Comments on: Calculating The Bearing And Compass Rose Direction Between Two Latitude / Longitude Coordinates In PHP

By: Jonathan

Jonathan — Mon, 24 Jan 2011 20:39:22 +0000

@Dan. Agreed about tendency to cast clockwise but your fix is going the wrong ‘direction’ ?

On a 8 point compass, I want each of the 8 directions to cover a 360/8=45deg sector but I MAY want the 45deg sector for North, as a good example, starting at -22.5deg to +22.5deg, rather than 0 to 45deg? For a 16 point compass the sectors are 22.5 degs so the offset is -11.25 to +11.25deg.

$tmp = floor(($bearing – 11.25) / 22.5);

By: Adam

Adam — Fri, 19 Feb 2010 16:31:13 +0000

AMAZING! I’ve modified one of your queries to add a calculated bearing field to query results. So I pass the lat/lon of an origin point into the query and all of the locations in the db come back with an extra bearing field (holding the calculated bearing between the origin point and each record’s lat/lon).

Thank you Thank you!

By: Dan Richards

Dan Richards — Mon, 15 Feb 2010 17:09:48 +0000

The following mod to the getCompassDirection function will correct the problem “this function will tend to cast directions clockwise around the compass rose”:

$tmp = floor(($bearing + 12.25) / 22.5);

By: Garth Powell

Garth Powell — Mon, 04 Jan 2010 16:48:34 +0000

Okay, when I get to that point (which will be soon, I’ll (most likely) send something from your wish list…in looking at the books and media, you’re nicely diverse in what interests you…some of them I may want to get to read!

GAP

By: Doug Vanderweide

Doug Vanderweide — Thu, 24 Dec 2009 15:39:46 +0000

@Garth: I am happy to assist you with your specific implementation in return for a purchase from my Amazon wish list. Click the "Need More Help Or Want To Say Thanks?" link at the top of the page for more info.

By: Garth Powell

Garth Powell — Thu, 24 Dec 2009 14:32:19 +0000

Did a “cut and paste” on the bearings formula above (thank you)…took out the “$bearing” part, left the “=”. In place of “$lat2″ and so on, I put the specific cell for the specific information. Pressed “enter” and my 2003 version of Excel didn’t like or know what to do with “% 360;”. What am I missing here? Do I need to leave the “$” in all the time? Will do so when I run a number of these as the starting point will be a constant for a given set and I also took out spaces in the formula…mistake on my part? Thanks, Garth

By: Doug Vanderweide

Doug Vanderweide — Fri, 11 Dec 2009 03:12:50 +0000

Thanks for the catch, Chris. I’ve corrected the post, demo and code. (PS: Love your Web site. British idioms amuse me to no end.)

By: Chris Rae

Chris Rae — Fri, 11 Dec 2009 02:32:55 +0000

This is amazingly handy - I converted your code into C# and integrated it into my app. Worked first time, after some considerable time I'd already spent trying to hack around myself (I remember trigonometry even worse than you claim to!). I think there's actually a mistake in your rhumb line bearing calculation. You write:

		if($dLon > 0) {
			$dLon = (2 * pi() - $dLon) * -1;
		}
		else {
			$dLon = 2 * pi() * $dLon;
		}

but the equivalent piece of code on movable type says:

 dLon = dLon>0 ? -(2*Math.PI-dLon) : (2*Math.PI+dLon);

The first option is equivalent, but in the second you are multiplying by dLon and the code at movable type is adding. I have to admit to not having the faintest idea which is correct, but I *think* it's the addition one.

By: Doug Vanderweide

Doug Vanderweide — Wed, 28 Oct 2009 14:45:09 +0000

@mustak: East is 90 degrees.

By: mustak

mustak — Wed, 28 Oct 2009 14:19:02 +0000

please tell me how to calculate east bearing from available co ordinates…