The District of Columbia

Ortho - 2005

Ortho - 2005

by Office of the Chief Technology Officer on 04/04/2005

Keywords
About: Planimetric, Aerial Photography, Planning, Imagery, Orthos, Orthophotography, imageryBaseMapsEarthCover
Taking place at: United States of America (USA), Washington, D.C., District of Columbia, D.C.

Abstract

2005 Orthophoto - This document describes the processes used to update the planimetric and topographic data originally produced for the District of Columbia from the 2005 aerial photography.

The project area covers the entire District of Columbia which is approximately 69 square miles. The digital imagery was used to create natural color digital orthophotography with 15cm pixel resolution. The final orthophotography deliverable products for this project consist of 328 ortho tiles at a scale of 1 to 2400. The tile dimensions are 800 meters by 800 meters. A corresponding MrSid image was created by mosaicking the 328 ortho tiles together and compressing the image using an 80 to 1 compression ration.

All DC GIS data is stored and exported in Maryland State Plane coordinates NAD 83 meters.

METADATA CONTENT IS IN PROCESS OF VALIDATION AND SUBJECT TO CHANGE.

Purpose

This data is used for the planning and management of Washington, D.C. by local government agencies.

Access constraints

Contact OCTO GIS. Any data obtained outside of OCTO GIS are unauthorized copies.

Use constraints

Acknowledgment of the DC Geographic Information Systems Program (DC GIS). The District of Columbia Government makes no claims as to the completeness, accuracy or content of any data contained hereon, and makes no representation of any kind, including, but not limited to, the warranty of the accuracy or fitness for a particular use, nor are any such warranties to be implied or inferred with respect to the information or data furnished herein.

Point of contact


in D.C. Office of the Chief Technology Officer

441 4th St NW, Suite 930 South
Washington D.C., 20001,

fax: (202)727-5660
hours: 8:30 AM - 5:00 PM

Credits


D.C. Office of the Chief of Technology Officer (OCTO)
EarthData International, Inc
7320 Executive Way
Frederick, MD 21704
(301)948-8550

Data accuracy

Accuracy
N/A

Logical consistency
Compliance with the accuracy standard was ensured by the placement of photo identifiable ground control points and the collection of airborne GPS data. The elevation data were generated by autocorrelation and manual processes. An RMSE value for each tile was calculated based on the photos utilized in the production of the tile by comparing the AT X and Y coordinates. This value represents an estimate of the accuracy of the horizontal coordinate measurements in the tile expressed in meters.

Completeness
Compliance with the accuracy standard was ensured by the placement of photo identifiable ground control points
and the collection of airborne GPS data.

Horizontal positional accuracy
The horizontal accuracy of the orthorectified images is mainly determined by the accuracy of the aerotriangulation and digital surface model (DSM). For each rectified image, an RMSE value for all of the standard errors of the tie/pass/control points located in that image and computed by the aerotriangulation solution was calculated. The DSM accuracy assessment was achieved by comparing the aerotriangulation-derived elevation with the elevation of the DSM. In addition, visual examination was employed to assess all tiles and its relative edge match. All results were examined for consistency and its compliance with the ASPRS Standards for Large Scale Mapping at 1 to 1200 which states that the orthos will meet 1 foot RMSE at the 95% confidence clevel.

Vertical positional accuracy
N/A

Lineage / Sources

  • Aerial Photography of Washington, D.C.
    filmstrip, This aerial photography was composed of 24 flight lines and a total of 1023 exposures. Imagery was obtained at an altitude of 1,100 meters above mean terrain (AMT) 7200. The mission was flown with two Wild RC30 cameras serial no. 5368 with 153.743 mm lens serial number 13413 and serial no. 5324 with 153.247 mm lens serial number 13365 with ABGPS.
    Aerial Photography
    by EarthData International, Inc, 20060630
  • Report of Survey Washington, DC Area
    electronic mail system, TerraSurv established 30 photo identification control points to support the aerotriangulation process. Continuously Operating Reference Station (CORS) station USNO (PIDAI7403) was used as the control for this project. The horizontal datum was the North American Datum of 1983, CORS adjustment (NAD 1983 CORS). The vertical datum was the North American Vertical Datum of 1988 (NAVD 1988).
    GPS ground control
    by TerraSurv, Inc, 20060630
Lineage / Processes

in EarthData International, Inc

7320 Executive Way
Frederick MD, 21704,

phone: (301)948-8550
fax: (301)963-2064
hours: 8:30 Am - 5:00 PM Mon - Fri
Source photography - Wild RC-30 camera, natural color stable base.
Control - airborne GPS supplemented with photo identifiable field control.
Scanning - Z/I Imaging PhotoScan flatbed metric scanner.
Aerotriangulation - Photo-T.
Elevation Model - Lidar, autocorrelation and manual collection and update.
Radiometric Balancing - Proprietary and COTS Software (PhotoShop).
Orthorectification - Z/I Ortho Pro 4.0 software package.
Mosaic - Z/I Ortho Pro 4.0 software package.
Processed on Windows NT/2000 systems.

