LiDAR Elevation, Blue Earth County, Minnesota, 2005

This page last updated: 09/14/2012
Metadata created using Minnesota Geographic Metadata Guidelines


Go to Section:
1. Overview
2. Data Quality
3. Data Organization
4. Coordinate System
5. Attributes
6. Distribution - Get Data
7. Metadata Reference

Section 1 Overview
Originator Optimal Geomatics, Inc.
Title LiDAR Elevation, Blue Earth County, Minnesota, 2005
Abstract The original data was classified bare-earth LiDAR DEM and photogrammetrically derived breaklines generated from LiDAR Intensity stereo-pairs in ESRI ASCII 3D Generate format and Microstation SE .dgn format for Blue Earth County, Minnesota. The data was further processed by the Minnesota Department of Natural Resources to create and distribute feature classes in this geodatabase version.

The LiDAR data for Blue Earth County was collected under contract by the county. Thus, the data format is not entirely consistent with some of the other LiDAR data available in Minnesota. Specifically, the Blue Earth county collect only required classification of Bare Earth in the LiDAR LAS files, so there is no information on buildings, vegetation, or model key points.

Breaklines captured as part of this effort are also a bit different since they are 3D Polyline features rather than 3D Polygon features. They also include road centerlines, stream courses and other features that are not part of the Statewide collect specifications.

Note: This metadata record was created at the Minnesota Geospatial Information Office using information supplied by Optimal Geomatics, Inc., Blue Earth County, and the Minneosta Department of Natural Resources.
Purpose The purpose of the bare-earth LiDAR point and breakline data is to provide a surface model capable of supporting the generation of 2-foot contours.
Time Period of Content Date 2005
Currentness Reference April 13-14 and 23-24, 2005
Progress Complete
Maintenance and Update Frequency Unknown
Spatial Extent of Data Blue Earth County, Minnesota
Bounding Coordinates -94.379
-93.768
44.270
43.842
Place Keywords Blue Earth County, Minnesota
Theme Keywords elevation, LiDAR, DEM, digital elevation model, contour, topographic, topo, DTM, LAS, breakline
Theme Keyword Thesaurus ISO 19115
Access Constraints None
Use Constraints See Disclaimer field for complete use conditions.
Contact Person Information Charles Berg, IT Director
Blue Earth County, Minnesota
410 S. 5th Street, #075, PO Box 8608
Mankato, MN  56002-8608
Phone: 507-389-8204
Fax: 507-389-8355
Email:
Browse Graphic None available
Associated Data Sets For more information about elevation data for Minnesota, see: www.mngeo.state.mn.us/chouse/elevation/index.html

Section 2 Data Quality
Attribute Accuracy LiDAR DEMs have a maximum RMSE of 15 centimeters, which is roughly equivalent to 1-foot accuracy. Field verification of the vertical accuracy of the LiDAR DEM was conducted to ensure that the 15-centimeter RMSE requirement was satisfied for all major vegetation categories that were predominate within the project area.

The RMSE calculated from a sample of test points is not the RMSE of the DEM. The calculated value may be higher or it may be lower than that of the DEM. Confidence in the calculated value increases with the number of test points. If the errors (lack of accuracy) associated with the DEM are normally distributed and unbiased, the confidence in the calculated RMSE can be determined as a function of sample size. Similarly, the sample RMSE necessary to obtain 95-percent confidence that the DEM RMSE is less than 15 centimeters can also be determined as a function of sample size. Optimal Geomatics collected test points using RTK (Real-Time Kinematic) GPS techniques. Nine hundred and twenty points were collected in total over various terrain classes. All RMSE calculations were performed on the bare-earth, orthometric surface.
Logical Consistency LiDAR was classified and stereo-pairs were generated from LiDAR intensity data to enhance the surface with breaklines in order to produce a DTM surface which will support the generation of 2-foot contours.
Completeness The surface coverage fulfills Blue Earth County's boundary limits as requested.
Horizontal Positional Accuracy No specific testing was done to determine horizontal accuracy of the DTM. Test results for vertical accuracy tend to show that the 0.92 meter (3.01 U.S. survey feet) RMSE horizontal accuracy tolerance determined by system studies and other methods was met or exceeded.

Expected horizontal accuracy of elevation products as determined from system studies
and other methods is 1/2000th of the flight height, which in the instance of this particular
project was 1836 meters (6023.6 U.S. survey feet) AGL (above ground level), giving a horizontal tolerance of less than 0.92 meters (3.01 U.S. survey feet).
Vertical Positional Accuracy RMSE: 0.37 feet (0.11 meters) / NSSDA: 0.72 feet (0.22 meters). Meets or exceeds ASPRS Class 1 accuracy standards for the development of 2.0-foot contours.

