Add Spherical Law Of Cosines method

[vanderlee]

Spherical Law Of Cosines is commonly used instead of Haversine due to better performance and very close results. Generally, if you need higher accuracy than SLOC, Haversine is probably too inaccurate as well.

See here for an explaination of the quality aspect:
http://gis.stackexchange.com/questions/4906/why-is-law-of-cosines-more-preferable-than-haversine-when-calculating-distance-b

See here for documentation:
https://en.wikipedia.org/wiki/Spherical_law_of_cosines

If you want, I have PHP code for it, but it's pretty trivial to implement yourself.

[vanderlee]

Is this project still active?
If you need, I can provide some code for SLOC myself as I already have working PHP code, but compiling is a bit problematic.

[derickr]

Sorry, I never saw any notifications about this. I use this extension daily, but it hasn't gotten much attention as it "just works". If you can provide the formula, we can see whether we can add this of course!

[vanderlee]

Hi,

This is my SLOC code (using radians):
Note that SLOC is only correct when not crossing the 180 meridian.

function cosineRad($latFrom, $lngFrom, $latTo, $lngTo) {
	return acos((sin($latFrom) * sin($latTo)) + (cos($latFrom) * cos($latTo) * cos($lngTo - $lngFrom))) * EARTH_RADIUS;    
}

I don't remember if you already had the equirectangular (see http://www.movable-type.co.uk/scripts/latlong.html) algorithm, but here it is also:

function cosineRad($latFrom, $lngFrom, $latTo, $lngTo) {
	return acos((sin($latFrom) * sin($latTo)) + (cos($latFrom) * cos($latTo) * cos($lngTo - $lngFrom))) * EARTH_RADIUS;    
}

EARTH_RADIUS is the radius in. I used 6371 for testing with kilometers.