20211122 14090600 1.0 FGDC CSDGM Metadata FALSE DCOCTO-2021.sid 389400.000000 408600.000000 124200.000000 148200.000000 1 002 Projected GCS_North_American_1983 Linear Unit: Meter (1.000000) NAD_1983_StatePlane_Maryland_FIPS_1900 <ProjectedCoordinateSystem xsi:type='typens:ProjectedCoordinateSystem' xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance' xmlns:xs='http://www.w3.org/2001/XMLSchema' xmlns:typens='http://www.esri.com/schemas/ArcGIS/10.8'><WKT>PROJCS[&quot;NAD_1983_StatePlane_Maryland_FIPS_1900&quot;,GEOGCS[&quot;GCS_North_American_1983&quot;,DATUM[&quot;D_North_American_1983&quot;,SPHEROID[&quot;GRS_1980&quot;,6378137.0,298.257222101]],PRIMEM[&quot;Greenwich&quot;,0.0],UNIT[&quot;Degree&quot;,0.0174532925199433]],PROJECTION[&quot;Lambert_Conformal_Conic&quot;],PARAMETER[&quot;False_Easting&quot;,400000.0],PARAMETER[&quot;False_Northing&quot;,0.0],PARAMETER[&quot;Central_Meridian&quot;,-77.0],PARAMETER[&quot;Standard_Parallel_1&quot;,38.3],PARAMETER[&quot;Standard_Parallel_2&quot;,39.45],PARAMETER[&quot;Latitude_Of_Origin&quot;,37.66666666666666],UNIT[&quot;Meter&quot;,1.0],AUTHORITY[&quot;EPSG&quot;,26985]]</WKT><XOrigin>-36747100</XOrigin><YOrigin>-29091500</YOrigin><XYScale>121236910.21292362</XYScale><ZOrigin>-100000</ZOrigin><ZScale>10000</ZScale><MOrigin>-100000</MOrigin><MScale>10000</MScale><XYTolerance>0.001</XYTolerance><ZTolerance>0.001</ZTolerance><MTolerance>0.001</MTolerance><HighPrecision>true</HighPrecision><WKID>26985</WKID><LatestWKID>26985</LatestWKID></ProjectedCoordinateSystem> 8 FALSE Wavelet (MG4) 5 MrSID TRUE continuous unsigned integer 20211201 14381900 20211201 14415000 5000 150000000 FGDC dataset GIS Data Coordinator D.C. Office of the Chief Technology Officer GIS Data Coordinator 200 I Street SE, 5th Floor Washington DC 20003 dcgis@dc.gov (202) 727-2277 (202) 727-5660 8:30 am - 5:00 pm GIS Data Coordinator Raster Dataset GIS Data Coordinator D.C. Office of the Chief Technology Officer GIS Data Coordinator 200 I Street SE, 5th Floor Washington DC 20003 dcgis@dc.gov (202) 727-2277 (202) 727-5660 8:30 am - 5:00 pm GIS Data Coordinator DC datasets can be downloaded from "https://opendata.dc.gov". SID Aerial Photography (Orthophoto SID) - 2021 2021-03-11T00:00:00 2021-11-01T00:00:00 remote-sensing image GIS Data Coordinator D.C. Office of the Chief Technology Officer GIS Data Coordinator 200 I Street SE, 5th Floor Washington DC 20003 dcgis@dc.gov (202) 727-2277 (202) 727-5660 8:30 am - 5:00 pm GIS Data Coordinator <DIV STYLE="text-align:Left;"><DIV><DIV><P><SPAN>2021 Orthophoto - 3 inch resolution: This document describes the processes used to create the orthoimagery data produced for the District of Columbia from 2021 digital aerial photography. It was flown on March 11, 2021. </SPAN><SPAN>The aerial imagery acquisition was flown to support the creation of 4-band digital orthophotography with a 3 inch/0.08 meter pixel resolution over the full project area covering the District of Columbia which is approximately 69 square miles. The contractor received waivers to fly in the Flight Restricted Zone (FRZ) and P-56 areas. The ortho imagery was submitted to DC OCTO in GeoTiff/TFW format tiles following the tile scheme provided by OCTO. MrSID and JPEG2000 compressed mosaics were delivered as well using a 50:1 compression ratio.</SPAN></P></DIV></DIV></DIV> Aerial Photography Download SID file (Orthophoto) of Washington, DC at 3 inch resolution. Dated 2021. https://dcgis.dc.gov Version 6.2 (Build 9200) ; Esri ArcGIS 10.8.1.14362 orthophoto ortho aerial imagery DC DC GIS basemap 2021 aerial aerial photography planimetrics District of Columbia Washington orthophotography imageryBaseMapsEarthCover 2021 image picture orthophotography planning imagery orthos aerial photography imageryBaseMapsEarthCover Geographic Names Information System GIS Data Coordinator D.C. Office of the Chief Technology Officer GIS Data Coordinator 200 I Street SE, 5th Floor Washington DC 20003 dcgis@dc.gov (202) 727-2277 (202) 727-5660 8:30 am - 5:00 pm GIS Data Coordinator Washington D.C. District of Columbia United States of America (USA) -77.13306855102523 -76.91711853881849 38.80635431408878 38.97390470184547 1 -77.122373 -76.900716 38.785481 39.001746 GIS Data Coordinator D.C. Office of the Chief Technology Officer GIS Data Coordinator 200 I Street SE, 5th Floor Washington DC 20003 dcgis@dc.gov (202) 727-2277 (202) 727-5660 8:30 am - 5:00 pm GIS Data Coordinator <DIV STYLE="text-align:Left;"><DIV><DIV><P><SPAN>This work is licensed under a </SPAN><A href="https://creativecommons.org:443/licenses/by/4.0/"><SPAN>Creative Commons Attribution 4.0 International License</SPAN></A><SPAN>.