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

IGIC - Indiana GIS LiDAR Applications

for Surveyors

3. Accuracy and Limitations of using LiDAR, DEM and Derivative Products

Robert N. Wilkinson, IDNR (GIS Bob)


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.


for Surveyors


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

http://www.fgdc.gov/standards/projects/FGDC-standards-projects/accuracy/part3/chapter3


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.



for Surveyors

3.C How to compute the vertical accuracy of your AOI and Derivative Data

Products


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


Independent Vertical Accuracy Testing

Haw Creek 2010 Data

2003 Data not used in NSSDA Test


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.


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.


Points Needed for Modeling Bridge

HEC-RAS

99 Total Points


Typical Bridge Section


Weeded Down to 3 Points

Surveyed Value Left – LiDAR Value Right


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.


Add LiDAR Value to Point File with ArcMap


Attribute Table


Check Statistics in ArcMap


NSSDA Test in Excel

NSSDA at 95% Confidence Level is RMSE times 1.96

E – D = F 2F

Square Root of MSEAverage of G


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.


• 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


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).


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.


•Questions?

Date post:	25-Feb-2016
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IGIC - Indiana GIS LiDAR Applications for Surveyors

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