# NAME

GIS::Distance - Calculate geographic distances.

# SYNOPSIS

```
use GIS::Distance;
my $gis = GIS::Distance->new();
$gis->formula( 'Polar' ); # Optional, default is Haversine.
# Or:
my $gis = GIS::Distance->new( 'Polar' );
my $distance = $gis->distance( $lat1,$lon1 => $lat2,$lon2 );
print $distance->meters();
```

# DESCRIPTION

This module calculates distances between geographic points on, at the moment, plant Earth. Various formulas are available that provide different levels of accuracy versus calculation speed tradeoffs.

All distances are returned as Class::Measure objects.

# METHODS

## distance

` my $distance = $gis->distance( $lat1,$lon1 => $lat2,$lon2 );`

Returns a Class::Measure::Length object for the distance between the two degree lats/lons. The distance is calculated using whatever formula the object is set to use.

# ATTRIBUTES

## formula

This is an object who's class inherits from GIS::Distance::Formula. This object is used to calculate distance. The formula may be specified as either a blessed object, or as a string, such as "Haversine" or any of the other formulas.

If you specify the formula as a string then a few different class names will be searched for. So, if you did:

` $gis->formula( 'Haversine' );`

Then this list of packages would automatically be looked for. The first one that exists will be created and used:

```
GIS::Distance::Formula::Haversine::Fast
GIS::Distance::Formula::Haversine
Haversine
```

If you are using your own custom formula class make sure it applies the GIS::Distance::Formula role.

Note that a ::Fast version of the class will be looked for first. By default the ::Fast versions of the formulas, written in C, are not available and the pure perl ones will be used instead. If you would like the ::Fast formulas then install GIS::Distance::Fast and they will be automatically used.

# SEE ALSO

GIS::Distance::Fast - C implmentation of some of the formulas shipped with GIS::Distance. This greatly increases the speed at which distance calculations can be made.

# FORMULAS

GIS::Distance::Formula::Cosine

GIS::Distance::Formula::GeoEllipsoid

GIS::Distance::Formula::GreatCircle

GIS::Distance::Formula::Haversine

GIS::Distance::Formula::MathTrig

GIS::Distance::Formula::Vincenty

# TODO

Create a GIS::Coord class that represents a geographic coordinate. Then modify this module to accept input as either lat/lon pairs, or as GIS::Coord objects.

Create an extension to DBIx::Class with the same goal as Geo::Distance's closest() method.

Write a super accurate formula module called GIS::Distance::Geoid. Some very useful info is at http://en.wikipedia.org/wiki/Geoid.

# BUGS

Both the GIS::Distance::Formula::GreatCircle and GIS::Distance::Formula::Polar formulas are broken. Read their respective man pages for details.

# AUTHOR

Aran Clary Deltac <bluefeet@cpan.org>

# LICENSE

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.