</SPAN></P></DIV></DIV></DIV> GIS Data Coordinator D.C. Office of the Chief Technology Officer GIS Data Coordinator 200 I Street SE, 5th Floor Washington DC 20003 dcgis@dc.gov (202) 727-2277 (202) 727-5660 8:30 am - 5:00 pm GIS Data Coordinator 1 -77.122373 -76.900716 39.001746 38.785481 GIS Data Coordinator D.C. Office of the Chief Technology Officer GIS Data Coordinator 200 I Street SE, 5th Floor Washington DC 20003 dcgis@dc.gov (202) 727-2277 (202) 727-5660 8:30 am - 5:00 pm GIS Data Coordinator Quality control procedures were implemented and documented at each step of the project to ensure that all services required by the contract are completed to specification; they include visual (manual) inspections, automated routines, and technical reviews. Aerial Data Acquisition QA/QC: 1. Flight Planning - The flight plan was based on the scope of work (SOW), DC OCTO provided boundary, and flight restrictions. 2. Ground GPS Acquisition - The GPS equipment was assembled on a monument or a temporary established point and data was recorded. The data was then checked to ensure the PDOP is less than 3.0. 3. Data Acquisition Prior to full flight, the following steps was performed: - Inspect storage and system components to ensure all units are operational and there is sufficient storage space - Select and confirm the lever arm coordinates - Load navigation system and perform system check - Perform 5 minute static alignment and record PDOP, GPS, and UTC start time - Ensure IMU is operational - Ensure all channels are operational, as applicable. After the pre-flight checks, the crew began flight line data recording: observe video display, POS status and mass memory screens; record UTC start/stop times, GPS data, ground speed, altitude, comments/concerns, lines, waypoints and times on the flight log. When the flight mission was completed, a 5 minute static alignment was performed followed by a systematic shutdown of the system. All collected data was downloaded for QC. Ground Control QA/QC: The Ground Control QA/QC strategy is based on reviewing the criteria described below: - Incidences of High PDOP - Poor network closure - Inadequate point location - Missing or omitted points - Damaged or missing panels The evaluation of the ground control is done through the following steps: - All planning, reconnaissance, field observations, post-processing, adjustments, and final report development will be performed under the direct supervision of a highly-experienced land surveyor. - Fixed height tripods will be used during the GPS survey to eliminate antenna height measurement error. - The field crews will perform processing and closure analysis of the data to eliminate field blunders and determine baselines, which do not fit the network or project tolerances and must be re-observed. - The final adjustment and processing of target locations will be coordinated, directed and completed by a single surveyor to ensure the overall consistency and integrity of the control network required to accurately map an area of this size. These efforts will also facilitate a smoother aerial triangulation process. IMU/GPS Processing QA/QC: Airborne GPS control is accomplished through the simultaneous observation of five or more satellites in the GPS constellation using the on-board receiver and one or more ground receivers (base stations) located over known control points that are in the vicinity of the project area. If accessible to non-airport personnel, the GPS occupation of a primary airport control station (PACS) is established prior to any airborne GPS collection. A GPS receiver is placed on a temporary marker using PK nails to define the location. The GPS station records at a one second interval for the duration of the airborne collection. Coordinates for this base station point is adjusted by the project surveyor and is tied into the project control network. Airborne GPS and IMU data is