Thursday, June 25, 2009

Tag cloud seeking harmony

I'm about to release the code for the tag cloud - here's a teaser of the code that each tag runs to seek harmony:

  internal void SeekHarmony(IEnumerable<Tag> valueCollection, double SIZE)
   double maxOccurance = OccuredCount + 0.1d;

   // how we scale the whole cloud, 4 would be exactly the size of the area
   // 3 would be slightlight larger and 5 would be smaller
   const double ATTRACTION_SCALE = Math.PI;
   // how much tags that have not cooccurred repel each other
   // ϕ (golden ratio) gives us a nice aesthic
   const double REPEL_RATIO = 1.618d;
   // how much tags that cooccurred attract each other
   // it must be greater than the repel rate or everything
   // will fly away from each other
   const double ATTRACT_RATIO = Math.E;

   // assume we don't need to be moved
   Point offset = new Point(0, 0);

   // work out where the best place in 2d space to be
   // would be given where all the other tags are
   foreach (Tag otherTag in valueCollection)
    // ignore ourself
    if (otherTag == this)

    // work out vector bewteen us and the other tag
    Polar vector = Trigonometry.CartesianToPolar(this.Point, otherTag.Point);

    // how far apart?
    double distance = vector.Magnitude;

    // how much they repel by default
    double desiredDistance = maxOccurance * REPEL_RATIO;
    // did we co-occur with the other tag?
    int cooccurred = this[otherTag];
    if (cooccurred != 0)
     // we want to closer to the other tag based on frequency
     desiredDistance /= (cooccurred * (ATTRACTION_SCALE / ATTRACT_RATIO));

    // scale the distance based on the play area and how important
    // the other tag is compared to all the tags we co-occurred with
    distance = SIZE * (desiredDistance / (ATTRACTION_SCALE * maxOccurance));
    distance = (vector.Magnitude - distance); // towards not away

    // work out what vector needs to be applied to our
    // current position to move us closer
    Polar desiredVector = new Polar(vector.Direction, distance);
    Point offsetPoint = Trigonometry.PolarToCartesian(desiredVector);

    // accumlate all the proposed changes
    offset.X += offsetPoint.X;
    offset.Y -= offsetPoint.Y;

   // update our new position, (scaled to fit within play area)
   // and also scaled to allow gradual movement
   double rateOfChange = SIZE / ATTRACTION_SCALE;
   point.X += offset.X / rateOfChange;
   point.Y += offset.Y / rateOfChange;
hopefully I will post all the code and zip file tomorrow..

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