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    <p>Write a method in your BI that gives you all the restaurants between the bounds of the Map (or within a given distance from the center (LatLon) of the Map. I used to do it embedding a custom function in Sqlite </p> <pre><code>[SqliteFunctionAttribute(Name = "distance", Arguments = 4, FuncType = FunctionType.Scalar)] class SqliteDistance : SqliteFunction { public override object Invoke(object[] args) { double latA = System.Convert.ToDouble(args[0]); double lonA = System.Convert.ToDouble(args[1]); double latB = System.Convert.ToDouble(args[2]); double lonB = System.Convert.ToDouble(args[3]); const double R = 6371; const double pigreco = 3.1415927; double lat_alfa, lat_beta; double lon_alfa, lon_beta; double fi; double p, d; /* Converte i gradi in radianti */ lat_alfa = pigreco * latA / 180; lat_beta = pigreco * latB / 180; lon_alfa = pigreco * lonA / 180; lon_beta = pigreco * lonB / 180; /* Calcola l'angolo compreso fi */ fi = Math.Abs(lon_alfa - lon_beta); /* Calcola il terzo lato del triangolo sferico */ p = Math.Acos(Math.Sin(lat_beta) * Math.Sin(lat_alfa) + Math.Cos(lat_beta) * Math.Cos(lat_alfa) * Math.Cos(fi)); /* Calcola la distanza sulla superficie terrestre R = ~6371 km */ d = p * R; return (d); } } </code></pre> <p>then in your query :</p> <pre><code>Public List&lt;Restaurant&gt; GiveMeRestaurants(double fromLat, double fromLon) { String sql="Select * from restaurants where distance('" + fromLat.ToString() + "','" + fromLon.ToString() + "',restaurants.Latitude,restaurants.Longitude) &lt;= 100 )"; } </code></pre> <p>This can give you also the straight line distance.</p> <ol> <li>For road distance maybe you can call google play services using the center map and the coordinates or the restaurant</li> </ol>
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    1. COThanks Luca for this. First, can you please change the comments in your code to English so that I can understand it a bit more? :) Secondly, if I write this in my BI, I will have to call it 500 times, i.e. for every restaurant, and then see whether it lies within my radius or not, correct?
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      1. USAhmed Salman Tahir
    2. CODon't mind the comments, they simply explain the steps for calculate geodetic distance between two points on the hearth :) No, you haven't to call it 500 times. Is a single query that returns all the restaurants in a range (of 100 km in this case) from the center point you set(the ceneter of the map showed). When the user pan the map, the center will change, and you'll have to re-execute the query and show the new restaurants on the map. :)
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    3. COBut as this method is in BI instead of database, won't I always have to fetch all 500 restaurants from database and then filter them on BI (i.e. actually calling this method for all of them) and then the web service handing over the filtered list to the app?
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