immediately processed using the airport GPS base station data. When necessary, combination of CORS stations and surveyor established GPS stations are used to ensure that a base station is operating within range of the aircraft at all times. If this occurs, it is included in the pre-planning. Once a decision has been made to fly, any GPS stations established for the project area is activated at a one second interval for the duration of the airborne collection. Aerotriangulation QA/QC: The Aerotriangulation QA/QC strategy is based on the criteria described in the table below: - Missing or corrupt ground control information - Camera calibration - GPS and IMU data integrity An initial bundle/block adjustment is developed for each data sortie. The accuracy of each bundle/block is confirmed through an RMSE evaluation against the project ground control. The accuracy is verified through an iterative process where the adjustment is repeatedly run, while progressively increasing the constraints on the ground control. After the accuracy is verified, the technician applies the bundle adjustment result to the images of each AT block (consisting of multiple lifts or sorties). The results of the adjustment are verified through the generation of the full-resolution panchromatic orthophoto chips over the ground control points for the data sortie. The orthophoto chips are inspected by the photogrammetric technician to identify any errors in the adjustment to ensure the accuracy meets project specification. The technician also generates and visually reviews that orthophoto strips cover across all flight lines to ensure edge matching between flight lines. The adjustment/inspection process is repeated as bundle/block adjustment for adjoining sorties are complete and these small blocks are adjusted to build the overall bundle adjustment. Throughout the process, the accuracy of each adjustment is checked against the GPS ground control points. Imagery and Orthophoto QA/QC: The Orthophoto Rectification QA/QC strategy is based on the criteria described below: - Edge matching - Fit to ground control - Radiometric consistency - Insufficient coverage - Correct color band rendition Preliminary field data is reviewed to ensure that there are no gaps between flight lines before the flight crew leaves the project site. Data will be inspected for turbulence, and if it is present and affects the data quality, the line is rejected. A full visual review is conducted in the office to ensure that it is complete, uncorrupted, and that the entire project area has been covered without gaps between flight lines. The technician performs visual inspection of raw images on selected bands of each collected flight lines for completeness, this step also ensures proper sensor function of the sensor. The flight line trajectory files are reviewed to ensure completeness of acquisition for project flight lines, calibration lines, and cross flight lines. The raw RGB images for each collected flight lines are rectified using the DEM data and the GPS/IMU solution in Fugro proprietary software. The technician visually reviews all rectified images to ensure completeness of acquisition for all flight lines. The technician also uses these images to identify any gaps, clouds, shadows and any un-predicted issues in project area. The orthophoto production process incorporates the ability to develop a completed digital orthophoto mosaic of all or part of a data sortie at a greatly reduced resolution. “Quick look” generation permits the quick assessment of iterative adjustments to finalize the parameters that are applied to the data for radiometric corrections to the orthophoto while data limiting computer resources by only processing the imagery at full resolution once. Quick looks also enable the technician to assess the accuracy of the processed imagery as well as identifying areas of distortion that would necessitate regeneration of the DEM or aerotriangulation data. The imagery is visually checked for accuracy on the workstation screen, and its absolute accuracy is verified by overlaying and comparing the locations of the control that are visible on the image against a CAD file containing the point locations in vector form. The edge matching of adjacent strips of imagery is accomplished