C# - LINQ - shortest distance by GPS latitude and longitude
c# entity-framework gps linq linq-to-entities
Question
I have database and in it I have class hotel with gps coordinates. I want to get closest places to coordinates which I choose.
I think It should look like this (I found many example codes here and like this one):
var coord = new GeoCoordinate(latitude, longitude);
var nearest = (from h in db.hotels
let geo = new GeoCoordinate(h.gps.lat, h.gps.lng)
orderby geo.GetDistanceTo(coord)
select h).Take(10);
The problem is that I have this error when I tried to search for something:
Only parameterless constructors and initializers are supported in LINQ to Entities
I tried to google it and I found that dividing that linq into two can help me but I am not sure how. Thanks for help.
Accepted Answer
You can use the object initializer instead of parameterized constructor:
var nearest = (from h in db.hotels
let geo = new GeoCoordinate{ Latitude = h.gps.lat, Longitude = h.gps.lng}
orderby geo.GetDistanceTo(coord)
select h).Take(10);
But you will likely have problems caused by the GetDistanceTo method, could you provide the implementation of that method?
Popular Answer
I have had a reasonable about of success using this implementation of the Haversine Distance formula
var startPoint = new { Latitude = 1.123, Longitude = 12.3 };
var closest = entities.Something.OrderBy(x => 12742 * SqlFunctions.Asin(SqlFunctions.SquareRoot(SqlFunctions.Sin(((SqlFunctions.Pi() / 180) * (x.Latitude - startPoint.Latitude)) / 2) * SqlFunctions.Sin(((SqlFunctions.Pi() / 180) * (x.Latitude - startPoint.Latitude)) / 2) +
SqlFunctions.Cos((SqlFunctions.Pi() / 180) * startPoint.Latitude) * SqlFunctions.Cos((SqlFunctions.Pi() / 180) * (x.Latitude)) *
SqlFunctions.Sin(((SqlFunctions.Pi() / 180) * (x.Longitude - startPoint.Longitude)) / 2) * SqlFunctions.Sin(((SqlFunctions.Pi() / 180) * (x.Longitude - startPoint.Longitude)) / 2)))).Take(5);
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