1. LIDAR and TDS in GIS
A Comparison of Channel Geometry Profiles Created from Remotely Sensed and On-the-Ground Survey Data
(or..how a programmer in China made life easy) By
Jason S. Alexander
Department of Aquatic, Watershed and Earth Resources
Utah State University ?

2. Quick Map Purpose of research and analysis
Data origins / advantages and disadvantages
Methods of analysis
Results
Conclusions and Improvements

3. Location of Research
Lodore Canyon, CO

4. Basic Purpose of Research
Determine the effects of Flaming Gorge Dam and invasive riparian vegetation on channel planform

5. Basic Purpose of this Analysis
Compare total station (TDS) survey data with remotely sensed (LIDAR) data
Assuming TDS is the control we want to know the relative reliability of LIDAR for analysis of channel planform changes.

6. Data Origins - TDS
Laser total station survey data of established permanent cross sections in experimental reaches of Lodore Canyon (May 2005)

7. Data Origins - TDS
Precision of <2 cm within local grids (no real-world coordinates…yet)

8. Advantages - TDS Extreme accuracy and precision Low cost
Can be coupled with sonar data
Integrated research
Allows for graduate students to leave their desk for extended periods

9. Disadvantages - TDS Generally in 2D (repeated profiles)
Cumbersome and time consuming for 3D topography
Requires large crews for efficiency
Not in real world coordinates
Risky (data and health)

10. Data Origins - LIDAR
LIght Detection And Ranging (LIDAR) performed in experimental reaches of Lodore Canyon, April 2005

11. Data Origins - LIDAR
Accuracy of ~15cm vertical and 1m horizontal

12. Advantages - LIDAR
Data saturation (millions of points with 15cm vertical accuracy over large area)
Can be coupled with high-resolution aerial photography
Large scale volumetric analysis
Minimal logistics, just money

13. Disadvantages - LIDAR Expensive (especially for repeats)
15 cm vertical accuracy means significant error in volumetric analysis and water surface elevation
No sub-aqueous data
Graduate students stay at their desk

14. Methods
Translate and rotate local grids into real-world coordinates

15. Methods
Translate and rotate local grids into real-world coordinates

16. Methods
Create TIN from LIDAR survey points

17. Methods
Create TIN from LIDAR survey points

18. Methods
Cut profiles and export coordinates…easy?…NO!

19. Methods
3D Analyst does not (with standard tools) export XYZ coordinates from profiles!

20. Methods
A search of the ESRI support center finds this is a common problem!

21. Methods
Then came Min-Lang Huang! Author of the EZ Profiler….

22. Methods
EZ Profiler V8.3 is an independent extension (does not need 3D analyst)!

23. Methods
Profiles can be sampled at equal intervals or with set number of points

24. EZ Profiler Cross Section Point Shapefile
Methods
Shapefiles are created for each profile
EZ Profiler Cross Section Point Shapefile

25. Methods
Attributes include Northing, Easting, Elevation, and Distance

26. Attribute table “export to Excel” button
Methods
Attribute tables can be easily exported to Excel!
Attribute table “export to Excel” button

27. Methods
Then compared to TDS survey data!

28. Results
General profile shapes are comparable, but…..

29. Results
No specific patterns were found in the behavior of LIDAR vs. TDS

30. Results
“Eyeballing” profiles works out, but what about the accuracy?

31. Results
Spot checks reveal significant differences in elevations

32. Results
Profile width also exhibits large variance

33. Results
Water surface elevation data from LIDAR is not reliable

34. Improvements
Use differential GPS to aquire real-world coordinates for local grids
Ground surface at each LIDAR ground target
EZ Profiler + “Snapping”

35. Conclusions
TINs created from LIDAR provide equivalent or superior profile shapes
Evaluation of accuracy is difficult (if not impossible) without improvements
LIDAR data are unreliable for water surface elevation

36. Refs / Acknowledgments
Min-Lang Huang : author of EZ Profiler software !
Dr. Tarboton for assistance with TIN creation

37. Questions or Comments?