MapKit lines and polygons

I have a map and line (poly-line) on it. I'm trying to make a smooth polygon around this line. The problem I'm f开发者_JAVA百科acing is how to create that polygon look smooth with rounded ends. any suggestions/solutions? I've tried to draw another line over existing one with different thickness, but it doesn't work well with zooming...

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In MKOverlayPathView which is a superclass of MKPolylineView there is a property called lineCap. Set it to

kCGLineCapRound

check here: http://developer.apple.com/library/ios/#documentation/MapKit/Reference/MKOverlayPathView_class/Reference/Reference.html

Hope it helps.