Tested 0.37 feet (0.11 meters) limiting RMSEz fundamental vertical accuracy. These results reported in NSSDA terms are 0.72 feet (0.22 meters) fundamental vertical accuracy at 95 percent confidence level in open terrain using RMSE(z) x 1.9600. ASPRS Class 1 standards require a limiting RMSEz of 1/3 of the contour interval for well defined points (0.67 feet).
Lineage Optimal Geographics Processing Steps:

The LiDAR data was imported into a project using TerraScan (Terrasolid, Ltd.) and the project management tool Geocue (NIIRS10). By creating a project, the various flightlines are combined while breaking the dataset as a whole into manageable pieces. This process also converted the dataset from geographic coordinates to the Blue Earth County Coordinate System (NAD83), US Survey Feet, NAVD88, US Survey Feet. The ellipsoidal height values were converted to NAVD88 orthometric values using the Geoid03 model provided by NGS. The lines were then checked against adjacent lines. The data was also checked against the validation points across the project area. The results of these checks showed the DEM fitting the validation points well. See LiDAR DEM Quality Control Report for results. The data from each line was then combined and classification routines were run to determine the initial surface model. This initial surface model was then reduced and breaklines were collected using Optimal's proprietary methods to create the final bare-earth dataset. A Triangulated Irregular Network (TIN) was produced and 2-foot contours were subsequently generated from the TIN to validate the LiDAR classification. Final data was exported to ASCII ESRI 3D Generate files and Microstation SE dgn files.

Derived Products:
The breakline and point feature class data were projected from Blue Earth county coordinates to UTM coordinates and the vertical units were converted from feet to meters. These feature classes were then combined with a boundary feature class into a ESRI Terrain data structure.

The one-meter DEM in the file geodatabase elevation_data.gdb was created from the aforementioned Terrain data using standard ArcMAP tools. This one-meter raster was then reduced to 3 meters using the Aggregate function of ArcMAP. A cell factor of three and a MEAN aggregate option were used.

Minnesota Department of Natural Resources Processing Steps:

1) Generate files were converted to Feature classes in ArcMap
2) Feature classes were projected from County Coordinates to UTM Zone 15, NAD83
3) Z values were scaled from feet to meters and merged into a single feature class
4) Breakline features were merged together into a single feature class
5) Breakline features were projected from County Coordinates to UTM Zone 15, NAD83
6) Breakline Z Values were scaled from feet to meters
7) Bare Earth Point feature class and breaklines were used to create a Terrain data type
8) 1-meter DEM was derived from Terrain using nearest neighbors interpolation option (DEM01)
9) Hillshade was derived from 1-meter DEM (DEM01HS)
10) 3-meter DEM was derived from Terrain using nearest neighbors interpolation option (DEM03)
11) Hillshade was derived from 3-meter DEM (DEM03HS)
12) Aspect was derived from 3-meter DEM (DEM03ASPECT)
13) Slope in degrees was derived from 3-meter DEM (DEM03SLOPE_DEGREES)
14) Slope in percent was derived from 3-meter DEM (DEM03SLOPE_PERCENT)
15) DEM03 was smoothed using a 3x3 mean smoothing filter
16) 2-foot contours were created from the smoothed 3-meter DEM

All DEMS are hydro flattened and enforced using the breakline features

All processing was done using ArcGIS V10 and LP360 Extensions.

Section 3 Spatial Data Organization (not used in this metadata)

Section 4 Coordinate System
Horizontal Coordinate Scheme Universal Transverse Mercator
UTM Zone Number 15
Horizontal Datum NAD83
Horizontal Units meters

Section 5 Attributes
Overview
Detailed Citation
Table Detail:

Section 6 Distribution
Publisher Blue Earth County, Minnesota
Publication Date 2005
Contact Person Information Nancy Rader, GIS Data Coordinator
Minnesota Geospatial Information Office
658 Cedar Street
St. Paul, MN  55155
Phone: 651-201-2489
Email: clearing.house@state.mn.us
Distributor's Data Set Identifier Downloadable Data
Distribution Liability The DTM data represents the results of data collection/processing for Blue Earth County, Minnesota and indicates the general conditions existing at the time of flight. As such, it is only valid for its intended use, content, time and accuracy specifications. The user is responsible for the results of any application of the data other than for its intended purpose.

MnGeo's data disclaimer is online: www.mngeo.state.mn.us/chouse/disclaimer.html.
Ordering Instructions The LiDAR data provided by DNR may be downloaded from an FTP site maintained by MnGeo by clicking on the link below (recommended) or from DNR's FTP site which is not as fast. DNR provides the data as well as numerous help files on the site to assist with understanding LiDAR data and using it with GIS software.

For more help with Minnesota's LiDAR data, including a link to DNR's FTP site, see www.mngeo.state.mn.us/chouse/elevation/lidar.html
Online Linkage I AGREE to the notice in "Distribution Liability" above. Clicking to agree will either begin the download process or link to download information. See "Ordering Instructions" above for details.

Section 7 Metadata Reference
Metadata Date 09/14/2012
Contact Person Information Nancy Rader, GIS Data Coordinator
Minnesota Geospatial Information Office
658 Cedar Street
St. Paul, MN  55155
Phone: 651-201-2489
Email: clearing.house@state.mn.us
Metadata Standard Name Minnesota Geographic Metadata Guidelines
Metadata Standard Version 1.2
Metadata Standard Online Linkage http://www.mngeo.state.mn.us/committee/standards/mgmg/metadata.htm


This page last updated: 09/14/2012
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