FAIRFAX COUNTY 2001 DIGITAL ORTHOPHOTOGRAPHY

Section Index

Identification_Information
Data_Quality_Information
Spatial_Data_Organization_Information
Spatial_Reference_Information
Distribution_Information
Metadata_Reference_Information

Identification Information

Section Index

    Citation:
      Citation Information:
        Title: Fairfax County 2001 Digital Orthophotography
    Description:
      Abstract:
        These data contain high quality color digital orthophotography updates at multi-level resolutions ranging from 0.5', 1', 2' in multiple of 2 to 512' pixel resolutions within the boundary the Northwest corner of Fairfax County, hereinafter referred to as Sub-Block 1. These data include cities and townships completely within the geographic area, which encompasses approximately 133 square miles. The updates involve a total of 233 of the eight-foot pixel tiles (4096'x4096'). Information includes changes and updates in the digital terrain model (DTM) to support 2' and 5' contour intervals, break lines, and mass points within the designated boundary.
      Purpose:
        Fairfax County has a requirement to partially update its current digital orthophoto database by replacing approximately 133 square miles of imagery with new color digital orthophotos in areas of substantial developmental change.
      Supplemental Information:
        The updated digital orthophoto (DO) images were produced from the airborne GPS-supported Aerial Triangulated controlled 1"=660' scale color photography. A total of 576 exposures and 15 spot shots were collected from the AGPS. There were approximately 56 signalized control points utilized including 10 eccentric points in the NW area. Each DO tile was created in a specific and consistent manner from updated DTM and 17 micron scanned imagery. All data is geo-referenced and quality controlled using Geospatial Accuracy Standards Part 3: National Standards for Spatial Data Accuracy (NSSDA). The updated DO imagery and DTM data is integrated into the County Tax Map grid system. Digital Aerial Traiangulation (DAT) was accomplished using the Inpho MATCH-AT aerial triangulation software.
        DO production was accomplished using KLT Atlas software.
        Image clean-up (artifacts) was accomplished using a combination of Adobe Photoshop and OrthoVista software.
    Time Period of Content:
      Time Period Information:
        Multiple Dates/Times:
          Single Date/Time:
            Calendar Date: 3/12/2001
          Single Date/Time:
            Calendar Date: 3/19/2001
          Single Date/Time:
            Calendar Date: 3/25/2001
          Single Date/Time:
            Calendar Date: 3/27/2001
      Currentness Reference: ground condition
    Status:
      Progress: Complete
      Maintenance and Update Frequency:
        The county has undertaken a photogrammetric database update program, systematically updating incrementally in a four-year cycle. Both the need and the funds available will be considered in how often this area will be updated.
    Spatial Domain:
      Bounding Coordinates:
        West Bounding Coordinate: -77.54533008
        East Bounding Coordinate: -77.03408065
        North Bounding Coordinate: 39.0804078
        South Bounding Coordinate: 38.61389198
      Data Set G-Polygon:
        Data Set G-Polygon Outer G-Ring:
          G-Ring Point:
            G-Ring Latitude: 39.0804078
            G-Ring Longitude: -77.54533008
          G-Ring Point:
            G-Ring Latitude: 38.61389198
            G-Ring Longitude: -77.54533008
          G-Ring Point:
            G-Ring Latitude: 38.61389198
            G-Ring Longitude: -77.54533008
          G-Ring Point:
            G-Ring Latitude: 39.0804078
            G-Ring Longitude: -77.03408065
          G-Ring Point:
            G-Ring Latitude: 39.0804078
            G-Ring Longitude: -77.54533008
    Keywords:
      Theme:
        Theme Keyword Thesaurus: None
        Theme Keyword: Aerial Photography (AP)
        Theme Keyword: Digital Orthophotography (DO)
        Theme Keyword: Digital Aerial Triangulation (DAT)
        Theme Keyword: Digital Orthophoto Imagery
        Theme Keyword: Airborne GPS (AGPS)
      Place:
        Place Keyword Thesaurus: None
        Place Keyword: Fairfax County, Virginia, USA
    Use Constraints:
      This data is only updated every four years. Therefore this data should not be relied upon for 100% accuracy at any time. Contact officials with the Fairfax county GIS department for information on the most accurate areas. The GIS Department of Fairfax County should acknowledge use of this information for the development of products.
    Point of Contact:
      Contact Information:
        Contact Organization Primary:
          Contact Organization: Fairfax County GIS and Mapping Services
        Contact Position: Database Administrator
        Contact Address:
          Address Type: mailing and physical address
          Address: 12000 Government Center Pw. Suite 117
          City: Fairfax
          State or Province: VA
          Postal Code: 22035
          Country: USA
        Contact Voice Telephone: (703)-324-2712
        Contact TDD/TTY Telephone: 711
        Contact Facsimile Telephone: (703)-324-3937
        Contact Electronic Mail Address: gis.helpq@fairfaxcounty.gov
        Hours of Service: Monday 8:00am - 4:15pm / Tuesday 9:00am - 4:15pm / Wednesday - Friday 8:00am - 4:15pm (EST)
    Data Set Credit: Landata created the data set under contract to Fairfax County. Landata and staff from the County of Fairfax GIS Branch performed quality control checks.
    Native Data Set Environment:
      Erdas lan format files for uncompressed ortho catalog. MrSid format files for compressed ortho catalog.
      G:\raster\mrsid\2001sid05.dbf - 0.5 foot resolution
      G:\raster\mrsid\2001sid1.dbf - 1 foot resolution
      G:\raster\mrsid\2001sid2.dbf - 2 foot resolution

