Tuesday, September 18, 2012

Graphic animations

In my post Baker 2012, I left the analysis until a future posting, hoping that there would be some comments with analyses.  The expected comments came in (both on the blog and by e-mail), and I discovered a problem with the description of the incident: the animated graphical display was misleading.

An animated graphical display is better than the traditional static display for several reasons.  First, it shows much more clearly what happened throughout the incident.  If you’ve ever analyzed a US Appeal, ISAF Case, or match- or team-race Call, you’ve probably been frustrated by the fact that a key part of the rules discussion hinges on a circumstance that happened between positions n and n+1.  Because the critical fact isn’t shown, we are forced to guess what happened, and when.  Second, the animated graphical display moves the boats in realistic ways, whereas the static display may actually put the boats in positions that it’s impossible to get into, in subtle ways that make a difference in how the scenario plays out.  In fact, even if you use Boat Scenario (http://boats.sf.net) or TSS (http://tss.peronneau.net) only to build static diagrams, I urge you to run your diagrams through the animation feature, just to pick up the places where, if your static diagrams were true, boats would cross through each other or jump from place to place without changing course. 

But an animated graphic can also misrepresent the scenario in a way that the static display (or an on-the-water umpire’s view) doesn’t do, and that’s the case with the graphic in ‘Baker 2012’.  In that animation, when A luffs X, X clearly leaves the zone, so she loses her rights to mark-room.  But when she jibes back and enters the zone, she’s still clear ahead of the third boat, B.  You can see this clearly if you look at the static display that remains for a second or two after the animation concludes – at position 5, a line drawn across X’s stern crosses at least ½ boatlength in front of B.

My original description of the scenario stated that X was clear ahead of B when she re-entered the zone, but somehow that sentence got dropped when I was reformatting the blog.  My apologies.

In any case, please take a second look at the Baker 2012 post and tell me now what you think.

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