using a single color band from adjoining strips of imagery displaying each strip in alternating colors of red and cyan. In areas where the overlapping images are coincident, the imagery appears in a gray scale rendition while any offset is colored red or cyan. Any offsets are measured to confirm that the offset falls within the accuracy specification for the project. Using the parameters developed from the quick look, the finishing department radiometrically corrects the orthophotos prior to completing the mosaicking and clipping of the final tiles, then the files are returned to digital orthophoto production for mosaicking. The finishing department performs a 100% final visual check for orthophoto image quality prior to outputting the approach data to the designated media. True Orthophotography: Areas designated for true ortho capture photo capture are planned with a minimum 80 percent "endlap" between frames and 80 percent "sidelap" between flight lines. PCI Geomatics GXL and Focus tools are used in conjunction with internal proprietary techniques, and solutions to offer a comprehensive True Ortho product. The process utilizes a DSM extracted at the same resolution of the imagery to generate orthorectified imagery. With this approach, True Orthos are generated without voids, and the buildings are displayed without lean. The workflow is executed to produce the final products: • DSM Extraction • DSM Orthorectification • Mosaic Prep/Generation • Post Mosaic Editing GXL’s DEM Extraction workflow automatically scans an input directory for all valid stereo pairs, computes the epipolarized images and extracts the Digital Surface Model (DSM) for each stereo pair. Elevation values in a DSM are determined by matching points in a left and right epipolar input image using image correlation. After all DSMs in the batch are extracted, the GXL automatically merges them together to create a seamless multiview DSM. A “Pattern Suppression” algorithm helps to reduce or eliminate blunders in the output digital surface model, The DSM Orthorectification operation orthorectifies the aerial imagery using the derived DSM. Occlusion zones that are created during the ortho process are detected for each ortho image and filled by retrieving optimal visible pixels from the adjacent overlapping ortho images. A Mosaic Preparation processing module automatically normalizes the images, calculating color balancing and generating the seamlines (cutlines). Building footprints are used as a “cutline mask” forcing the mosaicker to avoid buildings, eliminating an extreme majority of known buildings. A Mosaic tool is used to adjust cutlines and perform color balancing. PCI Geomatica and internal proprietary tools and techniques, are used to conduct a comprehensive QA/QC while simultaneously editing the imagery for DSM, seamline, or mosaicking errors. Acquisition The aerial imagery acquisition for DC OCTO was flown to support the creation of 4-band digital orthophotography with 8 cm pixel resolution over the full project area covering the District of Columbia. Due to the security requirements in the area, waivers were needed to fly in the Flight Restricted Zone (FRZ) and P-56 areas. The aerial photographic mission was completed by Keystone Aerial Surveys and was composed of two flight areas: DCM3 Red Area (25 flight lines) and DCM3 Blue Area (114 flight lines) at an average altitude of 4,000 feet above mean sea level. Data was collected on March 11, 2021 in one lift. All data were collected with censor type DCM III, serial sensor 545. Aerial photography was collected in conjunction with airborne GPS. Ground Control and Aerotriangulation Rice Associates, under contract to Fugro Geospatial, Inc. successfully established ground control for the DC OCTO project area. Ground control for the DC OCTO project area consisted of a total of 25 points: six new ground control points and 19 previously collected ground control points collected by Wiles Mensch Corporation in 2017 and Rice Associates in 2019. GPS was used to establish the control network. The horizontal datum is provided in NAD83/HARN91. The vertical datum was the North American Vertical Datum of 1988 (NAVD88) using GEOID12B. Catalyst Ortho Engine software was used for downloading and preparing imagery collected