2007 SWFWMD Topographic Lidar: Lake Placid (FL)

SWFWMD regularly uses digital topographic information to support regulatory, land management and acquisition, planning, engineering and habitat restoration projects. LiDAR data will support hydrologic modeling activities associated with the FederalEmergency Management Agency (FEMA), and in the creation of Digital Flood Insurance Rate Maps(DFIRM). The Light Detection and Ranging (LiDAR) LAS dataset is a survey of Lake Placid. The Lake Placid LiDAR Survey project area consists of approximately 44.8 miles. The LiDAR point cloud was flown at a density sufficient to support a maximum final post spacing of 4 feet for unobscured areas. 3001 Inc. acquired 38 flightlines on March 4, 2007. The data was divided into 5000' by 5000' cells that serve as the tiling scheme. The Lake Placid LiDAR Survey was collected under the guidance of a Professional Mapper/Surveyor.

The Lake Placid 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.

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

https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/4695/supplemental/fl2007_swfwmd_lkplacid_m4695.kmz

A report for this dataset is available at:

https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/4695/supplemental/fl2007_swfwmd_lkplacid_m4695_surveyreport.pdf

LiDAR points in LAZ format (Classes 1,2,5,9)

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Any conclusions drawn from the analysis of this information are not the responsibility of USACE, Precision Aerial Reconnaissance, 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/#/lidar/search/where:ID=4695;

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Users should be aware that temporal changes may have occurred since this data set was collected and some parts of this data may no longer represent actual surface conditions. Users should not use this data for critical applications without a full awareness of its limitations. These data depict the heights at the time of the survey and are only accurate for that time.

Stream shore lines and 3-D coordinate line strings were collected as breaklines. These breaklines were created from on-screen digitizing using orthophotography. Attributes were verified using routines that verify the vertical and horizontal positions of the breaklines.

All ground control processing and adjustment is performed using published coordinate horizontal and vertical datums (e.g. NGS CORS). For deliverables, Corpscon for Windows Version 5.11.08 (geoid 99) was used for horizontal and vertical datum conversion as well as for coordinate system conversion purposes (e.g. UTM to State Plane).; Quantitative Value: 1.0 meters, Test that produced the value: 100 cm

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: 0.0366 meters, Test that produced the value: 3.66 cm RMSEz

The LAS files were flown at a density sufficient to support a maximum final post spacing of 4 feet 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 4 feet for unobscured areas. 3001 Inc. acquired 38 flightlines on March 4, 2007. The data was divided into 5000' by 5000' cells that serve as the tiling scheme. The Lake Placid LiDAR Survey was collected under the guidance of a Professional Mapper/Surveyor.