Analytical Aerotriangulation:

The ground control and airborne GPS data was integrated into a rigid network through the completion of a fully analytical bundle aerotriangulation adjustment.

1. The original aerial film was scanned at a resolution of 21 microns. The scans were produced using Z/I Imaging PhotoScan flatbed metric scanners.
2. The raster scans were given a preliminary visual check on the scanner workstation to ensure that the raster file size is correct and to verify that the tone and contrast were acceptable. A directory tree structure for the project was established on one of the workstations. This project was then accessed by other workstations through the network. The criteria used for establishment of the directory structure and file naming conventions accessed through the network avoids confusion or errors due to inconsistencies in digital data. The project area was defined using the relevant camera information that was obtained from the USGS camera calibration report for the aerial camera and the date of photography. The raster files were rotated to the correct orientation for mensuration on the softcopy workstation. The rotation of the raster files was necessary to accommodate different flight directions from one strip to the next. The technician verified that the datum and units of measurement for the supplied control were consistent with the project requirements.
3. The photogrammetric technician performed an automatic interior orientation for the frames in the project area. The softcopy systems that were used by the technicians have the ability to set up predefined fiducial templates for the aerial camera(s) used for the project. Using the template that was predefined in the interior orientation setup, the software identified and measured the eight fiducial positions for all the frames. Upon completion, the results were reviewed against the tolerance threshold. Any problems that occurred during the automatic interior orientation would cause the software to reject the frame and identify it as a potential problem. The operator then had the option to measure the fiducials manually.
4. The operator launched the point selection routine which automatically selected pass and tie points by an autocorrelation process. The correlation tool that is part of the routine identified the same point of contrast between multiple images in the Von Gruber locations. The interpolation tool can be adjusted by the operator
depending on the type of land cover in the triangulation block. Factors that influence the settings include the amount of contrast and the sharpness of features present on the photography. A preliminary adjustment was run to identify pass points that had high residuals. This process was accomplished for each flight line or partial flight line to ensure that the network has sufficient levels of accuracy. The points were visited and the cause for any inaccuracy was identified and rectified. This process also identified any gaps where the point selection routine failed to establish a point. The operator interactively set any missing points.
5. The control and pass point measurement data was run through a final adjustment on the Z/I SSK PhotoT workstations. The PhotoT program created a results file with the RMSE results for all points within the block and their relation to one another. The photogrammetrist performing the adjustments used their experience to determine what course of action to take for any point falling outside specifications.
6. The bundle adjustment was run through thePhotoT software several times. The photogrammetrist increased the accuracy parameters for each subsequent iteration so, when the final adjustment was run, the RMSE for the project met the accuracy of 1 part in 10,000 of the flying height for the horizontal position (X and Y) and 1 part in 9,000 or better of the flying height in elevation (Z). The errors were expressed as a natural ratio of the flying height utilizing a one-sigma (95%) confidence level.
7. The accuracy of the final solution was verified by running the final adjustment, placing no constraints on any quality control points. The RMSE values for these points must fall within the tolerances above for the solution to be acceptable.
8. The final adjustment generates three files. The .txt file has all the results from the adjustment with the RMSE values for each point measured. The .XYZ file contains the adjusted X, Y, Z,coordinates for all the measured points and the .PHT file contains the exterior orientation parameters of each exposure station.

in EarthData International, Inc

7320 Executive Way
Frederick MD, 21704, U.S.

phone: (301)948-8550
fax: (301)963-2064
hours: 8:30 Am - 5:00 PM Mon - Fri
Digital Elevation Model (DEM):

Both Lidar and previously produced DEM data was available to support the production process. Following an analysis of the data the previously produced DEM was selected for update and use.

The following provides a step-by-step outline of the production process.

