Data Management Plan

St. Johns County, Florida (County) has developed a comprehensive countywide base mapping and GIS enhancements to support master drainage planning, transportation planning, and preliminary engineering and wetland preservation studies. As part of this effort, Woolpert was contracted by Jones, Edmunds & Associates (JEA) to develop the new imagery and new DTM. The project consists of new 6-inch 4-Band Orthoimagery, new 1-meter max LiDAR, new 1-foot contours, updating of topographic/planimetric features. This data set is one component of a digital terrain model (DTM) for St. Johns County. The dataset is comprised of mass points, 2-D and 3-D breakline features, 1-foot and 2-foot contours, ground control, vertical test points, and a footprint of the data set, in the ESRI ArcGIS File Geodatabase format. In accordance with the counties specifications, the following breakline features are contained within the database: closed water bodies (lakes, reservoirs, etc) as 3-D polygons; linear hydrographic features (streams, shorelines, canals, swales, embankments, etc) as 3-D breaklines; coastal shorelines as 3-D linear features; edge of pavement road features as 3-D breaklines; soft features (ridges, valleys, etc.) as 3-D breaklines; island features as 3-D polygons; concretedam, culvert, footprint, lowconfidence, lowconfidenceanno, overpass, pipe, roadcenterlineoverbridge and swamppoint as 2-D features. Contours were generated from LiDAR ground class and breaklines and meet National Map Accuracy Standards. The LiDAR masspoints are delivered in the LAS file format based on the Florida statewide 5,000' by 5,000' grid. The GEOID model used to reduce satellite derived elevations to orthometric height is GEOID12A. Breakline features were captured to develop a hydrologically correct DTM. The coastalshoreline has a constant value of -0.6’ that was statistically derived from the LiDAR point cloud collected within the 2-hour window of MLL tide. 2008 Hydrographic and soft features were used to supplement the 2013 breaklines in Low Confidence areas.

The NOAA Office for Coastal Management (OCM) received the 5ft DEM data from St. Johns County GIS in March 2018 and processed the data to be available for download from the Data Access Viewer (DAV) and via https.

In addition to these bare earth Digital Elevation Model (DEM) data, the lidar point data that these DEM data were created from, are also available. These data are available for custom download at the link provided in the URL section of this metadata record.

Planimetric and breakline data are also available. These data are available for download at the link provided in the URL section of this metadata record. Please note that these products have not been reviewed by the NOAA Office for Coastal Management (OCM) and any conclusions drawn from the analysis of this information are not the responsibility of NOAA or OCM.

Process Steps:

• Airborne terrestrial LiDAR was collected for St. Johns County, FL. The LiDAR system acquisition parameters were developed based on a maximum average ground sample distance of 3.23 feet. A Leica ALS70 LiDAR sensor was used for acquisition. Acquisition specifications for the sensor were as follows: Field of View (full angle) - 40 degrees, Nominal flight altitude (AGL) - 6500 feet, Airspeed - 172 mph (150 knots), Laser pulse rate - 270,000 Hz, Nominal swath width (on ground) - 4732 feet, Maximum cross track point spacing - 2.98 feet, Maximum along track point spacing - 3.01 feet, Average point spacing - 3.28 feet, Flight line spacing - 3314 feet, Side overlap - 29.3 percent. Prior to the LiDAR acquisition, the system underwent a system calibration to verify the operational accuracy and misalignment angles. LiDAR data acquisition only occurred when the sky was sufficiently clear of clouds, smoke, and atmospheric haze. The LiDAR data was processed immediately following the acquisition to verify the coverage had no voids. The GPS and IMU data was post processed using differential and kalman filter algorithms to derive a smoothed best estimate of trajectory. The quality of the solution was verified to be consistent with the accuracy requirements of the project. The ground control system to support the LiDAR survey consisted of 24 control points surveyed specifically for this project. The LiDAR data was post processed and verified to be consistent with the project requirements in terms of post spacing and absence of artifacts. The point cloud underwent classification to determine bare-earth points (class 2), low vegetation points (class 3), medium vegetation points (class 4), high vegetation points (class 5), building points (class 6) noise points (class 7), water returns (class 9), breakline proximity points (class 10), bridge points (class 13, canopy/covered walkway points (class 14) and unclassified data (class 1).
• Once the initial lidar point cloud was derived, Woolpert performed QC to look for any systematic error within the lidar flights using proprietary software. Any systematic error was identified and removed, the individual lidar flights were clipped to remove overlap between the adjacent flights lines and to provide a homogeneous coverage over the project extents. Using the homogeneous coverage, above ground features were classified and removed using proprietary software to produce the bare-earth coverage.
• Hard and soft breakline features were compiled as 2D and 3D features in the softcopy environment using DATEM’s Summit Evolution Capture software on an Intel® Core™ i7 – 3770 CPU @ 3.40GHz photogrammetric workstation. DATEM, Inc. of Anchorage, Alaska distributes the Summit software. The DTM was delivered as lidar mass points in LAS version 1.2 and the breaklines were delivered in an ArcGIS File Geodatabase.
• 2019-03-26 00:00:00 - The NOAA Office for Coastal Management (OCM) received 1 ESRI grid file from the St. Johns County, Florida GIS Department. The data were in Florida State Plane East NAD83 (HARN) coordinates (US survey feet) and NAVD88 (Geoid12A) elevations in US survey feet. This information, however, was not present in the file georeferencing information. The bare earth raster file was at a 5 ft grid spacing. OCM performed the following processing on the data for Digital Coast storage and provisioning purposes: 1. Used gdal_translate to add the projection and vertical georeferencing (EPSG codes 2881 and 6360) information to the files. 2. Used gdal_translate to convert the file from ESRI grid format to geotiff format. 3. Copied the files to https

Data is available online for bulk and custom downloads.