FindMyNearest

FindMyNearest is a PHP class for working with UK postcodes, and 
in particular for calculating the distance between two postcodes.
FindMyNearest supports several alternative data sources through
drivers. Currently data can be got from a delimited text file, a
mysql database or through the web API at www.uk-postcodes.com

FindMyNearest is generally not too fussy about the formatting of 
postcodes. It accepts any case, spaces between parts or not and
partial postcodes. It even corrects the letter O at the beginning
of an inward part, changing it to the nubmer 0.

If the backend datasource contains location data for 
partial postcodes these are used if an exact match can't be found.

Synopsis
========

require 'FindMyNearest.php';

$fmn = FindMyNearest::factory('textfile', array('datafile' => 'postcodes.txt'));

if (! $fmn->loaddata()) {
  echo "Error loading data: " . $fmn->lasterror() . "\n";
  exit;
}

$goodcode = $fmn->validcode('SW1A 1AA');    // Check if we know about a code

$distance = $fmn->calc_distance('SW1A 1AA', 'CV32 5HZ'); // calculate distance

if ($distance === false) {
  echo "The was an error " . $fmn->lasterror();
}

Methods
=======

factory(string $driver, array $params)

  Create a new instance. $driver is currently one of 'textfile', 'mysql', 
  'uk_postcodes', 'ukgeocode', 'geopostcode' or 'openlylocal'. Valid values
  for $params depend on the driver chosen.
  
loaddata()

  Initialise the connection to the back end. This must always be called
  before any functions needing to look up postcodes can be called.
  
set_inoutsep(string $sep)

  Sets the value of the separator between outward (SW1A) and inward (1AA) 
  parts of the postcode data. The default depends on the driver. It is a
  single space usually, but an empty string for uk_postcodes. The use of 
  an empty string is not recommended if your data also includes means or
  midpoints for districts and sectors, because this can be ambiguous. Eg
  'B11' could be either the district B11 or the sector B1 1.

use_wgs84()

  Indicates that the geo data is in wgs84 (latitude and longitude) format
  Note that when using the mysql driver if you do not specify the sql 
  parameter in the paramaters passed to factory() and you are using wgs84 you
  must call use_wgs84() *before* calling loaddata. This is because the default
  SQL is dependent on the co-ordinate scheme being used.
  
use_osgb36()

  Indicates that the geo data is in osgb36 (British national grid) format.
  This is the default.

  Note that the uk_postcodes driver (which uses http://www.uk-postcodes.com)
  can provide data in either wgs84 or osgb36. The latter makes distance
  calculations less demanding

validcode(string $postcode [, bool $exactmatch])

  Tests if a postcode is valid and known in the database. Returns the found
  code on success, false on failure. 

  If the full code is not found, checks will be made for matches by sector
  (SW1A 1), district (SW1A) and area (SW1). The return value is the best 
  match.
  
  If $exactmatch is true (defaults to false), matches only if the $postcode
  is known (after normalising $postcode).

set_grain(int $grain)

  Sets the smallest unit that will be checked for by validcode()
    1: Area only: SW 
    2: District: SW1A
    3: Sector: SW1A 1
    4: Unit: SW1A 1AA

getgeodata(string $postcode)
  
  Returns an array containing the location of the postcode. The elements are
  (eastings, northings) for osgb36 or (latitude, longitude) for wgs84

splitpostcode(string $postcode)
  
  Takes a postcode or partial postcode and attempts to split it into 
  component parts. Returns an array:

      [0] => Area,
      [1] => District
      [2] => Sector
      [3] => Unit

    eg, for SW1A 1AA
      [0] => SW
      [1] => 1A
      [2] => 1
      [3] => AA
  
  Returns false on failure
  
samepostcode(string $postcode1, string $postcode2)
  Checks if $postcode1 is the same postcode as $postcode2
  Returns true if the same, false otherwise

normalise ($postcode) 
  Returns a normalised version of $postcode, taking account of the current
  setting of $inoutsep
  
calc_distance (string $fromcode, string $tocode[, array $options])
  
  calculate the distance between $fromcode and $tocode. 
  $options is an optional array:
    unit => 'miles'|'km'    The unit to return the distance in (default miles)
    decimal => int  The number of decimal places (defalt 0)

  Like validcode(), if an exact match isn't available calc_distance will
  match on sector, district or area.
  
