igic - indiana gis lidar applications for surveyors
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IGIC - Indiana GIS LiDAR Applications for Surveyors. 3. Accuracy and Limitations of using LiDAR, DEM and Derivative Products Robert N. Wilkinson, IDNR (GIS Bob). IGIC - Indiana GIS LiDAR Applications for Surveyors. Accuracy and Limitations of using LiDAR, DEM and Derivative Products - PowerPoint PPT PresentationTRANSCRIPT
Coordination of Indiana GIS through dissemination of data and data products, education and outreach, adoption of standards, and building partnerships
IGIC - Indiana GIS LiDAR Applications
for Surveyors
3. Accuracy and Limitations of using LiDAR, DEM and Derivative Products
Robert N. Wilkinson, IDNR (GIS Bob)
Coordination of Indiana GIS through dissemination of data and data products, education and outreach, adoption of standards, and building partnerships
Accuracy and Limitations of using LiDAR, DEM and Derivative Products
FGDC Metadata [and Published Accuracy]for Indiana’s LiDAR & DEM data products
IN_2011_Statewide_East_LAS.txtIN_2011_Statewide_West_LAS.txt
IN_2011_Statewide_East_IMG_DEM.txtIN_2011_Statewide_West_IMG_DEM.txt
IN_2011_Statewide_East_Breakline.txtIN_2011_Statewide_West_Breakline.txt
Published Accuracy: The LiDAR data vertical accuracy RMSE is Block 1 - 5.699 cm (0.187 ft), Block 2 - 7.345 cm (0.241 ft) and Block 3 - 6.553 cm (0.215 ft). The data collected under this Task Order meets the National Standard for Spatial Database Accuracy (NSSDA) accuracy standards.
IGIC - Indiana GIS LiDAR Applications
for Surveyors
Coordination of Indiana GIS through dissemination of data and data products, education and outreach, adoption of standards, and building partnerships
NSSDA Accuracy Testing
http://www.fgdc.gov/standards/projects/FGDC-standards-projects/accuracy/part3/chapter3
View Here
National Standard for Spatial Data Accuracy
Issued by FGDC in 1998
Coordination of Indiana GIS through dissemination of data and data products, education and outreach, adoption of standards, and building partnerships
NSSDA
• Objective
The National Standard for Spatial Data Accuracy (NSSDA) implements a statistical and testing methodology for estimating the positional accuracy of points on maps and in digital geospatial data, with respect to georeferenced ground positions of higher accuracy.
Coordination of Indiana GIS through dissemination of data and data products, education and outreach, adoption of standards, and building partnerships
IGIC - Indiana GIS LiDAR Applications
for Surveyors
3.C How to compute the vertical accuracy of your AOI and Derivative Data
Products
Coordination of Indiana GIS through dissemination of data and data products, education and outreach, adoption of standards, and building partnerships
Independent Vertical Accuracy Testing
(Using Existing DNR Survey Data)
IDNR Projects from 2007 – 2010
Mostly from Work Done for FEMA MapMod Projects
In Various Locations Around the State
In One Location, More or Less in a County
Coordination of Indiana GIS through dissemination of data and data products, education and outreach, adoption of standards, and building partnerships
Independent Vertical Accuracy Testing
Haw Creek 2010 Data
2003 Data not used in NSSDA Test
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Haw Creek 2010 Data
Project from 2010May have been some changes between survey and LiDAR -Road resurfaced, erosion, Cut/fill areas
3422 Total PointsToo many points. NSSDA only requires 20
Some points on guardrails, bridge low structure etc. not suitable for checking LiDAR data.
Coordination of Indiana GIS through dissemination of data and data products, education and outreach, adoption of standards, and building partnerships
Testing Methodology• Data Producer will determine Geographic
extent of testing area.• 20 points required for area. • Point placement
Better to spread through entire area Evenly dispersed in four quadrants 10% across entire length of box
• Concentration can be heavier in specific areas
• User can concentrate more points in specified area when warranted by job requirements.
Coordination of Indiana GIS through dissemination of data and data products, education and outreach, adoption of standards, and building partnerships
Points Needed for Modeling Bridge
HEC-RAS
99 Total Points
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Typical Bridge Section
Coordination of Indiana GIS through dissemination of data and data products, education and outreach, adoption of standards, and building partnerships
Weeded Down to 3 Points
Surveyed Value Left – LiDAR Value Right
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Results of Weeding Down Points
• 3428 Points were Weeded down to about 210 Points.
• Several more points weeded by looking at their attributes to confirm that they were not ground points. 203 Points Remain.
Coordination of Indiana GIS through dissemination of data and data products, education and outreach, adoption of standards, and building partnerships
Add LiDAR Value to Point File with ArcMap
Coordination of Indiana GIS through dissemination of data and data products, education and outreach, adoption of standards, and building partnerships
Attribute Table
Coordination of Indiana GIS through dissemination of data and data products, education and outreach, adoption of standards, and building partnerships
Check Statistics in ArcMap
Coordination of Indiana GIS through dissemination of data and data products, education and outreach, adoption of standards, and building partnerships
NSSDA Test in Excel
NSSDA at 95% Confidence Level is RMSE times 1.96
E – D = F 2F
Square Root of MSEAverage of G
Coordination of Indiana GIS through dissemination of data and data products, education and outreach, adoption of standards, and building partnerships
NSSDA Test Results
• Bartholomew – 0.58 ft. • Brown – 0.67 ft. • Boone – 0.32 ft. • Cass – 0.47 ft. • Clinton – 0.33 ft. • Elkhart – 0.81 ft.• Howard – 0.30 ft.• Johnson – 0.47 ft.• Monroe – 0.72 ft.• Morgan – 0.23 ft.
Coordination of Indiana GIS through dissemination of data and data products, education and outreach, adoption of standards, and building partnerships
• IGIC would like to create a tracking system for public use that visually shows where LiDAR data has been checked against survey data.
• Using qualified survey data, either previously collected or specifically collected for running elevation checks: Be willing to run checks through the process Be able to describe the reasoning behind how
the process was done with used points. Be willing to share data sheets and description
of area checked to IGIC (free of charge).
Index for Accuracy Reporting
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Accuracy Reporting
• Will be included in index Metadata – Index will be shapefile designed to visually
depict area checked. Shapefile attributed with pertinent data
Vertical datum Date of check Check performed by
• Example in metadata - 0.58 ft. at a 95% confidence level, derived
according to NSSDA, i.e., based on RMSE of 0.30 ft. in the open terrain land cover category (Note USGS V1.2 Specification).
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Hydro Flattening.
• HYDRO FLATTENING:• Potential loss of some data.
Only the DEM’s derived from the LAS files.
• Breaklines digitized from the LAS files. Point clouds are not as sharp as the orthophotos.
• A little bit of land may accidently get flattened while a little bit of water may not.
• Should now be just ± 10 feet.
Coordination of Indiana GIS through dissemination of data and data products, education and outreach, adoption of standards, and building partnerships
•Questions?