Data Quality Information

Section Index

    Completeness Report:
      All the digital data of the project is presented in a seamless manner in one single file for pixel resolutions of 16', 32', 64', 128' and 256'. There are 164 tiles (some tiles at the County boundary contain partial image coverage) at 6 inch pixel resolution. Each tile is of 4096' x 4096' dimensions.
    Positional Accuracy:
      Horizontal Positional Accuracy:
        Horizontal Positional Accuracy Report:
          Framework digital orthoimagery accuracy employed the National Standard for Spatial Data Accuracy (NSSDA), which implements a statistical and testing methodology for estimating the geopositional accuracy of digital point data, with respect to their ground positions measured with higher accuracy. The entire project was tested per the NSSDA standards. This reporting methodology provides a common language for reporting positional accuracy so that users can evaluate data sets for appropriate use for their applications. The NSSDA uses root-mean-square error (RMSE) to estimate positional accuracy. Accuracy is reported in ground distances at the 95% confidence level. Accuracy reported at the 95% confidence level means that 95% of the positions in the data set will have an error with respect to true ground position that is equal to or smaller than the reported accuracy value. The reported accuracy value reflects all uncertainties, including those introduced by geodetic control coordinates, compilation, and final computation of ground coordinate values in the product.
          Fairfax County 2001 Update project was completed to Accuracy Standards for Large Scale Maps, ASPRS. The project accuracy standards also meet Virginia State Mapping Standards which are quite identical to ASPRS Accuracy Standards for Large Scale Maps.

          Geometric accuracy checking was accomplished by measuring the coordinates of well-defined photo identifiable features within 20% of the 8-foot pixel tiles (44 tiles) with a view to these features being included in the DAT block adjustment. A comparison was made between the DAT coordinate values and the coordinate values of the same features as extracted (screen measurements) from the final digital orthophoto image. A total of 20 sample points were measured from a composite block comprising of 4 selected adjacent 8-foot pixel tiles at an average of 5 points per tile. This accuracy check is referred to as the ‘DO Geometric Accuracy Check' and each test is NSSDA compliant.

          The QC accuracy checks using 6 resolution imagery indicate that the geometric accuracy obtained was consistent with 1:1200 mapping accuracy standards.

