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Helper class for Yii to build SQL queries that calculate the geographical distance from a point (in miles) - can be used with models that have latitude/longitude coordinates to filter by (and/or compute) the distance from a point.
<?php
/**
* @version 1.0
* @author Rasmus Schultz <http://blog.mindplay.dk/>
* @license LGPL3 <http://www.gnu.org/licenses/lgpl-3.0.txt>
*/
/**
* Helper-class to build SQL queries that calculate the geographical distance
* from a point (in miles) - can be used with models that have latitude/longitude
* coordinates to filter by (and/or compute) the distance from a point.
*
* The recommended approach, is to add one or more scope methods to your models,
* so that the exact behavior is built into the model and easy to reuse - here
* is an example/template scope method, using all of the key features:
*
* public function near($lat, $long, $dist = 10)
* {
* $helper = new GDistanceHelper('t.geo_lat', 't.geo_long');
*
* $c = $this->getDbCriteria();
*
* // select all columns from the root table:
* $c->mergeWith(array('select' => 't.*'));
*
* // optimize the query by first filtering results by bounds:
* $c->mergeWith($helper->getBoundsCriteria($lat, $long, $dist));
*
* // filter the results further, by exact max. distance:
* $c->mergeWith($helper->getMaxRadiusCriteria($lat, $long, $dist));
*
* // compute the radius (as a column) and bind to $distance:
* $c->mergeWith($helper->getRadiusCriteria($lat, $long, $dist));
*
* // order results by distance:
* $c->mergeWith(array('order' => $helper->alias));
*
* return $this;
* }
*
*/
class GDistanceHelper
{
/** @var string latitude column name/expression */
public $lat_expr;
/** @var string longitude column name/expression */
public $long_expr;
/** @var string default/base alias */
public $alias;
/**
* @param string $lat_col latitude column name/expression
* @param string $long_col longitude column name/expression
* @param string $alias alias to use (by default; can be overridden in methods)
*/
public function __construct($lat_col, $long_col, $alias = 'distance')
{
$this->lat_expr = $lat_col;
$this->long_expr = $long_col;
$this->alias = $alias;
}
/**
* Compute min/max latitude and longitude ranges for a
* circle with the given radius, at the given coordinates.
*
* @param $lat
* @param $long
* @param $distance
* @param &$lat_min
* @param &$lat_max
* @param &$long_min
* @param &$long_max
*/
public static function getBounds(
$lat,
$long,
$distance,
// return values:
&$lat_min,
&$lat_max,
&$long_min,
&$long_max
) {
$long_min = $long - $distance / abs(cos(deg2rad($lat)) * 69);
$long_max = $long + $distance / abs(cos(deg2rad($lat)) * 69);
$lat_min = $lat - ($distance / 69);
$lat_max = $lat + ($distance / 69);
}
/**
* Create an SQL expression to compute the distance from
* a given latitude and longitude.
*
* The origin (the center from which to calculate the distance) must
* be given as a pair of latitude/longitude placeholder names, which
* should be bound to actual values in your query.
*
* The destination latitude/longitude columns to use in the expression,
* must be given as a pair of column names/expressions.
*
* @param string $orig_lat origin latitude placeholder name
* @param string $orig_long orgin longitude placeholder name
* @param string $dest_lat destination latitude column name/expression
* @param string $dest_long destination longitude column name/expression
*
* @return string
*/
public static function getExpression($orig_lat, $orig_long, $dest_lat, $dest_long)
{
return "3956 * 2 * ASIN("
. "SQRT("
. "POWER(SIN((:{$orig_lat} - ABS({$dest_lat})) * PI() / 2 / 180), 2)"
. " + COS(:{$orig_lat} * PI() / 180) * COS(ABS({$dest_lat}) * PI() / 180)"
. " * POWER(SIN((:{$orig_long} - {$dest_long}) * PI() / 2 / 180), 2)))";
}
/**
* Compute the distance between two pair of geographical coordinates.
*
* This is an alternative to {@see getRadiusCriteria()} which can be used to
* compute the distance at the DBMS level - you may prefer to compute the
* distance on demand using this method instead, for example, if you do not
* wish to introduce a transient property to your model.
