2013 South Carolina DNR Lidar DEM: Beaufort County

LIDAR acquisition began on March 6, 2013 (julian day 065) and was completed on April 20, 2013 (julian day 079). A total of 16 survey missions were flown to complete the project.

The flight plan was flown as planned with no modifications. There were no unusual occurrences during the acquisition and the sensor performed within specifications. There were 203 flight lines required to complete the project.

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Information on the NOAA Office for Coastal Management (OCM)

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This graphic displays the footprint for this lidar data set.

Link to data set report.

Link to data set report.

Breaklines may be found at the bulk download page in both ESRI File Geodatabase and Geopackage formats.

Data for the South Carolina Dept of Natural Resources project was acquired by Laser Mapping Specialist, Inc. (LMSI)

The project area included approximately 785 contiguous square miles for Beaufort County, South Carolina.

The data was delivered in the South Carolina State Plane (International Feet) coordinate system, horizontal datum NAD83 (NSRS 2007), vertical datum NAVD88, Geoid 09, Feet.

Lidar ground points for each flightline generated by an automatic classification routine are used.

LiDAR sensor data were collected with the Optech ALTM3100EA LiDAR system. No imagery was requested or delivered.

Deliverables for the project included a raw (unclassified) calibrated LiDAR point cloud, survey control, and a final control report.

Overall the LiDAR data products collected by LMSI meet or exceed the requirements set out in the Statement of Work.

The quality control requirements of LMSIs quality management program were adhered to throughout the acquisition stage of this project to ensure product quality.

LIDAR acquisition began on March 6, 2013 (julian day 065) and was completed on April 20, 2013 (julian day 079). A total of 16 survey missions were flown to complete the project.

The flight plan was flown as planned with no modifications. There were no unusual occurrences during the acquisition and the sensor performed within specifications. There were 203 flight lines required to complete the project.

Project coverage was checked on site with no data gaps except for water features.

Two base stations were utilized. The base station in the north west portion of the project was named G7_203. The base station on the central portion of the project was named GG.

Thirty (30) static points were surveyed at various locations throughout the project to be utilized for quality control and adjustment of the LiDAR data. All airborne trajectories were very high quality with forward/reverse separation between 2cm-5cm.

All equipment performed within specifications with no unusual occurances or anamolies. All data was of a very high quality and the project was executed as planned.

Dewberry utilizes a variety of software suites for inventory management, classification, and data processing. All LiDAR related processes begin by importing the data into the GeoCue task management software. The swath data is tiled according to project specifications (5000 ft x 5000 ft). The tiled data is then opened in Terrascan where Dewberry uses proprietary ground classification routines to remove any non-ground points and generate an accurate ground surface. Before the actual ground routine is run points with scan angles greater than plus or minus 18 degrees are classified to class 11, withheld. Due to these higher scan angles these points have the potential to introduce issues into the ground and are therefore not used in the final ground surface. The ground routine consists of three main parameters (building size, iteration angle, and iteration distance); by adjusting these parameters and running several iterations of this routine an initial ground surface is developed. The building size parameter sets a roaming window size. Each tile is loaded with neighboring points from adjacent tiles and the routine classifies the data section by section based on this roaming window size. The second most important parameter is the maximum terrain angle, which sets the highest allowed terrain angle within the model. Once the ground routine has been completed a manual quality control routine is done using hillshades, cross-sections, and profiles within the Terrasolid software suite. After this QC step, a peer review and supervisor manual inspection is completed on a percentage of the classified tiles based on the project size and variability of the terrain. After the ground classification corrections were completed, the dataset was processed through a water classification routine that utilizes breaklines compiled by Dewberry to automatically classify hydrographic features. The water classification routine selects ground points within the breakline polygons and automatically classifies them as class 9, water. During this water classification routine, points that are within 1 foot of the hydrographic features are moved to class 10, an ignored ground due to breakline proximity.

The fully classified dataset is then processed through Dewberry's comprehensive quality control program.

The data was classified as follows:

Class 1 = Unclassified. This class includes vegetation, buildings, noise etc.