          To determine the measurement accuracy for a specific resolution, multiply the resolution by a factor of 2. For instance, measuring distances on 2 foot resolution ortho image the expected error in distance may be plus or minus 4 feet.
      Vertical Positional Accuracy:
        Vertical Positional Accuracy Report:
          DTM (vertical) accuracy checking was accomplished by measuring the elevation of well defined photo identifiable features in the high accuracy DAT block adjustment. A comparison was made between the DAT elevation values and the elevation values of the same features as extracted from the TIN file associated with each 8-foot pixel tile for which the check was performed. These tests were conducted in about 20% of the project area by selecting features within an 8 foot pixel tiles (44 tiles). A total of 20 sample points were used measured from a composite block comprising of 4 selected adjacent 8-foot pixel tiles at an average of 5 points per tile. This accuracy check is referred to as the ‘DTM Accuracy Check' and is NSSDA compliant.
          The QC accuracy checks indicate that the vertical accuracy obtained for those areas that underwent DTM updating was consistent with 2' contour accuracy standards.
    Lineage:
      Source Information:
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        Source Citation Abbreviation: Image 24
      Process Step:
        Process Description: Design aerial photo flight line configuration THE CONTACT AND THE PROCESS DATE IS THE SAME FOR ALL THE PROCESS STEPS IN THE DATA QUALITY INFORMATION SECTION.
        Source Used Citation Abbreviation: Image 1
        Source Produced Citation Abbreviation: Image 2
        Process Contact:
          Contact Information:
            Contact Organization Primary:
              Contact Organization: Fairfax County GIS and Mapping Services
            Contact Position: Database Administrator
            Contact Address:
              Address Type: mailing and physical address
              Address: 12000 Government Center Pw. Suite 117
              City: Fairfax
              State or Province: VA
              Postal Code: 22035
              Country: USA
            Contact Voice Telephone: (703)-324-2712
            Contact TDD/TTY Telephone: 711
            Contact Facsimile Telephone: (703)-324-3937
            Contact Electronic Mail Address: gis.helpq@fairfaxcounty.gov
            Hours of Service: Monday 8:00am - 4:15pm / Tuesday 9:00am - 4:15pm / Wednesday - Friday 8:00am - 4:15pm (EST)
      Process Step:
        Process Description: Signalize ground control points
        Source Used Citation Abbreviation: Image 2
        Source Produced Citation Abbreviation: Image 3
      Process Step:
        Process Description: Establish AGPS base station locations
        Source Used Citation Abbreviation: Image 3
        Source Produced Citation Abbreviation: Image 4
      Process Step:
        Process Description: Fly aerial photography (AP), process aerial photography
        Source Used Citation Abbreviation: Image 4
        Source Produced Citation Abbreviation: Image 5
      Process Step:
        Process Description: Process AGPS data
        Source Used Citation Abbreviation: Image 5
        Source Produced Citation Abbreviation: Image 6
      Process Step:
        Process Description: Perform AP and AGPS QA/QC
        Source Used Citation Abbreviation: Image 6
        Source Produced Citation Abbreviation: Image 7
      Process Step:
        Process Description: Scan aerial negatives
        Source Used Citation Abbreviation: Image 7
        Source Produced Citation Abbreviation: Image 8
      Process Step:
        Process Description: Check scanner calibration (scanned image fiducial residuals)
        Source Used Citation Abbreviation: Image 8
        Source Produced Citation Abbreviation: Image 9
      Process Step:
        Process Description: Convert scanned color images to black and white for DAT procedures
        Source Used Citation Abbreviation: Image 9
        Source Produced Citation Abbreviation: Image 10
      Process Step:
        Process Description: Create image pyramids
        Source Used Citation Abbreviation: Image 10
        Source Produced Citation Abbreviation: Image 11
      Process Step:
        Process Description: Perform interior orientation on images
        Source Used Citation Abbreviation: Image 11
        Source Produced Citation Abbreviation: Image 12
      Process Step:
        Process Description: Input A priority weights for DAT
        Source Used Citation Abbreviation: Image 12
        Source Produced Citation Abbreviation: Image 13
      Process Step:
        Process Description: Locate and observe all ground control points
        Source Used Citation Abbreviation: Image 13
        Source Produced Citation Abbreviation: Image 14
      Process Step:
        Process Description: Perform level 1 block adjustment
        Source Used Citation Abbreviation: Image 14
        Source Produced Citation Abbreviation: Image 15
      Process Step:
        Process Description: Run DAT adjustment
        Source Used Citation Abbreviation: Image 15
        Source Produced Citation Abbreviation: Image 16
      Process Step:
        Process Description: Produce DAT report
        Source Used Citation Abbreviation: Image 16
        Source Produced Citation Abbreviation: Image 17
      Process Step:
        Process Description: Select QA/QC check points
        Source Used Citation Abbreviation: Image 17
        Source Produced Citation Abbreviation: Image 18
      Process Step:
        Process Description: Update 1997 DTM
        Source Used Citation Abbreviation: Image 18
        Source Produced Citation Abbreviation: Image 19
      Process Step:
        Process Description: Create DO data
        Source Used Citation Abbreviation: Image 19
        Source Produced Citation Abbreviation: Image 20
      Process Step:
        Process Description: Perform QA/QC geometric and vertical accuracy check
        Source Used Citation Abbreviation: Image 20
        Source Produced Citation Abbreviation: Image 21
      Process Step:
        Process Description: Perform radiometric QA/QC
        Source Used Citation Abbreviation: Image 21
        Source Produced Citation Abbreviation: Image 22
      Process Step:
        Process Description: Ship DO data to County of Fairfax
        Source Used Citation Abbreviation: Image 22
        Source Produced Citation Abbreviation: Image 23
      Process Step:
        Process Description: County of Fairfax QA/QC procedures
        Source Used Citation Abbreviation: Image 23
        Source Produced Citation Abbreviation: Image 24
    Cloud Cover: 0

