Calculate a convex hull - The QuickHull algorithm

Trivial Implementation at Fri, 06 May 2011 23:04:46 +0200

Trivial Implementation — Fri, 06 May 2011 21:04:46 +0000

In compliance with GPL3, here's my published code:


getHullPoints();
	
	echo "Updating " .  $region['name'] . "...\n";
	
	$polygon = mysql_real_escape_string(serialize($region['polygon']) );
	mysql_query('UPDATE regions ' .
		'SET polygon = \'' . $polygon . '\' ' .
		'WHERE id = ' . $region['id']
	);
	
	echo 'Polygon is ' . strlen($polygon) . ' characters.'; 
	
	if (strlen($polygon) > $max) {
		$max = strlen($polygon);
		$max_name = $region['name'];
	}
	
}

mysql_close($cn);

echo "Largest polygon is " . $max_name . " at " . $max . " characters.\n";

exit;

Barry Cornelius at Sun, 30 Jan 2011 19:31:52 +0100

Barry Cornelius — Sun, 30 Jan 2011 18:31:52 +0000

I wanted KML files giving the outline of UK postcode areas (e.g., DH). Surprisingly, I couldn't find these on the web. However, you can get from the Ordnance Survey/Royal Mail, the coordinates of the centre of each postcode (e.g., DH1 3LE). I used your code to generate some points giving an outline of a postcode area and produced some KML from these points. I specifically needed it for a web site I have for displaying future running races in North East England, as shown at http://www.northeastraces.com/running/races/explain/pcaYO?arg=pcaYO. However, I thought I might as well do the rest of the UK at the same time as shown at http://www.northeastraces.com/runningstatic/pcas/. Thanks.

Jason Judge at Sun, 30 Jan 2011 02:16:21 +0100

Jason Judge — Sun, 30 Jan 2011 01:16:21 +0000

Thanks! Just what I was looking for to create polygons around UK postcodes. I have up to 1.7 million points to process at any time, so will be looking for a way to apply this algorithm to a series of database queries rather than trying to pull all points into memory in one go. The diagrams are great in helping to understand how it all works.