Question

Given the code below, how do I compare a List of objects’s values with a test value?

I’m building a geolocation application. I’ll be passing in longitude and latitude and would like to have the service answer back with the location closest to those values.

I started down the path of converting to a string, and formatting the values down to two decimal places, but that seemed a bit too ghetto, and I’m looking for a more elegant solution.

public class Location : IEnumerable
{
    public string label { get; set; }
    public double lat { get; set; }
    public double lon { get; set; }

    //Implement IEnumerable
    public IEnumerator GetEnumerator()
    {
        return (IEnumerator)this;
    }

}
[HandleError]
public class HomeController : Controller
{
    private List<Location> myList = new List<Location>
 {             
    new Location {
        label="Atlanta Midtown", 
        lon=33.657674, 
        lat=-84.423130},
    new Location {
        label="Atlanta Airport", 
        lon=33.794151, 
        lat=-84.387228},
    new Location {
        label="Stamford, CT", 
        lon=41.053758, 
        lat=-73.530979}, ...
}

 public static int Main(String[] args)
 {
     string inLat = "-80.987654";
     double dblInLat = double.Parse(inLat);

     // here's where I would like to find the closest location to the inLat
     // once I figure out this, I'll implement the Longitude, and I'll be set
 }

Answer 1

I found this which someone created that calculates distances between two distances across the globe using one of several different methods. I had to convert the .NET project to the updated VS2008, but that seemed to work fine. Then I just added this project to my solution and made a reference to it.

My code then became:

string inLat = "-80.987654";
string inLon = "33.521478";
var miles = GetNearestLocation(inLat, inLon);

public double GetNearestLocation(string lat, string lon)
{
    double dblInLat = double.Parse(lat);
    double dblInLon = double.Parse(lon);

    // instantiate the calculator
    GeodeticCalculator geoCalc = new GeodeticCalculator();

    // select a reference elllipsoid
    Ellipsoid reference = Ellipsoid.WGS84;

    // set user's current coordinates
    GlobalCoordinates userLocation;
    userLocation = new GlobalCoordinates(
        new Angle(dblInLon), new Angle(dblInLat)
    );

    // set example coordinates- when fully fleshed out, 
    //    this would be passed into this method
    GlobalCoordinates testLocation;
    testLocation= new GlobalCoordinates(
        new Angle(41.88253), new Angle(-87.624207) // lon, then lat
    );

    // calculate the geodetic curve
    GeodeticCurve geoCurve = geoCalc.CalculateGeodeticCurve(reference, userLocation, testLocation);
    double ellipseKilometers = geoCurve.EllipsoidalDistance / 1000.0;
    double ellipseMiles = ellipseKilometers * 0.621371192;
    /*
    Console.WriteLine("2-D path from input location to test location using WGS84");
    Console.WriteLine("   Ellipsoidal Distance: {0:0.00} kilometers ({1:0.00} miles)", ellipseKilometers, ellipseMiles);
    Console.WriteLine("   Azimuth:              {0:0.00} degrees", geoCurve.Azimuth.Degrees);
    Console.WriteLine("   Reverse Azimuth:      {0:0.00} degrees", geoCurve.ReverseAzimuth.Degrees);
    */
    return ellipseMiles;
}