Spatial Data Organization Information

Section Index

    Indirect Spatial Reference: 2001 Digital Orthophotography
    Direct Spatial Reference Method: Raster
    Raster Object Information:
      Raster Object Type: Pixel

Spatial Reference Information

Section Index

    Horizontal Coordinate System Definition:
      Planar:
        Map Projection:
          Map Projection Name: Albers Conical Equal Area
        Planar Coordinate Information:
          Planar Coordinate Encoding Method: Coordinate Pair
          Coordinate Representation:
            Abscissa Resolution: 0.01
            Ordinate Resolution: 0.01
      Geodetic Model:
        Horizontal Datum Name: North American Datum of 1983
        Ellipsoid Name: Geodetic Reference System 80
        Semi-major Axis: 6378206
        Denominator of Flattening Ratio: 294.9786982
    Vertical Coordinate System Definition:
      Altitude System Definition:
        Altitude Datum Name: National Geodetic Vertical Datum of 1929
        Altitude Distance Units: feet
        Altitude Encoding Method: Attribute values

Distribution Information

Section Index

    Distributor:
      Contact Information:
        Contact Organization Primary:
          Contact Organization: Fairfax County GIS and Mapping Services
        Contact Position: Database Administrator
        Contact Address:
          Address Type: mailing and physical address
          Address: 12000 Government Center Pw. Suite 117
          City: Fairfax
          State or Province: VA
          Postal Code: 22035
          Country: USA
        Contact Voice Telephone: (703)-324-2712
        Contact TDD/TTY Telephone: 711
        Contact Facsimile Telephone: (703)-324-3937
        Contact Electronic Mail Address: gis.helpq@fairfaxcounty.gov
        Hours of Service: Monday 8:00am - 4:15pm / Tuesday 9:00am - 4:15pm / Wednesday - Friday 8:00am - 4:15pm (EST)

Metadata Reference Information

Section Index

    Metadata Date: 6/30/2004
    Metadata Review Date: 7/14/2004
    Metadata Future Review Date: 1/1/2005
    Metadata Contact:
      Contact Information:
        Contact Organization Primary:
          Contact Organization: Fairfax County GIS and Mapping Services
        Contact Position: Database Administrator
        Contact Address:
          Address Type: mailing and physical address
          Address: 12000 Government Center Pw. Suite 117
          City: Fairfax
          State or Province: VA
          Postal Code: 22035
          Country: USA
        Contact Voice Telephone: (703)-324-2712
        Contact TDD/TTY Telephone: 711
        Contact Facsimile Telephone: (703)-324-3937
        Contact Electronic Mail Address: gis.helpq@fairfaxcounty.gov
        Hours of Service: Monday 8:00am - 4:15pm / Tuesday 9:00am - 4:15pm / Wednesday - Friday 8:00am - 4:15pm (EST)
    Metadata Standard Name: FGDC Content Standards for Digital Geospatial Metadata
    Metadata Standard Version: FGDC-STD-06-1994
    Metadata Time Convention: local time
SMMS Metadata report generated 7/14/2004