CompGeomIntro

# E p 2 2 for all p q r p 3 such that r p q 3 if

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Unformatted text preview: Input: a set P of points in IR2 Output: C H(P ) 1. E ←P 2 2. for all (p, q , r) ∈ P 3 such that r ∈ {p, q } / 3. if C C W (p, q , r ) ≤ 0 4. then remove (p, q ) from E 5. Write the remaining edges of E into L in counterclockwise order 6. Return L CONVEX HULL - Divide & Conquer ding p itself, and the p oints to the right of p, by comparing x-coordinates. Recurs the convex hulls of L and R. Finally, merge the two convex hulls into the ﬁnal outp erge step requires a little explanation. We start by connecting the two hulls with a ✦ een the re tmost po in x the hull of L an Spl t P t to t o o se hu b etwCo mputighme dian int of -co ordinate withdthe leiftmosinp ointwf the ts ll e ✦oints p and q , resp ectively. (Yes, it’s the same p.) Actually, let’s add two cop p Compute Left an d Right Hulls recursively ent pq and call them bridges. Since p and q can ‘see’ each other, this creates a so -shap ed rglegon, which isHunlsx except p ossibly at the endp oints oﬀ the bridges. ✦...
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