我的事件数据库有多个事件,每个事件都有不同的纬度和经度,如果我当前的纬度是30.7263962,经度是76.7664144,我如何从数据库中获取距离我位置不到100公里范围的事件?谁能建议我查询?感谢
答案 0 :(得分:0)
您可以弯曲的一些示例代码(我已经尝试适应您的需求,但已做出一些猜测)。
这是使用Rhumb线(或loxodrome)
<?php
function search($device_latitude, $device_longitude, $radius, $radius_type)
{
$events = array();
$sql = "SELECT `event_id`, `last_updated`, `location_lat`, `location_long` FROM `event`";
$query = $this->db->query($sql);
if ($query->num_rows() > 0)
{
foreach ($query->result() as $row)
{
$geo_data = $this->_bearing_distance_calc($device_latitude, $device_longitude, $row->location_lat, $row->location_long, $radius_type);
$geo_data['radius_type'] = $radius_type;
// $geo_data contains => 'distance', 'bearing'
if($geo_data['distance'] <= $radius)
{
$events[] = $this->event->load($row->event_id);
}
}
return $events;
}
$this->error_msg = "Search failed.";
return NULL;
}
function _bearing_distance_calc($device_latitude, $device_longitude, $event_latitude, $event_longitude, $radius_type)
{
// using Rhumb lines(or loxodrome)
// convert to rads for php trig functions
$device_latitude = deg2rad($device_latitude);
$device_longitude = deg2rad($device_longitude);
$event_latitude = deg2rad($event_latitude);
$event_longitude = deg2rad($event_longitude);
// calculate delta of lat and long
$delta_latitude = $event_latitude-$device_latitude;
$delta_longitude = $event_longitude-$device_longitude;
// earth radius
if ($radius_type == 'Miles')
{
$earth_radius = 3959;
}
else
{
$earth_radius = 6371;
}
// now lets start mathing !!
$dPhi = log(tan($event_latitude/2+M_PI/4)/tan($device_latitude/2+M_PI/4));
if ($dPhi != 0)
{
$q = $delta_latitude/$dPhi;
}
else
{
$q = cos($device_latitude);
}
//$q = (!is_nan($delta_latitude/$dPhi)) ? $delta_latitude/$dPhi : cos($device_latitude); // E-W line gives dPhi=0
// if dLon over 180° take shorter rhumb across 180° meridian:
if (abs($delta_longitude) > M_PI)
{
$delta_longitude = $delta_longitude>0 ? -(2*M_PI-$delta_longitude) : (2*M_PI+$delta_longitude);
}
$geo_data = array();
$geo_data['distance'] = sqrt($delta_latitude*$delta_latitude + $q*$q*$delta_longitude*$delta_longitude) * $earth_radius;
$bearing = rad2deg(atan2($delta_longitude, $dPhi));
if($bearing < 0)
{
$bearing = 360 + $bearing;
}
$geo_data['bearing'] = $bearing;
return $geo_data;
}
答案 1 :(得分:0)
您需要的是将距离转换为经度和纬度,根据大致在边界框中的条目进行过滤,然后进行更精确的距离过滤。这是一篇很好的论文,解释了如何做到这一切:
http://www.scribd.com/doc/2569355/Geo-Distance-Search-with-MySQL