1. The existing DEM which was comprised of both gridded mass points from 10 to 20 meters with spots, and vertices of contour lines was converted to dgn files for compilation.
2. The DEM was then merged together in MicroStation V8, and then split into 34 tiles, approximately 3077m X 3029m.
3. The compilation team updated the data with breaklines where needed, and collected 3D bridges. 3D bridges were collected to prevent smearing and warping, caused by the elevation difference between the bare earth and the elevated bridges. Proprietary MDLsfor Microstation were run to create a 10 to 15 meter buffer around the bridges and to clip the surrounding ground data.
4. The dgn files were then merged into four large areas for QC purposes. The files were imported into TerraSolid/TerraModler and a tin and a color relief was generated to search for any spikes or mismatches. This check in performed to fix any problems before going to the ortho stage. Large water areas were filled with elevation points.
5. Complex lines, shapes and arcs were dropped before delivering to the ortho epartment. A final level listing was run to ensure all the lines were dropped and the files wereclean. This listing was provided to the ortho team.

in EarthData International, Inc

7320 Executive Way
Frederick MD, 21704, U.S.

phone: (301)948-8550
fax: (301)963-2064
hours: 8:30 Am - 5:00 PM Mon - Fri
Orthophotography:

The digital orthophotography was produced in natural color with a 0.15 meter pixel resolution. A step-by-step breakdown of the digital orthophoto production process follows:

1. A representative number of raster image files were visually checked for image quality on the workstation.
2. The digital image files were oriented on the digital orthophoto production workstation. The following information was then loaded onto the workstation.
- The camera calibration parameters and flight line direction.
- Ground control and pass point locations.
- The exterior orientation parameters from the aerotriangulation process.
- ASCII file containing the corner coordinates of the orthophotos.
- The digital elevation model in a DGN format referenced to Maryland State Plane, NAD83, meters.
- Project-specific requirements such as final sheet size and resolution.
- Orientation parameters developed from the aerotriangulation solution.
3. A coordinate transformation based on the camera calibration fiducial coordinates was then undertaken. This transformation allowed the conversion of every measured element of the plates to a sample/line location. Each pixel in an image was then referenced by sample and line (its horizontal and vertical position) and matched to project control. The newly rectified image was visually checked for pixel drop-out and/or other artifacts that may degrade the final orthophoto image.
4. DEM data was imported and written to the correct subdirectory on disk. The final digital orthophotos were referenced to Maryland State Plane Coordinates system, NAD83, meters.
5. The DEM file was reinspected for missing or erroneous data points.
6. A complete differential rectification was carried out using an exponential algorithm that removed image displacement due to topographic relief, tip and tilt of the aircraft at the moment of exposure, and radial distortion within the camera. Each final orthophoto was produced at a 0.15 meter pixel resolution.
7. Each digital orthophoto image was visually checked for accuracy on the workstation screen. The digital orthophotos were then edge-matched using a module of the Ortho Pro software package.
8. Once the orthophotos were inspected and approved for accuracy, the files were copied to the network and downloaded by the orthophoto finishing department. This production unit was responsible for radiometrically correcting the orthophotos prior to completing the mosaicking and clipping of the final tiles. The final 800 X 800-meter tiles are clipped out and the imagery is output in GeoTIFF format.
9. The processed images were mosaicked using the Ortho Pro software. File names were assigned.
10. The finishing department performed final visual checks for orthophoto image quality. The images were inspected using Adobe Photoshop, which enabled the technician to remove dust and lint from the image files interactively.
11. The final orthophoto images were written out into Arc/Info readable, GeoTIFF format.
12. A corresponding MrSid image was created by mosaicking the 328 ortho tiles together and compressing the image using an 80 to 1 compression ratio.

Distribution

Most DC GIS datasets can be downloaded from "http//dcgis.dc.gov" on the data center page. Orders can also be made by contacting OCTO GIS at "dcgis@dc.gov", especially for datasets not available for download

Distribution liability
Acknowledgment of the DC Geographic Information Systems Program (DC GIS). The District of Columbia Government makes no claims as to the completeness, accuracy or content of any data contained hereon, and makes no representation of any kind, including, but not limited to, the warranty of the accuracy or fitness for a particular use, nor are any such warranties to be implied or inferred with respect to the information or data furnished herein.

Distributed by

in D.C. Office of the Chief Technology

441 4th Street NW Suite 930 South
Washington D.C., 20001, USA

fax: (202)727-5660
hours: 8:30 am - 5:30 pm

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Metadata

FGDC Content Standards for Digital Geospatial Metadata / FGDC-STD-001-1998 as of 06/15/2009

Provided by

in D.C. Office of the Chief Technology

441 4th Street NW Suite 930
Washington D.C., 20001,

phone: N/A
fax: (202)727-5660
hours: 8:30 am - 5:00 pm