To acquire detailed surface elevation data for use in conservation planning, design, research, floodplain mapping, dam safety assessments and elevation modeling, etc. Classified LAS files are used to show the manually reviewed bare earth surface. This allows the user to create Intensity Images, Breaklines and Raster DEM. The purpose of these lidar data was to produce high accuracy 3D hydro-flattened Digital Elevation Model (DEM) with a 2 foot cell size. These raw lidar point cloud data were used to create classified lidar LAS files, intensity images, 3D breaklines, contours, hydro-flattened DEMs as necessary.
Product: These are Contours data for CT Statewide GIS Services as part of the required deliverables for the CT Statewide GIS Services project. 1 foot contours were produced from the hydro-flattened bare earth DEM.
Geographic Extent: CT Statewide covering approximately 5,241 square miles. Dataset Description: CT Statewide GIS Services Lidar project called for the Planning, Acquisition, processing and derivative products of lidar data to be collected at a nominal pulse spacing (NPS) of 0.35 meter; coastal areas were acquired to achieve >=20 ppsm, and all other areas were acquired to achieve >=14 ppsm. Project specifications are based on the U.S. Geological Survey National Geospatial Program Base Lidar Specification, Version 2024 rev. A. The data was developed based on a horizontal datum/projection of NAD83 (2011), State Plane Connecticut, U.S. Survey Feet and vertical datum of NAVD88 (GEOID18), U.S. Survey Feet. Lidar data was delivered as processed Classified LAS 1.4 files, formatted to 23,381 individual 2,500 ft x 2,500 ft tiles, as tiled Intensity Imagery, and as tiled bare earth DEMs; all tiled to the same 2,500 ft x 2,500 ft schema. Maximium Surface Height Raster and Swath Separation Image tiles 025645_se, 080655_ne, 085655_ne, 085655_nw, 090655_nw, 110660_se, and 135665_se do not exist in the deliverables due to all of the points in the cooresponding LAS tiles being flagged as withheld. LAS file 110660_se is all water and contains no lidar returns, this file does not exist in the deliverables.
Ground Conditions: Lidar was collected in Spring 2023, while no snow was on the ground and rivers were at or below normal levels. In order to post process the lidar data to meet task order specifications and meet ASPRS vertical accuracy guidelines, Dewberry established a total of 38 ground control points that were used to calibrate the lidar to known ground locations established throughout the CT Statewide GIS Services project area. An additional 247 independent accuracy checkpoints, 145 in Bare Earth and Urban landcovers (145 NVA points), 102 in Tall Grass and Brushland/Low Trees categories (102 VVA points), were used to assess the vertical accuracy of the data. These checkpoints were not used to calibrate or post process the data.There are no credits for this item.
None. However, users should be aware that temporal changes may have occurred since this dataset was collected and that some parts of these data may no longer represent actual surface conditions. Users should not use these data for critical applications without a full awareness of its limitations. Acknowledgement of the U.S. Geological Survey would be appreciated for products derived from these data.
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Contour File Type = GDB
Contour Elevation Units = Meters
Contour Spacing: 1 foot
ground condition
None. However, users should be aware that temporal changes may have occurred since this dataset was collected and that some parts of these data may no longer represent actual surface conditions. Users should not use these data for critical applications without a full awareness of its limitations. Acknowledgement of the U.S. Geological Survey would be appreciated for products derived from these data.
No restrictions apply to these data.
Data covers the entire area specified for this project.
A visual qualitative assessment was performed to ensure data completeness and correct topological behavior. No void or missing data.
This data set was produced to meet ASPRS Positional Accuracy Standard for Digital Geospatial Data (2014) for a 10-cm RMSEz Vertical Accuracy Class.
1 foot contours were generated for each production block from the final bare earth DEMs using ArcGIS software. Contours are labeled as intermediate or index with index contours set to every 10th interval. Using ArcGIS software, the contours are validated for correct topology, including must not intersect, must not self intersect, and must not have dangles. Contours are then manually reviewed with the 3D breaklines to ensure complete coverage, correct coding, data integrity and that contours behave correctly around water bodies, water crossings, and elevated features such as overpasses. The contours are then clipped to individual tiles as creating one dataset for the entire project renders the feature class un-usable. Enclosed contours completely within building footprints were removed from the final contour dataset.
Last metadata review date: 2024-06-25
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