2006 Fulton County Georgia Lidar

The Light Detection and Ranging (LiDAR) LAS dataset is a survey of Fulton County. The Fulton County LiDAR Survey project area consists of approximately 690.5 square miles. The LiDAR point cloud was flown at a density sufficient to support a maximum final post spacing of 5 meters for unobscured areas. 3001 Inc. acquired 75 flightlines between March 3, 2006 and March 6, 2006 and 120 flightlines were reflown between July 29, 2006 and August 4, 2006. The data was divided into 5000' by 5000' foot cells that serve as the tiling scheme. The Fulton County LiDAR Survey was collected under the guidance of a Professional Mapper/Surveyor.

Original contact information:

Contact Org: Ayres Associates

Phone: 608-443-1200

The Fulton County LiDAR Survey data will support the creation of Federal Emergency Management Agency Flood Insurance Rate Maps (FEMA FIRM) and an integrated ground and surface water model. The Fulton County LiDAR Survey was collected under the guidance of a Licensed and Professional Surveyor/Mapper.

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The metadata are not complete if the format is not compatible with ArcGIS 9, if it is not FDGC Compliant, and if copies of the survey report in PDF format are not delivered as an attachment. The information in this report are the result of the LiDAR surveys performed on the dates indicated and the general conditions at the time.

A footprint of this data may be viewed in Google Earth at:

https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/2526/supplemental/ga2006_fultoncounty.KMZ

A LiDAR Report from the vendor for this data set may be viewed here:

https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/2526/supplemental/FultonCountyGA_QAreport.pdf

Any conclusions drawn from the analysis of this information are not the responsibility

of the Fulton County Public Works Department, Ayres Associates, USGS, NOAA, the Office for Coastal Management or its partners.

This data can be obtained on-line at the following URL: https://coast.noaa.gov/dataviewer

The data set is dynamically generated based on user-specified parameters.

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None

These unaltered data may not be redistributed without all of the elements of the metadata listed

in the Supplemental Information section of this metadata document. Acknowledgement of Ayres

Associates would be appreciated in products derived from these data.

Stream shore lines and 3-D coordinate line strings were collected as breaklines using LiDAR that was acquired and processed to FEMA specifications. These breaklines were created from on-screen digitizing using a combination of the LiDAR points and the orthophotography. Attributes were verified using routines that verify the vertical and horizontal positions of the breaklines.

All ground control processing and adjustments are performed using published coordinate horizontal and vertical datums (e.g. NGS CORS). For deliverables, Corpscon for Windows Version 5.11.08 (geoid 99) has been used for horizontal and vertical datum conversion as well as for coordinate system conversion purposes (e.g. UTM to State Plane).; Quantitative Value: 3.3 meters, Test that produced the value: This value is computed by comparing ground control to an intensity based image derived from the classified LiDAR data and represents the RMSE of residuals on controls within the project area.

The accuracy assessment was performed using a standard method to compute the root mean square error (RMSE) based on a comparison of ground control points (GCP) and filtered LiDAR data points. Filtered LiDAR data has had vegetation and cultural features removed and by analysis represents bare earth elevations. Testing was performed prior to gridding of the filtered LiDAR data points and construction of the Intergraph .dtm file format. The RMSE figure was used to compute the vertical National Standard for Spatial Data Accuracy (NSSDA). Ground control was established by 3001, Inc. A spatial proximity analysis was used to select edited LiDAR data points contiguous to the relevant GCPs. A search radius decision rule is applied with consideration of terrain complexity, cumulative error and adequate sample size. Cumulative error results from the errors inherent in the various sources of horizontal measurement. These sources include the airborne GPS, GCPs and the uncertainty of the accuracy of the LiDAR data points. This accuracy is achieved prior to the sub-sampling that occurs through integration with the inertial measurement unit (IMU) positions that are recorded. It is unclear at this time whether the initial accuracy is maintained. The horizontal accuracy of the GCPs is estimated to be in the range of approximately 1 to 1.6 inches. Finally, sample size was considered. The specification for the National Standard for Spatial Data Accuracy is a minimum of 20 points to conduct a statistically significant accuracy evaluation (Minnesota Planning, 1999, Positional Accuracy Handbook, Minnesota Planning Land Management Information Center, St. Paul, Minnesota., p.3). Most statistical texts indicate that a minimum of 30 sample points provide a reasonable Approximation of a normal distribution. The intent of the NSSDA is to reflect the geographic area of interest and the distribution of error in the data set (Federal Geographic Data Committee, 1998, Geospatial National Standard for Spatial Data Accuracy, Federal Geographic Data Committee Secretariat, Reston, Virginia, p.3-4). Additional steps were taken to ensure the vertical accuracy Of the LiDAR data including: Step 1: Precision Bore sighting (Check Edge-matching) Step 2: Compare the LiDAR data to the Field Survey (Field survey is to FEMA specifications and more stringent internal specifications) Step 3: Automated Filtering Step 4: Manual Editing (Quality Control) Step 5: 3-D digitizing and Photogrammetric Compilation of hydrographic breaklines.; Quantitative Value: 0.0579 meters, Test that produced the value: This value is computed by comparing ground control elevation to the classified LiDAR ground surface and represents the RMSE of residuals on controls within the project area.

The LAS files were flown at a density sufficient to support a maximum final post spacing of 5 meters for unobscured areas. The bare-earth surface will contain voids in areas that were densely vegetated, covered by bridges, buildings, water, fresh asphalt, sand etc.

The LAS files were flown at a density sufficient to support a maximum final post spacing of 5 meters for unobscured areas. 3001 Inc. acquired 75 flightlines between March 3, 2006 and March 6, 2006 and 120 flightlines were reflown between July 29, 2006 and August 4, 2006. The data was divided into 5000' by 5000' foot cells that serve as the tiling scheme. The Fulton County LiDAR Survey was collected under the guidance of a Professional Mapper/Surveyor.