Ashfaq Ahmed - 1 year ago 199

C# Question

I am working on a application where I need to get nearby location,

my web service will receive 2 parameters (decimal longitude, decimal latitude )

I have a table where the locations are saved in database with longitude and latitude fields,

I want to retrieve the nearest locations.

Can anyone help?

Here is my code:

`var locations = from l in locations`

select l

Here are further details about this :

i have a 2 fields (decimal(18, 2) null) 1 latitude, 2 longitude inside a database table,

and i have a method

`public List<Locations> GetLocation(decimal? Long, decimal? lat)`

{

var Loc = from l in Locations

//// now here is how to get nearest location ? how to query?

//// i have also tried Math.Abs(l.Lat - lat) its giving error about nullable decimal always hence i have seted decimal to nullable or converted to nullable

//// also i have tried where (l.lat - Lat) * (l.lon - Long) this is also giving error about can not convert decimal to bool

return Loc.ToList();

}

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Answer Source

Here is Solution

```
var constValue = 57.2957795130823D
var constValue2 = 3958.75586574D;
var searchWithin = 20;
double latitude = ConversionHelper.SafeConvertToDoubleCultureInd(Latitude, 0),
longitude = ConversionHelper.SafeConvertToDoubleCultureInd(Longitude, 0);
var loc = (from l in DB.locations
let temp = Math.Sin(Convert.ToDouble(l.Latitude) / constValue) * Math.Sin(Convert.ToDouble(latitude) / constValue) +
Math.Cos(Convert.ToDouble(l.Latitude) / constValue) *
Math.Cos(Convert.ToDouble(latitude) / constValue) *
Math.Cos((Convert.ToDouble(longitude) / constValue) - (Convert.ToDouble(l.Longitude) / constValue))
let calMiles = (constValue2 * 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 loc .ToList();
```

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