IGIC - Indiana GIS LiDAR Applications for Surveyors

1. IGIC - Indiana GIS LiDAR Applications for Surveyors 3. Accuracy and Limitations of using LiDAR, DEM and Derivative Products Robert N. Wilkinson, IDNR (GIS Bob)

2. IGIC - Indiana GIS LiDAR Applications for Surveyors 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.txt IN_2011_Statewide_West_LAS.txt IN_2011_Statewide_East_IMG_DEM.txt IN_2011_Statewide_West_IMG_DEM.txt IN_2011_Statewide_East_Breakline.txt IN_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.

3. NSSDA Accuracy Testing National Standard for Spatial Data AccuracyIssued by FGDC in 1998 http://www.fgdc.gov/standards/projects/FGDC-standards-projects/accuracy/part3/chapter3 View Here

4. 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.

5. IGIC - Indiana GIS LiDAR Applications for Surveyors 3.C How to compute the vertical accuracy of your AOI and Derivative Data Products

6. 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

7. Independent Vertical Accuracy TestingHaw Creek 2010 Data 2003 Data not used in NSSDA Test

8. Haw Creek 2010 Data Project from 2010 May have been some changes between survey and LiDAR - Road resurfaced, erosion, Cut/fill areas 3422 Total Points Too many points. NSSDA only requires 20 Some points on guardrails, bridge low structure etc. not suitable for checking LiDAR data.

9. 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.

10. Points Needed for Modeling BridgeHEC-RAS 99 Total Points

11. Typical Bridge Section

12. Weeded Down to 3 Points Surveyed Value Left – LiDAR Value Right

13. 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.

14. Add LiDAR Value to Point File with ArcMap

15. Attribute Table

16. Check Statistics in ArcMap

17. NSSDA Test in Excel E – D = F F 2 Average of G Square Root of MSE NSSDA at 95% Confidence Level is RMSE times 1.96

18. 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.

19. Index for Accuracy Reporting • 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).

20. 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).

21. 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.

22. Questions?