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LiDAR Elevation Data: Sauk County, WI 2020

Identification Information

Citation
Title
LiDAR Elevation Data: Sauk County, WI 2020
Originator
U.S. Geological Survey
Creation Date
2020-04-16
Publication Date
2020-04-16
Edition
2020
Abstract
This data represents LiDAR elevation information for Sauk County, Wisconsin in 2020. The following derivative products are available: classified LAS, hydro breaklines, and a tiled DEM (2ft). Also included are several countywide products created by the WisconsinView Partners - the WI Department of Administration’s Geographic Information Office in collaboration with the UW-Madison Space Science and Engineering Center’s (SSEC) WisconsinView repository. Original lidar data in tiled format from federal (USGS 3DEP) and/or local county lidar projects were used to create countywide mosaics of specific datasets such as DEMS, Intensity values and DSMs in various projections and coordinate systems. [The Sauk County lidar project area covers approximately 906 square miles which includes a 100 meter buffer around the county boundary. The lidar data was acquired at a nominal point spacing (NPS) of 0.907 meters and an aggregate nominal point density (ANPD) of 2.0. Project specifications are based on Sauk County requirements and on the U.S. Geological Survey National Geospatial Program LiDAR Base Specification, Version 2.1. The data was developed based on a horizontal projection/datum of NAD83(2011) / WISCRS Sauk (ftUS) (EPSG Code: 7631), and vertical datum of NAVD88 - Geoid12B (Feet). LiDAR data was acquired using a Riegl LMS-Q1560 sensor with serial number SN1264 from April 11, 2020 to April 21, 2020 in 3 total lifts. Acquisition occurred with leaves absent from deciduous trees, when no snow was present on the ground, and with rivers at or below normal levels.]
Purpose
This data is intended for reference and mapping purposes, and may be used for basic applications such as viewing, querying, and map output production, or to provide a basemap to support graphical overlays and analysis with other spatial data. [This data, along with its derivatives, is the result of a countywide elevation mapping with cooperative partnerships from Sauk County, Wisconsin DOA, and the USGS 3DEP program. This data was produced from lidar data collected in April 2020, which was processed and delivered in 2021.]
Supplemental Information
Data is available for download from: https://bin.ssec.wisc.edu/pub/wisconsinview/lidar/Sauk_2020_3DEP_Delivery/ Detailed, original metadata accompanying this LiDAR data is available inside the ‘Metadata’ folder from WisconsinView. Classified LAS: Point classification using semi-automated techniques on the point cloud to assign the feature type associated with each point. Lidar points can be classified into a number of categories including bare earth or ground, top of canopy, and water. The different classes are defined using numeric integer codes in the LAS files. Hydro Breaklines: Breaklines maintain the definition of water-related features in an elevation model. They are used to capture linear discontinuities in the surface, lake shorelines, single-line drains for small rivers, and double-line drains for large rivers. [Coupled with the classified lidar point cloud this data set is the 2010 digital terrain model.] Tiled Digital Elevation Model (DEM): A Digital Elevation Model (DEM) represents the bare-Earth surface, removing all natural and built features. The data contains (possibly) hundreds of individual files available to download as small tiled geographic areas over the extent of an entire county.
Temporal Extent
Time Instant
2020-04-16T00:00:00
Bounding Box
West
-90.325859
East
-89.585622
North
43.652222
South
43.134822
ISO Topic Category
elevation
Place Keyword
Sauk County
Wisconsin
Place Keyword Thesaurus
GNS
Theme Keyword
Digital elevation models
Theme Keyword Thesaurus
LCSH
Theme Keyword
Lidar
Grids
Contours
Surface models
Terrain models
Relief models
Hydrography
Topography
Elevations
Theme Keyword Thesaurus
LCSH
Resource Constraints
Use Limitation
Although this data is being distributed by the University of Wisconsin-Madison, no warranty expressed or implied is made by the University as to the accuracy of the data and related materials. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the University in the use of this data, or related materials. [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.]
Status
completed
Maintenance and Update Frequency
unknown
Language
eng
Credit
U.S. Geological Survey
Point of Contact
Contact
U.S. Geological Survey
Point of Contact
Contact
Ayres Associates
Delivery Point
5201 E Terrace Drive, Suite 200
City
Madison
Administrative Area
WI
Postal Code
53718
Country
US
Phone
(608) 443-1200