Class 2 = Ground

Class 7 = Noise

Class 8 = Model Key Points

Class 9 = Water

Class 10 = Ignored

Class 11 = Withheld Points

Class 13 = Bridges and Culverts

The LAS header information was verified to contain the following:

Class (Integer)

Adjusted GPS Time (0.000001 seconds)

Easting (0.001 ft)

Northing (0.001 ft)

Elevation (0.001 ft)

Echo Number (Integer 1 to 4)

Echo (Integer 1 to 4)

Intensity (8 bit integer)

Flight Line (Integer)

Scan Angle (Integer degree)

Dewberry used GeoCue software to develop raster stereo models from the LiDAR intensity. The raster resolution was 1 foot.

LiDAR intensity stereopairs were viewed in 3-D stereo using Socet Set for ArcGIS softcopy photogrammetric software. The breaklines are collected directly into an ArcGIS file geodatabase to ensure correct topology. The LiDARgrammetry was performed under the direct supervision of an ASPRS Certified Photogrammetrist. The breaklines were stereo-compiled in accordance with the Data Dictionary.

Single line drains, dual line drains, inland ponds and lakes, tidal waters, and edge of roads were collected according to specifications for the Beaufort County Project.

Breaklines are reviewed against LiDAR intensity imagery to verify completeness of capture. All breaklines are then compared to ESRI terrains created from ground only points prior to water classification. The horizontal placement of breaklines is compared to terrain features and the breakline elevations are compared to LiDAR elevations to ensure all breaklines match the LiDAR within acceptable tolerances. Some deviation is expected between breakline and LiDAR elevations due to monotonicity, connectivity, and flattening rules that are enforced on the breaklines. Once completeness, horizontal placement, and vertical variance is reviewed, all breaklines are reviewed for topological consistency and data integrity using a combination of ESRI Data Reviewer tools and proprietary tools. Corrections are performed within the QC workflow and re-validated.

Class 2, ground, and class 8, model key points, LiDAR points are exported from the LAS files into an Arc Geodatabase (GDB) in multipoint format. The 3D breaklines (single line drains, dual line drains, connectors, inland ponds and lakes, and tidal waters) and the project boundary are imported into the same GDB. An ESRI Terrain is generated from these inputs. The surface type of each input is as follows:

Ground Multipoint: Masspoints

Boundary: Soft Clip

Connectors: Hard Line

Single Line Drains: Hard Line

Dual Line Drains: Hard Line

Inland Lakes and Ponds: Hard Replace

Tidal Water: Hard Line

The ESRI Terrain is converted to rasters. The rasters are created to pre-defined extents so that multiple rasters are created over the project area. Creating multiple rasters rather than one large raster over a large project area makes the data more maneageable to work with. The rasters are created with 2 tiles of overlap. This allows us to ensure seamless coverage and edge-matching in the final product. These rasters were created with a 5 foot cell size using floating point output cell values and natural neighbors interpolation.

The DEMs that are created over large areas are reviewed in ArcGIS with hillshades. Hillshades allow the analyst to view the DEMs in 3D and to more efficiently locate and identify potential issues. The first review is done on the area DEMs as this increases the efficiency of any corrections that may be performed. Performing corrections on area DEMs allows the analyst to perform corrections on multiple tiles at once and helps prevent errors from occurring along individual tile seamlines. Analysts review the area DEMs for incorrect water elevations and artifacts that are introduced during the raster creation process.

The corrected and final area DEMs are clipped to not exceed maximum size criteria. DEMs are provided with a slight overlap to ensure complete coverage.

The NOAA Office for Coastal Management (OCM) received the DEM files from the South Carolina Department of Natural Resources (SC DNR). The data were in SC State Plane (NAD83 2007) with horizontal units in international feet and NAVD88 (Geoid 09) elevations in U.S. Survey feet. The bare earth hydro-flattened raster files were at a 5 ft grid spacing.

OCM performed the following processing on the data for Digital Coast storage and provisioning purposes:

1. The DEMs were exported from proprietary ESRI File Geodatabase to 32-bit floating point GeoTIFF format using ArcGIS

2. Global Mapper was then used to create tiles from the single, county-wide DEMs

3. Gdal_translate was used to assign the correct EPSG codes to each tiled file

4. The raster files were copied to database and https for Digital Coast storage and provisioning purposes