3 D Information cs 5764 Information Visualization Chris

3 -D Information cs 5764: Information Visualization Chris North

Where are we? • • Multi-D 1 D 2 D 3 D Hierarchies/Trees Networks/Graphs Document collections • • Design Principles Empirical Evaluation Navigation Strategies Visual Overviews

3 -D Information Examples • • Universe, space CAD/CAM, architecture Physical objects, atomic structures, scientific data physiological, MRI

Types of 3 -D Information • Surface data • 2 D analogy: vector graphics, geometric shapes • Volume data • 2 D analogy: raster graphics, bitmaps, images

Surface Data • Vector/Polygonal surface data • Polygons approximate surfaces of 3 D objects • Paint textures on surfaces • Examples: • Quake •

VRML • Protein example • http: //www. rcsb. org/pdb/cgi/explore. cgi? job=graphics&pdb. Id=4 TNA&page=&pid=16250983503380

Navigation y • Move camera (POV) • Move objects • 6 degrees of freedom (DOF): • 3 translation • 3 rotation x z y • Zoom = translate forward? x z

Zoom vs. Translation zoom translate

Graphics • Projection • Z-buffer • Shading, texture mapping, … • Ray Tracing • Shoot rays from camera into scene • Reflection, …

Challenges • Navigation • DOF • Zoom, O+D, F+C? • Occlusion, See inside? • Manipulation

Overview+Detail • Stoakley, “Worlds in Miniature” •

Volume Data 2 -D: • Voxel volume data • Fully sampled contents of 3 D objects • Voxel = 3 D pixel; tiny cube in a 3 D image • Volume = 3 D array of voxels • Examples: • MRI, Ca. T scan: » Measures tissue density at each point in space • Visible Human » slice and photograph • • The problem: 3 -D:

The Problem • E. g. the Visible Human • What’s inside?

Slicing • Visible Human Explorer • http: //www. cs. umd. edu/hcil/visible-human/vhp. mpg (north et al)

Overview+Detail Slice and Dice

3 D Cutting Plane • Ken Hinckley, UVA

Surface Reconstruction • Generate surface data from volume data • Iso-surfaces • Marching Cubes algorithm • • Look at cubes of 8 voxels Cube is on surface if: ? ? ? Generate polygons Smooth

Volume Rendering • Ray Casting • Like x-ray • Accumulate color & opacity along rays • “Transfer functions” • Splatting • Like projection • Reverse of ray-casting • Calculate each voxel’s contribution to image

Interactive Volume Rendering • Kniss, “Interactive volume rendering with direct manipulation” •

Transparency: X-Ray Vision Surface Volume http: //www. uke. uni-hamburg. de/institute/imdm/idv/vm 3 dn/io_xray_combined. en. html http: //graphics. stanford. edu/software/volpack/movies/vp_movies. html

Combining it all together • Voxel-Man • Hamburg University • http: //www. uke. uni-hamburg. de/institute/imdm/idv/vm 3 dn/io_thorax. en. html

3 -D volume data: Digital Video • 3 D: Stack 2 D video frames time y x

Slicing Digital Video Full overview: time zoom • Red’s Nightmare video in VHE • http: //vtopus. cs. vt. edu/~north/infoviz/Reds. Nightmare. mpg motion Scene change Pan left still credits