1. CS 526: Computer Graphics II University of Illinois at Chicago An Introduction to Glyphs Allan Spale Spring 2004

2. CS 526: Computer Graphics II University of Illinois at Chicago Description Visual object that represents data –Geometry or image Changes its appearance based on current data values –Size, orientation, color, location, etc. Almost like an “icon” but not a “symbol” –Icon: “A sign whose form represents its meaning.” –Symbol: “Something that stands for or suggests something else…”

3. CS 526: Computer Graphics II University of Illinois at Chicago Simple Example Instead of using letter grades, try using faces The glyph is actually the “mouth” of the “smiley face” and not all the parts of the face A B C D E

4. CS 526: Computer Graphics II University of Illinois at Chicago Classification by Delmarcelle and Hesselink Based on a framework for flow visualization Elementary icons –Glyph type used to represent information Local icons –Glyph type with additional local information Global icons –Glyph type that encompasses structure of an entire dataset

5. CS 526: Computer Graphics II University of Illinois at Chicago Examples of Elementary Icons Only one property of the glyph is variable –Orientation, size, stretch/shrink, etc. Examples –N-dimensional geometry (line, triangle, cone, etc.)

6. CS 526: Computer Graphics II University of Illinois at Chicago Examples of Local Icons Multiple glyph properties are variable –Color and orientation; size and color; etc. Examples –Colored hedgehogs; colored, scaled, and orientated tensors

7. CS 526: Computer Graphics II University of Illinois at Chicago Examples of Global Icons Dataset represented by one glyph –Isosurfaces, non-traditional complex glyphs Examples –Medical tissues; facial expression for financial data

8. CS 526: Computer Graphics II University of Illinois at Chicago Problems Using 3-D –Viewing a 3-D glyph on a 2-D surface can make glyph orientation and position difficult to determine Frequency –Clutter can obstruct individual glyphs Scaling –Creates “nonlinear differences in appearance” –Consult Tufte’s Visual Display of Quantitative Information

9. CS 526: Computer Graphics II University of Illinois at Chicago Applications Seismoglyphs –Originated from his thesis on Wiggleview Atul Nayak –Displays 3-D earthquake data over time –Glyph retains a compact form

10. CS 526: Computer Graphics II University of Illinois at Chicago Applications Uncertainty visualization –“Procedural Annotation of Uncertain Information” Andrej Cedilnik and Penny Rheingans –How to visualize data that is missing or uncertain Use glyphs that have a distortion/noise attribute Must be careful that the glyph retains its structure and does not hinder understanding

11. CS 526: Computer Graphics II University of Illinois at Chicago Using Glyphs in VTK: Example from Text vtkDataSetvtkPolyData vtkGlyph3D vtkPolyData Input Source vtkDataSet (input) –Abstract class for dataset objects Considers geometry, topology, and attributes Attribute data is either point or cell –Data used as input to the glyph

12. CS 526: Computer Graphics II University of Illinois at Chicago Using Glyphs in VTK: Example from Text vtkPolyData (source) –Concrete class of vtkDataSet –Supports cell types including vtkVertex, and vtkPolygon –Has some data manipulation and traversal methods –Delivers geometry of the glyph to the class vtkGlyph3D vtkDataSetvtkPolyData vtkGlyph3D vtkPolyData Input Source

13. CS 526: Computer Graphics II University of Illinois at Chicago Using Glyphs in VTK: Example from Text vtkGlyph3D –Inputs to class vtkDataSet = data to visualize vtkPolyData = glyph geometry –Decisions to make Scaling, orientation, etc. Recall glyph problems –Note the warnings in the API vtkDataSetvtkPolyData vtkGlyph3D vtkPolyData Input Source

14. CS 526: Computer Graphics II University of Illinois at Chicago Using Glyphs in VTK: Example from Text vtkPolyData (output) –Glyph characteristics in vtkGlyph3D and vtkPolyData (input) –Glyph characteristics influenced by input data of vtkDataSet vtkDataSetvtkPolyData vtkGlyph3D vtkPolyData Input Source

15. CS 526: Computer Graphics II University of Illinois at Chicago Demo Using Glyphs in VTK: thrshldV.py Adapted from Tcl script in VTK text on page 193 to Python. –(Figure 6-43) “Visualizing blood flow in human carotid arteries. Cone glyphs indicate the flow direction and magnitude.” vtkStructuredPointReader vtkThresholdPoints vtkMaskPoints vtkGlyph3D vtkPolyDataMapper vtkConeSource

16. CS 526: Computer Graphics II University of Illinois at Chicago Thanks for listening

17. CS 526: Computer Graphics II University of Illinois at Chicago Bibliography Internet –Definitions of “symbol” and “icon” are from Merriam-Webster Online at: http://www.m-w.comhttp://www.m-w.com –Wiggleview by Atul Nayak http://www.evl.uic.edu/cavern/agave/wiggleview/; includes link to seismoglyphshttp://www.evl.uic.edu/cavern/agave/wiggleview/ –Journal article: “Procedural Annotation of Uncertain Information” by Andrej Cedilnik and Penny Rheingans; proceedings of IEEE Visualization 2000. –Image (cone swirl) from Andy Johnson’s CS 526 Lecture Notes –VTK API Documentation Book –VTK Text: OO Approach to 3-D Graphics Most images were from the text Most content was taken from chapter 6 and glossary

18. CS 526: Computer Graphics II University of Illinois at Chicago Questions and Comments