1. Slope Shading Techniques for LiDAR Visualization Thomas J. Pingel Department of Geography Northern Illinois University October 27-29 Illinois GIS Association 2014 Conference Lisle, IL 1

2. How can we, in an automatable way, produce visualizations and images that assist in the interpretation, analysis, and understanding of local events? 2

3. LiDAR can be used to map the local environment relatively inexpensively, and at very high resolution. 3 A Velodyne scanner mounted on a octocopter.

4. The data need a great deal of processing to be of much use. 4

5. 5 This is a LiDAR-derived Digital Surface Model (DSM) of UC Santa Barbara, represented in shaded relief.

6. Hillshaded images were developed to realistically portray the natural environment at relatively small map scales. 6 Thelin and Pike’s (1991) shaded relief map of the United States.

7. More realistic images, like hillshades, do not always perform better than prepared cartographic products. 7 They also do not translate to urban areas very well, where relief is typically low, and aspect is highly regular.

8. Kennelly and Stewart (2006) offer some methods that bring out immense detail in a DSM-derived LiDAR visualization. 8

9. 9 But we know that realism is not always best for visualizations. We also need a straightforward way for GIS users to create visualizations with this data that are useful for a variety of purposes, not just more aesthetically pleasing.

10. 10 Here, again, was the hillshaded visualization of the DSM.

11. 11 This is a PSSM of the same data.

12. PSSMs are based on the idea of “cognitive slope.” People exaggerate the vertical component of slope by a factor of 2.3x. 12 (Pingel 2010, following Proffitt et al. 1995)

13. 13

14. Perceptually Shaded Slope Maps (PSSMs) Slope is exaggerated, then mapped to graytone Resulting appearance looks hand-drawn, which speaks to its efficacy as a visualization No spatial displacement errors common with orthophotos Offers a higher contrast image than hillshade, with better affordance for color overlay Most appropriate for mixed / urban environments How do we assess performance? – Response time and accuracy in representative map use tasks. 14

15. Cartographica (in press) 5 visualizations – hillshade, vertically exaggerated hillshade, hypsometric tint, orthophoto, and PSSM 3 map tasks – Profile estimation task to test communication of relief (or intelligibility of the image) – Two map rotation tasks to test saliency 68 participants – Extra credit in introductory geography classes 15

16. Profile Estimation 16

17. Mental Rotation 17

18. 18 Profile Estimation Results

19. Controlling Variability 106 participants More direct comparisons between PSSM and hillshade Related tasks 19

20. Profile Estimation 20 Both accuracy rates and response time paired t-tests t(105) > 2.94, p 0.57

21. Map Rotation 21 Accuracy rates paired t-test t(105) > 3.05, p = 0.003, Cohen’s d = 0.59

22. Last year, we successfully used PSSMs in combination with our LiDAR filter SMRF to visually explore the forest floor of the ancient Maya site, El Pilar. 22

23. Last year, we successfully used PSSMs in combination with our LiDAR filter SMRF to visually explore the forest floor of the ancient Maya site, El Pilar. 23

24. Conclusions The PSSM is empirically effective for visualization of LiDAR-derived DSMs Automatically generated – Used in support of disaster relief and incident response Easy to produce in any GIS software – Python-based plug-in modules to come 24

25. Future Work Data was also collected to analyze: – Sex – Previous geography experience – Ability on related tasks Eye tracking studies to determine how visualizations are used Test potential for overlay support New LiDAR unit to generate higher resolution images – Mixed indoor and outdoor environments 25

26. Acknowledgments Illinois Geographical Society Research Grant Ben Maloney, Graduate Research Assistant Stacy Terlep, Undergraduate Research Assistant 26