我们希望在ASP.NET 2012中使用LINQ从数据库接收附近地点的列表,并希望对我们的策略提供一些反馈。
我的表格和假数据:
PlaceId Name Latitude Longitude
1 A 18.1 20.1
2 B 18.2 20.2
3 C 18.3 20.3
1)在我们的项目中,客户当前位置(纬度和经度)被视为输入
2)在服务器端,根据客户端的当前位置,我们需要使用LINQ从数据库中查找附近的位置
这是我之前使用的SQL代码,但现在我们想使用LINQ。
SELECT name, Latitude, Longitude ,
( 3959 * acos( cos( radians(?) )* cos( radians( Latitude) ) * cos( radians( Longitude ) - radians(?) )
+ sin( radians(?) ) * sin( radians( Latitude) ) ) ) AS distance
FROM TABLE_NAME
HAVING distance < ?
ORDER BY distance LIMIT 0 , 20
[但问题是如何在LINQ中编写这样的查询。]
我的工作:
在搜索解决方案时,我遇到了这段代码
var Value1 = 57.2957795130823D;
var Value2 = 3958.75586574D;
var searchWithin = 20;
double latitude = ConversionHelper.SafeConvertToDoubleCultureInd(Latitude, 0),
longitude = ConversionHelper.SafeConvertToDoubleCultureInd(Longitude, 0);
var location = (from l in sdbml.Places
let temp = Math.Sin(Convert.ToDouble(l.Latitude) / Value1) * Math.Sin(Convert.ToDouble(latitude) / Value1) +
Math.Cos(Convert.ToDouble(l.Latitude) / Value1) *
Math.Cos(Convert.ToDouble(latitude) / Value1) *
Math.Cos((Convert.ToDouble(longitude) / Value1) - (Convert.ToDouble(l.Longitude) / Value1))
let calMiles = (Value2 * Math.Acos(temp > 1 ? 1 : (temp < -1 ? -1 : temp)))
where (l.Latitude > 0 && l.Longitude > 0)
orderby calMiles
select new location
{
Name = l.name
});
return location .ToList();
但问题是,如何引用ConversionHelper或它来自哪个命名空间。
感谢所有建议。
答案 0 :(得分:4)
所以,如果你想要的只是计算两个坐标之间的距离,为什么不使用Dot Net的GeoCoordinate
?
它类似于
var firstCordinate = new GeoCoordinate(latitude1, longitude1);
var secondCordinate = new GeoCoordinate(latitude2, longitude2);
double distance = firstCordinate.GetDistanceTo(secondCordinate);
你可以在命名空间System.Device.Location
中找到它。
因此,这将使您免除所有Math.Cos
和Math.Sin
,并且您的linq将简单明了。 (可能是foreach循环会这样做)
因此您的整个查询可归纳为:
List<Location> locations = new List<Location>();
foreach(var place in sdbml.Places)
{
//your logic to compare various place's co-ordinates with that of
//user's current co-ordinate
}
答案 1 :(得分:3)
以下是我最终需要解决的代码
1)创建一个类,比如
DistanceModel.cs
public class DistanceModel
{
public int PlaceId { get; set; }
public string Name { get; set; }
public double Latitute { get; set; }
public double Longitude { get; set; }
}
2)然后在您想要的任何文件中包含以下代码,例如
MainPage.cs
/*Call GetAllNearestFamousPlaces() method to get list of nearby places depending
upon user current location.
Note: GetAllNearestFamousPlaces() method takes 2 parameters as input
that is GetAllNearestFamousPlaces(user_current_Latitude,user_current_Longitude) */
public void GetAllNearestFamousPlaces(double currentLatitude,double currentLongitude)
{
List<DistanceModel> Caldistance = new List<DistanceModel>();
var query = (from c in sdbml.Places
select c).ToList();
foreach (var place in query)
{
double distance = Distance(currentLatitude, currentLongitude, place.Latitude, place.Logitude);
if (distance < 25) //nearbyplaces which are within 25 kms
{
DistanceModel dist = new DistanceModel();
dist.Name = place.PlaceName;
dist.Latitute = place.Latitude;
dist.Longitude = place.Logitude;
dist.PlaceId = place.PlaceId;
Caldistance.Add(getDiff);
}
}
}
private double Distance(double lat1, double lon1, double lat2, double lon2)
{
double theta = lon1 - lon2;
double dist = Math.Sin(deg2rad(lat1)) * Math.Sin(deg2rad(lat2)) + Math.Cos(deg2rad(lat1)) * Math.Cos(deg2rad(lat2)) * Math.Cos(deg2rad(theta));
dist = Math.Acos(dist);
dist = rad2deg(dist);
dist = (dist * 60 * 1.1515) / 0.6213711922; //miles to kms
return (dist);
}
private double deg2rad(double deg)
{
return (deg * Math.PI / 180.0);
}
private double rad2deg(double rad)
{
return (rad * 180.0 / Math.PI);
}
它对我有用,希望它会帮助你。