Implement Great Circle Algorithm

Question

Below is a formula (Great Circle algorithm) that I want to be translated into PHP. I would really appreciate if someone would help me with that?

The input is to different sets of coordinates, e.g:

Place 1 Lat: 59.389057
Place 1 Long: 17.937422

Place 2 Lat: 59.388914
Place 2 Long: 17.920441

The wanted output is the distance between place 1 and place 2.

distance = ((115.1666667 * (lat2-lat1)) ^ 2 + (115.1666667 * (lng2 - lng1) * cos(lat2 / 57.3)) ^ 2) ^ .5

My try:

$distance = pow(((115.1666667 * ($lat2 - $lat1)), 2) + (115.1666667 * pow(($lng2 - $lng1) * cos($lat2 / 57.3)), 2)), 0.5)

Why is your try poor? How could you improve it? How can you test it to show that it is working? Where do you hit the roadblock to translate the formula? What are the input values? What are the expected output values? [delref](http://stackoverflow.com/q/14091549/367456) — hakre, Dec 30 '12 at 15:28
This is a pretty good example of "temporary variables make things easier to read". — DCoder, Dec 30 '12 at 15:52

score 3 · Accepted Answer · answered Dec 30 '12 at 16:04

3

As DCoder writes in the comments, temporary variables make things easier to read:

$latD = (691 / 6) * ($lat2 - $lat1);
$lngD = (691 / 6) * ($lng2 - $lng1) * cos($lat2 / 57.3);

$distance = sqrt( $latD * $latD + $lngD * $lngD );

answered Dec 30 '12 at 16:04

Ilmari Karonen

1

Ps. For a more accurate formula, see http://en.wikipedia.org/wiki/Haversine_formula – Ilmari Karonen Dec 30 '12 at 16:11

Shoe · Answer 2 · 2012-12-30T15:59:22.767

1

Here's the corrected code:

$distance = pow((pow((115.1666667 * ($lat2 - $lat1)), 2) + pow((115.1666667 * ($lng2 - $lng1) * cos($lat2 / 57.3)), 2)), 0.5);

edited Dec 30 '12 at 15:59

answered Dec 30 '12 at 15:30

Shoe

Thanks for the answer! There's somethin g wrong with it cause I get an error: syntax error, unexpected ',' ? – holyredbeard Dec 30 '12 at 15:41
In case anyone else is wondering about this as I was - the return value is in kilometres. – Chris Rae Sep 11 '13 at 11:59

2 Answers2