  Returns false on failure. 
  ***********************************************************************
  *NB* 0 is a valid, good response indicating a distance of 0km or 0miles
  Be sure to test for false (eg if($d === false)
  ************************************************************************

lasterror()
  
  returns the last error message generated


Drivers
=======

textfile
========
The textfile driver stores postcode data in a simple text file. The following 
parameters are available:

   datafile: location of the datafile
   fieldsep: field separator used in the datafile. Default is "\t" (tab)

Data files should contain three fields, either

postcode    latitude    longitude
or 
postcode    eastings    northings

The textfile driver is useful for simple installations requiring data
only down to sector level. It is not recommended if you have unit level
data, unless it is for a small area only, as there are 17 million postcodes
in Great Britain

mysql
=====
The mysql driver stores data in a mysql database. Valid parameters are

    host: mysql host to connect to
    user: user name for mysql connection
    pass: password for mysql connection
    db:   database to use
    sql:  the SQL statement to execute. This should take a single substitution,
          %s, which is replaced by the postcode being searched. It should return 
          two fields, eastings and northings or latitude and logtitude. Defaults are
          "SELECT lat,long FROM postcodes WHERE postcode = '%s'" for wgs84 and
          "SELECT east,north FROM postcodes WHERE postcode = '%s' for osgb36


uk_postcodes
============
The uk_postcodes driver uses the API at http://www.uk-postcodes.com to retrieve 
data. It caches data in a local file to minimize the load on the remote server.
Valid parameters are:

    cachefile: path to file for cache. Must be readable and writeable by server
    cachettl: time to live in seconds for cache entries (default 604800, 1 week)

The uk_postcodes driver only handles full postcodes. Consequently the behaviour of
validcode() is slightly different, in that it will not check for matches at sector 
level or below.

ukgeocode
=========
The ukgeocode driver uses the API at http://maxmanders.co.uk/ukgeocode/ to retrieve 
data. It caches data in a local file to minimize the load on the remote server.
Valid parameters are:

    cachefile: path to file for cache. Must be readable and writeable by server
    cachettl: time to live in seconds for cache entries (default 604800, 1 week)

The ukgeocode driver only handles full postcodes. Consequently the behaviour of
validcode() is slightly different, in that it will not check for matches at sector 
level or below.

ukgeocode uses wgs84. The driver will set this - there is no need to call use_wgs84

openlylocal
===========
The openlylocal driver uses the API at http://www.openlylocal.com/ to retrieve 
data. It caches data in a local file to minimize the load on the remote server.
Valid parameters are:

    cachefile: path to file for cache. Must be readable and writeable by server
    cachettl: time to live in seconds for cache entries (default 604800, 1 week)

The openlylocal driver only handles full postcodes. Consequently the behaviour of
validcode() is slightly different, in that it will not check for matches at sector 
level or below.

openlylocal uses wgs84. The driver will set this - there is no need to call use_wgs84

geopostcode
===========
The geopostcode driver uses the API at http://www.geopostcode.org.uk to retrieve 
data. It caches data in a local file to minimize the load on the remote server.
Valid parameters are:

    cachefile: path to file for cache. Must be readable and writeable by server
    cachettl: time to live in seconds for cache entries (default 604800, 1 week)

Writing drivers
===============
Drivers are classes that extend FindMyNearest. A driver provides a class named 
FindMyNearest_<driver> and is stored in the file drivers/<driver>.php, where <driver>
is the driver's name.

A driver should provide a method named FindMyNearest_<driver>, which takes as an 
argument an associative array of options. It should return true, or on error return
false.

Drivers should provide the following override methods:

loaddata()
  Takes no paramaters. Return true on success. On failure, returns false and sets
  $this->lasterr. Does whatever needs to be done to initialise the backend connection
  
getgeodata($postcode)
  Return an array of either (lat, long) or (east, north) coordinates for the supplied
  postcode
  
_postcodeknown($postcode)
  Return true if $postcode exists in the backend, false otherwise
  
dumpdata()
  Does something useful for debugging. Exactly what is useful is likely to depend
  on the driver
  
When writing drivers to access web services, it may be useful to include WebServices.php
and then write your class to extend FindMyNearest_WebServices. This provides a number of
useful functions for accessing web services and maintaining a cache of data.