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revision 1.48 by jvk, Mon Feb 10 13:34:08 2003 UTC revision 1.49 by jvk, Mon Feb 10 17:49:33 2003 UTC
# Line 265  Buoys Line 265  Buoys
265    
266  - can smoothly adjust buoy size and location  - can smoothly adjust buoy size and location
267    
268    We draw the link targets as buoys around the focus.
269    
270    Layout requirements:
271    
272        - buoys should not be placed over the focus
273    
274        - buoys should be placed close to their anchors
275    
276        - buoys anchored closer to the focus should be larger
277    
278        - the layout should animate continuously when the focus moves
279    
280    Furthermore,
281  It is important to maintain orientation locally (i.e., left/right  It is important to maintain orientation locally (i.e., left/right
282  direction of links, etc.) but the space need not be globally  direction of links, etc.) but the space need not be globally
283  euclidian. This matches the way the brain understands space  euclidian. This matches the way the brain understands space
284  as globally distorted, segmented, locally Euclidian views.  as globally distorted, segmented, locally Euclidian views.
285  Some refs (should search for more/better):  Some refs (should search for more/better):
286  http://acad88.sahs.uth.tmc.edu/research/publications/iccs2001spatial.pdf  http://acad88.sahs.uth.tmc.edu/research/publications/iccs2001spatial.pdf
287    [#wang01mindsviews]_
288  http://citeseer.nj.nec.com/hunt99orientation.html  http://citeseer.nj.nec.com/hunt99orientation.html
289    
290  Because of this, each link has a specific left-right orientation ...  That is, going in one direction should result in arriving from
291    the opposite direction.
292    
293  Geometry:  Because of this, each link has a specific left-right orientation
294    so that a right-end buoy is drawn on the right side of the view
295    and a left-end buoy on the left side.
296    
297    - buoys on a circle  More than two opposing directions could also be used, but
298    
299          - matches fisheye shape          - it is not required for maintaining the sense of direction
         - other reasons?  
         - why not simply straight lines on left/right sides?  
300    
301    - projected from a constant point (on left/right) through the          - it would limit the layout of a large number of buoys
     anchor to right/left side of the circle  
302    
303          - projections are easy to track for humans          - there is usually no meaningful global 2D layout of a network
304              of nodes; in our application, the structure has simply
305              directed links, visualized as the left-right direction.
306    
307    - final positions may be adjusted to prevent too much overlap  The horizontal orientation is more natural than, e.g., vertial, because
308    the visual field is wider than it is tall
309    (exemplified by the usual screen aspect ratios of 4:3 and 16:9)
310    leaving more space at the left and right sides than on the top and bottom.
311    XXX: left and right hand???
312    
313          - how does this interact with the perception of the projection?  We choose the geometry as follows:
314    
315      - buoys are placed on a circle centered at the focus and diameter
316        little less than the screen height
317    
318    - buoys far from the focus are drawn at the anchor instead          - buoys equally close to the focus, matching the fisheye focus shape
319    
320            - provides more space for the buoys than, e.g., a straight line
321              (a circle arc is longer)
322    
323      - buoys anchored outside the buoy-circle are drawn near the anchor instead,
324        to prevent awkward view-cutting long lines and to yield more space
325        for the layout of buoys anchored closer to the focus
326    
327      - the position on the circle is obtained by projecting from a constant
328        point (on left/right) through the anchor to right/left side of the circle
329    
330            - buoys placed close to the anchor
331    
332            - such line projections are easy to track for humans,
333              because it is analogous to 3d perspective
334    
335      - final positions may need be adjusted to prevent too much overlap
336    
337            - how does this interact with the perception of the projection?
338    
339    - buoy scale    - buoy scale is relative to the anchor's distance from the circle
340            
341    The above design produces good results and is very simple if not
342    the simplest way to meet the layout requirements.
343    
         - buoys closer to the focus should be larger  
         - scale is relative to the anchor's distance from the circle  
344    
345  Break lines  Break lines
346  -----------  -----------

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