Contour Lines (2007) derived from LiDAR terrain model

Horizontal accuracy is +/- 3.8-foot at the 95% confidence level using RMSE(r) x 1.7308  as defined by the FGDC Geospatial Positional Accuracy Standards, Part 3: NSSDA.

0.3-feet RMSE for unobscured ground points. 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 and filtered LiDAR data points. Filtered LiDAR data has had vegetation and cultural features removed and by analysis represents bare earth elevations.  The RMSE figure was used to compute the vertical National Standard for Spatial Data Accuracy (NSSDA).

The LiDAR Project Survey was acquired for the Florida Division of Emergency Management and processed by Woolpert Inc. To collect the breaklines, the LiDAR data was used as the main source data set in addition to orthophotography. Orthophoto imagery for the area within Lee County was from new imagery collected and developed by the Woolpert Team. All imagery for Lee County is dated 2007 with a 0.5-foot pixel resolution. Orthophoto imagery for the areas within Charlotte County was provided by FDEM, and was provided at 1.0-foot pixel resolution and dated 2006.

The Airborne Global Positioning System (ABGPS), inertial measurement unit (IMU), and raw scans are collected during the LiDAR aerial survey. The ABGPS monitors the xyz position of the sensor and the IMU monitors the orientation. During the aerial survey laser pulses reflected from features on the ground surface are detected by the receiver optics and collected by the data logger. GPS locations are based on data collected by receivers on the aircraft and base stations on the ground. The ground base stations are placed no more than 20 mile radius from the flight survey area.

The ABGPS, IMU, and raw scans are integrated using proprietary software developed by the Leica Geosystems and delivered with the Leica ALS50 System. The resultant file is in a LAS binary 1.1 file format. The LAS file format can be easily transferred from one file format to another.  It is a binary file format that maintains information specific to the LiDAR data (return#, intensity value, xyz, etc.). The resultant points are produced in the Florida State Plane West Zone coordinate system, with units in feet and referenced to the NAD83/90 HARN horizontal datum and NAVD88 vertical datum.

The unedited data are classified to facilitate the application of the appropriate feature extraction filters. Interactive editing methods are applied to those areas where it is inappropriate or impossible to use the feature extraction filters, based upon the design criteria and/or limitations of the relevant filters. These same feature extraction filters are used to produce elevation height surfaces. Point classification: Class1 = Unclassified, Class2 = Ground, Class7 = Noise, Class9 = Water, Class12 = Overlap

Filtered LiDAR and vector data are subjected to rigorous QA/QC procedures designed by Woolpert. Stereo imagery was created from the LiDAR surface and orthophoto imagery using GeoCue software. From these stereo images, or LiDARgrammetry, breakline features were collected along linear topographic features as required. Breakline elevations were linearly ramped between identified critical elevation points. 

The contours are generated from LiDAR data and breaklines using a contour generation function in TerraScan. The LiDAR data is gridded to a 30' grid and incorporated with the 3d breaklines. A process is run to remove the gridded point from within 15' of the breaklines and TerraScan automatically generates the contours using specific input criteria to include contour interval, line type, smoothness and minimum size.

Dataset copied.