Re: Re: Google Maps Distance Between UK Postcodes

At 8:31 AM -0700 9/11/08, mike wrote:

On Thu, Sep 11, 2008 at 8:17 AM, tedd <tedd.sperling@gmail.com> wrote:

Considering that my other profession is Geophysicist, I'm kind of up on those sort of things. The Earth is an oblate spheroid and the computation to include the curvature of the earth would be a bit more involved.

what do you think of the code i mentioned earlier? $distance = number_format(ceil(69*rad2deg(acos(sin(deg2rad($ulat)) * sin(deg2rad($vlat)) + cos(deg2rad($ulat)) * cos(deg2rad($vlat)) * cos(deg2rad($ulong - $vlong)))))); where: $ulat = latitude of user #1 $ulong = longitude of user #1 $vlat = latitude of user #2 $vlong = longitude of user #2 I took the very popular mysql query (at the time) that supposedly works with a sphere and mapped it to php functions and it has appeared to work very well. I have only tested with US zip codes, but the concept should be the same as long as lat/long are centered properly.

I dunno. But I do know that knowing the latitude and longitude of two points on the surface of the Earth and then trying to calculate the actual distance between each is not a trivial task Take a look at: http://en.wikipedia.org/wiki/Latitude#Degree_length In that table you can see that for every degree north-south there is a change -- likewise, for every degree east-west AND those changes are not equal. This has been a problem for map makers for a long time. I remember surveying ancient playas (i.e., lake-beds) in the Mohave desert where my rod man would travel away and I would see his boots disappear beneath the curvature of the Earth. Now, what's the distance between me and my rod man? Is it the distance I see in my survey instrument or the distance of my rod chain? One is a straight line while the other isn't -- which is the correct one? Cheers, tedd -- ------- http://sperling.com http://ancientstones.com http://earthstones.com