Spatial Reference Information

Reference System Identifier
Code
7631
Code Space
EPSG
Version
9.7

Data Quality Information

Absolute External Positional Accuracy
Lineage
Process Step
Description
LiDAR processing utilizes several software packages, including GeoCue and the TerraSolid suite of processing components. The GeoCue software is a database management system for housing the LiDAR dataset (usually multiple gigabytes in size). GeoCue incorporates a thorough checklist of processing steps and quality assurance/quality control (QA/QC) procedures that assist in the LiDAR workflow. The TerraSolid software suite is used to automate the initial classification of the LiDAR point cloud based on a set of predetermined parameters. Lidar technicians refer to ground cover research (natural and cultural features) within the project area and determine algorithms most suitable for the initial automated LiDAR classification. (Some algorithms/filters recognize the ground in forests well, while others have greater capability in urban areas). During this process each point is given an initial classification (e.g., as ground, vegetation, or noise) based on the point's coordinates and the relation to its neighbors. Classifications to be assigned include all those outlined by ASPRS standards. The initial classifications produce a coarse and inexact dataset, but offer an adequate starting point for the subsequent manual classification procedure. During this step, "overlap" points are automatically classified (those originating from neighboring flightlines) using information gathered from the ABGPS and IMU data. Any duplicate points existing from adjacent flightlines are removed during this process. Hydrographic breaklines are collected using LiDARgrammetry to ensure hydroflattened water surfaces. This process involves manipulating the LiDAR data's intensity information to create a metrically sound stereo environment. From this generated "imagery", breaklines are photogrammetrically compiled. Breakline polygons are created to represent open water bodies. The LiDAR points that fall within these areas are classified as "water." All hydrographic breaklines include a 3.125 foot buffer, with the Class 2 (bare earth) points being re-classified as Class 20 (ignored ground). TerraSolid is further used for the subsequent manual classification of the LiDAR points allowing technicians to view the point cloud in a number of ways to ensure accuracy and consistency of points and uniformity of point coverage. The TIN was processed to create a GRID or digital elevation model (DEM) with 2 foot pixels.
Process Date
2020-06-22T00:00:00
Process Step
Description
The boresight for each lift was done individually as the solution may change slightly from lift to lift. The following steps describe the Raw Data Processing and Boresight process: 1) Technicians processed the raw data to LAS format flight lines using the final GPS/IMU solution. This LAS data set was used as source data for boresight. 2) Technicians first used RIEGL RiPROCESS software to calculate initial boresight adjustment angles based on sample areas selected in the lift. These areas cover calibration flight lines collected in the lift, cross tie and production flight lines. These areas are well distributed in the lift coverage and cover multiple terrain types that are necessary for boresight angle calculation. The technician then analyzed the results and made any necessary additional adjustment until it is acceptable for the selected areas. 3) Once the boresight angle calculation was completed for the selected areas, the adjusted settings were applied to all of the flight lines of the lift and checked for consistency. The technicians utilized commercial and proprietary software packages to analyze how well flight line overlaps match for the entire lift and adjusted as necessary until the results met the project specifications. 4) Once all lifts were completed with individual boresight adjustment, the technicians checked and corrected the vertical misalignment of all flight lines and also the matching between data and ground truth. The relative accuracy was less than or equal to 7 cm RMSEz within individual swaths and less than or equal to 10 cm RMSEz or within swath overlap (between adjacent swaths). 5) The technicians ran a final vertical accuracy check of the boresighted flight lines against the surveyed check points after the z correction to ensure the requirement of NVA = 19.6 cm 95% Confidence Level (Required Accuracy) was met. Point classification was performed according to USGS Lidar Base Specification 2.1, and breaklines were collected for water features. Bare earth DEMs were exported from the classified point cloud using collected breaklines for hydroflattening.
