster using JPEG compression. The images are also resampled in the mosaicking process. This is not an optimal procedure, but was used due to the very large amounts of data involved and the limited resources available to do the processing. Image degradation is only noticeable with extremely fine detail (i.e. plowing patterns in agricultural fields) when zoomed in to a level where the original imagery begins to pixelate.
The SDE mosaic also shows more contrast than the source MrSID images, giving a grainier appearance, because the in-processing negates some of the contrast enhancements that were applied with PCI software. This can be corrected in ArcGIS software by using a Minimum-Maximum stretch in the ArcMap symbology properties for the data layer.
No subsequent logical validation has been performed.
All original DOQ imagery was visually inspected by the USGS for completeness to ensure that no gaps, or image misplacement exist 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 DOQ's 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.
Regarding DOQs and DOQ mosaic as subsequently processed by ISGS:
All areas in the state of Illinois are represented. Five quarter-quadrangles in southern and southwestern Illinois are derived from NAPP2 DOQs. These can be determined using the associated metadata table.
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 DEM 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). From 4 to 9 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 DOQ's, 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. DOQ's produced by cooperators and contractors use similarly approved RMSE test procedures.
For SDE DOQ mosaic developed by ISGS:
Once the mosaic was generated, the data had been compressed twice and resampled once. This has a likelihood of applying slight gray-shade shifts to any given pixel. It is unlikely the gross location of large objects (those composed of several pixels) was significantly changed in this process.
The rectification process requires, as input, a user parameter file 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 DOQ's 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 centered on the DOQ coverage area. 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.
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 is obtained a rotation matrix of constants about the three axes of the camera. 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.
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 DOQ's are visually inspected for gross positional errors and tested for physical format standards.
Softcopy in ASCII format is available at: <URL:ftp://www-nmd.usgs.gov/pub/ti/DOQ/doqstnds/stdoqpt1.txt> <URL:ftp://www-nmd.usgs.gov/pub/ti/DOQ/doqstnds/stdoqpt2.txt>
Softcopy in WordPerfect format is available at: <URL:ftp://www-nmd.usgs.gov/pub/ti/DOQ/doqstnds/stdoqpt1.wp5> <URL:ftp://www-nmd.usgs.gov/pub/ti/DOQ/doqstnds/stdoqpt2.wp5>
Softcopy in PostScript format is available at: <URL:ftp://www-nmd.usgs.gov/pub/ti/DOQ/doqstnds/stdoqpt1.ps> <URL:ftp://www-nmd.usgs.gov/pub/ti/DOQ/doqstnds/stdoqpt2.ps>
Softcopy in hypertext is available at: <URL:ftp://www-nmd.usgs.gov/pub/doq_html/standards_doq.html>
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Illinois Natural Resources Geospatial Data ClearinghouseGenerated by mp version 2.8.25 on Wed Apr 08 13:23:40 2009