The document discusses methods for visualizing the displacement of marine sand dunes over time using GPU techniques. It describes using locally refined B-splines to generate continuous surface representations from multi-temporal bathymetric surveys. Displacement fields can then be analyzed and visualized using glyphs rendered directly on the GPU. This allows interactive exploration and inspection of the B-spline approximations and displacement results.

1. VISUALIZATION OF MARINE SAND
DUNE DISPLACEMENTS UTILIZING
MODERN GPU TECHNIQUES
Thomas Gierlingera,b, Andre R. Brodtkorbc, Andre
Stumpfd,e, Marcel Weilera,b, Frank Michela,b
a) Fraunhofer IGD, Darmstadt, Germany
b) TU Darmstadt, Darmstadt, Germany
c) SINTEF ICT, Oslo, Norway
d) LDO, University of Western Brittany, Brest, France
e) IPGS, University of Strasbourg, Strasbourg, France

2. IQMULUS – BIG GEO DATA
• 4 year EU FP7 Research
Project (8.1 Mio EUR)
• A High-volume Fusion and
Analysis Platform for
Geospatial Point Clouds,
Coverages and Volumetric
Data Sets
• IQmulus will leverage the
information hidden in large
heterogeneous geospatial
data sets and make them a
practical choice to support
reliable decision making
• www.iqmulus.eu
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3. SAND DUNE DISPLACEMENTS
Motivation
Detection of sand dune displacements by comparing bathymetric
survey data from different points in time.
Submarine dunes and sand banks are among the most dynamic
geomorphologic formations in coastal waters. Their movement can
have significant impacts on the benthic ecosystem, marine transport
in coastal waters, and infrastructure such as pipelines and
communication cables.
Standard for the analysis of multi-temporal MBES surveys is visual
analysis by trained experts delineating the crest line of the dunes at
several time steps
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4. SAND DUNE DISPLACEMENTS
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Illustration of a manual analysis of two bathymetric surveys (Gómez et al., 2010)

5. SAND DUNE DISPLACEMENTS
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The IQmulus Solution
Generate Locally Refined B-Splines
• Continuous Surface Representation
Trim the surface to original extent
Sample the surface at selected
resolution
• Regularly gridded DEM
Analyze using image correlation
• Displacement fields

6. SAND DUNE DISPLACEMENTS
The IQmulus Solution
Generate Locally Refined B-Splines
• Continuous Surface Representation
Trim the surface to original extent
Sample the surface at selected
resolution
• Regularly gridded DEM
Analyze using image correlation
• Displacement fields
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7. VISUALIZING LR B-SPLINES
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8. VISUALIZING LR B-SPLINES
The system approximates LR B-Splines
representing the original point cloud
Check the accuracy of the approximated LR B-
Splines
Display the LR B-Spline surface together with the
original point data
How to do this interactively?
Utilize modern GPU based methods!
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9. VISUALIZING LR B-SPLINES
But …
GPUs support only polygonal meshes
• Convert the LR spline representation to a triangulation.
Uniform sampling of the surface will often either
produce too many or too few triangles.
• Too many triangles will severely impact the interactivity
• Too few triangles will dramatically reduce the quality
Use GPU hardware tesselator
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10. VISUALIZING LR B-SPLINES
• Extract Bezier coefficients of the LR B-Spline
• Render patches of the LR B-Spline Surface
• Generate triangles depending on the current view
• E.g. Screen space size of element
• Tesselate the needed triangles on the GPU for each
rendered frame
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11. VISUALIZING LR B-SPLINES
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• Review the approximated LR B-Spline Surface
• Compare with whole input point cloud
• Compare to outliers above a certain

12. VISUALIZING LR B-SPLINES
• ddd
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13. VISUALIZING DISPLACEMENT FIELDS
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14. VISUALIZING DISPLACEMENT FIELDS
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15. VISUALIZING DISPLACEMENT FIELDS
Chosen glyph for visualizing the displacement:
Visual attributes
• Direction, Length, Color, Width
Can be mapped to different data attributes
• Displacement direction, Displacement magnitude, etc.
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16. VISUALIZING DISPLACEMENT FIELDS
How and when to visualize the glyphs?
Idea: Compute the visualization interactively on the GPU
by accessing the original data.
Data available as GeoTIFF
• Displacement X
• Displacement Y
• Uncertainty
Upload the original data to the GPU and use OpenGL
Shader to evaluate data at needed positions.
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17. VISUALIZING DISPLACEMENT FIELDS
How to generate glyph on the GPU?
Adjusting quality of Glyphs
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18. VISUALIZING DISPLACEMENT FIELDS
As the generation is done on-the-fly (quality) parameters
can be changed interactively
• By the user (number, distribution and quality)
• Depending on screen space size (quality)
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19. VISUALIZING DISPLACEMANT FIELDS
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20. VISUALIZING DISPLACEMANT FIELDS
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21. VISUALIZING DISPLACEMANT FIELDS
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22. VISUALIZING DISPLACEMANT FIELDS
• gg
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23. CONCLUSION
Two approaches for interactive visualization of geospatial
data utilizing modern GPU based methods.
Analyzing intermediate and final results of a workflow to
support the user in
• Inspecting approximation results (LR B-Splines)
• Analyzing displacement fields (GPU glyphs)
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24. THANKS
Co-Authors: Thomas Gierlinger, Andre R. Brodtkorb, Andre
Stumpf, Marcel Weiler
IQmulus project partners
You for your interest in our work!
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Research leading to the results presented here is carried out within the project IQmulus
(A High-volume Fusion and Analysis Platform for Geospatial Point Clouds, Coverages
and Volumetric Data Sets) funded from the 7th Framework Programme of the European
Commission, call identifier FP7-ICT-2011-8, under the grant agreement no. 318787,
started in November 2012.

25. WANT TO KNOW MORE?
Today
• Joint Poster Session
Tomorrow
• GeoBigData @ Geospatial Week 2015
• In this same room
• Project website: http://www.iqmulus.eu
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