*
* @see getRadiusCriteria()
*
* @param float $orig_lat latitude of point of origin
* @param float $orig_long longitude of point of origin
* @param float $dest_lat latitude of destination point
* @param float $dest_long longitude of destination point
*
* @return float distance (in miles)
*/
public static function getDistance($orig_lat, $orig_long, $dest_lat, $dest_long)
{
return 3956 * 2 * asin(
sqrt(
pow(sin(($orig_lat - abs($dest_lat)) * M_PI_2 / 180), 2)
+ cos($orig_lat * M_PI / 180) * cos(abs($dest_lat) * M_PI / 180)
* pow(sin(($orig_long - $dest_long) * M_PI_2 / 180), 2)
)
);
}
/**
* Build criteria matching records with coordinates falling within
* the boundary of a rectangle at the given coordinates.
*
* @param float $lat center latitude of bounding rectangle
* @param float $long center longitude of bounding rectangle
* @param float $distance distance to edge of bounding rectangle (in miles)
* @param string|null $alias alias to use in criteria conditions
*
* @return CDbCriteria
*/
public function getBoundsCriteria($lat, $long, $distance, $alias = null)
{
if ($alias === null) {
$alias = $this->alias;
}
self::getBounds(
$lat,
$long,
$distance,
// return values:
$lat_min,
$lat_max,
$long_min,
$long_max
);
return new CDbCriteria(
array(
'condition' => "{$this->lat_expr} BETWEEN :{$alias}_lat_min AND :{$alias}_lat_max"
. " AND {$this->long_expr} BETWEEN :{$alias}_long_min AND :{$alias}_long_max",
'params' => array(
"{$alias}_lat_min" => $lat_min,
"{$alias}_lat_max" => $lat_max,
"{$alias}_long_min" => $long_min,
"{$alias}_long_max" => $long_max,
)
)
);
}
/**
* Build criteria to select the computed radius from the given coordinates.
*
* Note that you will need to add a public property to your model, to hold the
* value that comes back from the database - the property name must match the
* alias used in this criteria, so that the framework can bind the value.
*
* Also note that {@see CDbCriteria::$select} defaults to "*", but that
* {@see CDbCriteria::mergeWith()} will discard the "*" select clause by default,
* which means that no colums will be selected, which is likely not what you want -
* to make sure that all of the columns from the root table are selected, add e.g.:
*
* $criteria->mergeWith(array('select' => 't.*'));
*
* Alternatively, the static {@see getDistance()} method can be used to compute the
* distance on demand, after executing the database query - the DBMS can generally
* provide higher accuracy (more decimals) than PHP, but you may or may not be
* comfortable introducing transient properties to persistent models.
*
* @see getDistance()
*
* @param float $lat
* @param float $long
* @param float $distance
* @param string|null $alias
*
* @return CDbCriteria
*/
public function getRadiusCriteria($lat, $long, $distance, $alias = null)
{
if ($alias === null) {
$alias = $this->alias;
}
$orig_lat = "{$alias}_lat";
$orig_long = "{$alias}_long";
$expr = self::getExpression(
$orig_lat,
$orig_long,
$this->lat_expr,
$this->long_expr
);
return new CDbCriteria(
array(
'select' => "{$expr} AS {$alias}",
'params' => array(
$orig_lat => $lat,
$orig_long => $long,
)
)
);
}
/**
* Build criteria matching records with coordinates falling within
* the bounds of a circle with the given minimum radius, at the
* given coordinates.
*
* @param float $lat
* @param float $long
* @param float $distance
* @param string|null $alias
*
* @return CDbCriteria
*/
public function getMaxRadiusCriteria($lat, $long, $distance, $alias = null)
{
if ($alias === null) {
$alias = $this->alias;
}
$orig_lat = "{$alias}_lat";
$orig_long = "{$alias}_long";
$distance_alias = "{$alias}_max";
$expr = self::getExpression(
$orig_lat,
$orig_long,
$this->lat_expr,
$this->long_expr
);
return new CDbCriteria(
array(
'condition' => "{$expr} <= :{$distance_alias}",
'params' => array(
$orig_lat => $lat,
$orig_long => $long,
$distance_alias => $distance,
)
)
);
}
}
@rcnankoe

Hi. Nice approach! But you should add km and miles as option on request as 'unit' or something.

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