with the DCM III Sensor for softcopy photogrammetric use. The data was differentially processed against a base station. After the differential GPS solution was checked and verified, the software computed an integrated GPS/IMU navigation solution. The GPS/IMU trajectory was computed to a full x, y, z, omega, phi, kappa exterior orientation of each scan line. A fully automatic aerotriangulation process was performed to minimize the residual errors in the GPS/IMU derived exterior orientations. The aerotriangulation also allowed the introduction of ground control and checkpoints to ensure the accuracy specifications were achieved. Stereo imagery (level 1 georeferenced imagery) was created by applying the aerotriangulation solution to the raw imagery. This resampling removes aircraft motion and provides epipolar geometry imagery for stereo viewing. Low resolution images were created to determine the radiometric correction for each lift of imagery. Those settings were then used to create full resolution imagery strips. Processing Ground Orthoimagery Upon the completion of the Aerotriangulation, a DEM was generated for the rectification of the imagery. The ortho-rectified strips (each flight line) were mosaicked together using proprietary image database and mosaicking software. The database was edited using Photoshop and QA/QC'ed for coverage, seam lines, smears, and other artefacts. The imagery was clipped out of the database into the sheet layout generated based on OCTO requirements. In the clipping stage, the coordinate system and georeferencing was embedded into the header of the files. True Orthoimagery GXL is a server-side high volume geospatial image-processing system designed to leverage modern computing technology, and Geomatica is PCI’s visualization and analytical desktop platform. GXL was utilized for generating the DSM Ortho products, and Geomatica was used for Quality Assurance (QA) purposes. The workflow was executed to produce the final products: • DSM Extraction • DSM Orthorectification • Mosaic Prep/Generation • Post Mosaic Editing GXL’s DEM Extraction workflow automatically scans an input directory for all valid stereo pairs, computes the epipolarized images and extracts the Digital Surface Model (DSM) for each stereo pair. Elevation values in a DSM are determined by matching points in a left and right epipolar input image using image correlation. The image disparity for the point pair is computed and this value, combined with the geometric model for each image, is used to compute the scene elevation for the corresponding scene point. After all DSMs in the batch are extracted, the GXL automatically merges them together to create a seamless multiview DSM. Using a “Pattern Suppression” algorithm helps to reduce or eliminate blunders in the output digital surface model (DSM). Quality Assurance (QA) was performed on the derived DSM using Geomatica’s DEM Editing toolset. Utilizing the Live Ortho Preview capability, users can generate ortho images on the fly to check the quality of the DEM. Blunders and artifacts can be removed/fixed using Geomatica’s DEM editor. The DSM Orthorectification operation is a straightforward process that orthorectifies the aerial imagery using the derived DSM. Occlusion zones that are created during the ortho process are detected for each ortho image and filled by retrieving optimal visible pixels from the adjacent overlapping ortho images. The Mosaic Preparation processing module is responsible for automatically normalizing the images, calculating color balancing and generating the seamlines (cutlines). The output is a very lightweight mosaic preview that can be viewed and edited using the GXL’s Mosaic Tool. The Mosaic Preview does not generate an actual mosaic image, but rather it stores all the necessary information for future full resolution mosaics. Fugro used DC OCTO’s collected building footprints as a “cutline mask” forcing the mosaicker to avoid buildings eliminating an extreme majority of known buildings. Mosaic editing was conducted in the Mosaic tool to adjust cutlines and perform color balancing. Deliverables The ortho imagery was submitted to DC OCTO in GeoTiff/TFW format tiles following the tile scheme provided by OCTO. 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