Process Date
2022-06-22T00:00:00
Process Step
Description
LiDAR processing utilizes several software packages, including GeoCue and the TerraSolid suite of processing components. The GeoCue software is a database management system for housing the LiDAR dataset (usually multiple gigabytes in size). GeoCue incorporates a thorough checklist of processing steps and quality assurance/quality control (QA/QC) procedures that assist in the LiDAR workflow. The TerraSolid software suite is used to automate the initial classification of the LiDAR point cloud based on a set of predetermined parameters. Lidar technicians refer to ground cover research (natural and cultural features) within the project area and determine algorithms most suitable for the initial automated LiDAR classification. (Some algorithms/filters recognize the ground in forests well, while others have greater capability in urban areas). During this process each point is given an initial classification (e.g., as ground, vegetation, or noise) based on the point's coordinates and the relation to its neighbors. Classifications to be assigned include all those outlined by ASPRS standards. The initial classifications produce a coarse and inexact dataset, but offer an adequate starting point for the subsequent manual classification procedure. During this step, "overlap" points are automatically classified (those originating from neighboring flightlines) using information gathered from the ABGPS and IMU data. Any duplicate points existing from adjacent flightlines are removed during this process. Hydrographic breaklines are collected using LiDARgrammetry to ensure hydroflattened water surfaces. This process involves manipulating the LiDAR data's intensity information to create a metrically sound stereo environment. From this generated "imagery", breaklines are photogrammetrically compiled. Breakline polygons are created to represent open water bodies. The LiDAR points that fall within these areas are classified as "water." Hydro-flattened breaklines were compiled for ponded water that is 2 acres or greater, permanent islands 1 acre or larger, and double lined streams with a minimum width of 20 feet. Streams break at road crossings (culvert locations). The road fills are not be removed from the DEM. Streams are not broken at bridges. When the identification of a feature as a bridge or culvert cannot be made reliably, the feature will be regarded as a culvert. Breaklines representing streams and rivers shall be smooth, continuous, and monotonic, and represent the water surface without any stair steps except for dams and rapids. All hydrographic breaklines include a 3.125 foot buffer, with the Class 2 (bare earth) points being re-classified as Class 20 (ignored ground). TerraSolid is further used for the subsequent manual classification of the LiDAR points allowing technicians to view the point cloud in a number of ways to ensure accuracy and consistency of points and uniformity of point coverage.
Process Date
2022-06-22T00:00:00

Distribution Information

Format Name
LAS, GeoTIFF, SHP
Format Version
10.5
Distributor
University of Wisconsin-Madison
Online Access
https://bin.ssec.wisc.edu/pub/wisconsinview/lidar/Sauk_2020_3DEP_Delivery/
Protocol
WWW:DOWNLOAD-1.0-http--download
Name
WisconsinView.org
Function
download

Spatial Representation Information

Vector
Topology Level
geometryOnly
Vector Object Type
surface
Vector Object Count

Metadata Reference Information

Hierarchy Level
dataset
Metadata File Identifier
89B9A9A2-CEEB-461B-AC33-55D2837C1EB2
Metadata Point of Contact
Name
Arthur H. Robinson Map Library
Position Name
Metadata Technician
Delivery Point
550 N. Park Street
City
Madison
Administrative Area
WI
Postal Code
53706
Country
US
Email
askmap@library.wisc.edu
Phone
(608) 262-1471
Metadata Date Stamp
2022-10-07
Metadata Standard Name
ISO 19139 Geographic Information - Metadata - Implementation Specification
Metadata Standard Version
2007
Character Set
utf8
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