Question

I want to be able to display a Bing map in a Windows 8/Store app with an array of pushpins/waypoints at a zoom setting that will show every location, but no more than that – IOW, I want as much detail as possible while still showing all of the locations/coordinates.

I have this pseudocode:

public static int GetMapZoomSettingForCoordinates(List<String> coordinatesList)
{
    string furthestNorth = GetFurthestNorth(coordinatesList);
    string furthestSouth = GetFurthestSouth(coordinatesList);
    string furthestEast = GetFurthestEast(coordinatesList);
    string furthestWest = GetFurthestWest(coordinatesList);
    int milesBetweenNorthAndSouthExtremes = GetMilesBetween(furthestNorth, furthestSouth);
    int milesBetweenEastAndWestExtremes = GetMilesBetween(furthestEast, furthestWest);
    int greaterCardinalDistance = Math.Max(milesBetweenNorthAndSouthExtremes, milesBetweenEastAndWestExtremes);
    return GetZoomSettingForDistance(greaterCardinalDistance);
}

…but the “sticking point” (the hard part) are the “milesBetween” functions. Is there an existing algorithm for computing the miles between two coordinates?

I do realize this is a U.S.-centric bunch of code for now (miles vs. kilometers); that is, for now, as designed.

UPDATE

This is my new pseudocode (actual compiling code, but untested):

public static int GetMapZoomSettingForCoordinates(List<string> coordinatePairsList)
{
    List<double> LatsList = new List<double>();
    List<double> LongsList = new List<double>();
    List<string> tempList = new List<string>();

    foreach (string s in coordinatePairsList)
    {
        tempList.AddRange(s.Split(';'));
        double dLat;
        double.TryParse(tempList[0], out dLat);
        double dLong;
        double.TryParse(tempList[0], out dLong);
        LatsList.Add(dLat);
        LongsList.Add(dLong);
        tempList.Clear();
    }

    double furthestNorth = GetFurthestNorth(LatsList);
    double furthestSouth = GetFurthestSouth(LatsList);
    double furthestEast = GetFurthestEast(LongsList);
    double furthestWest = GetFurthestWest(LongsList);
    int milesToDisplay = 
        HaversineInMiles(furthestWest, furthestNorth, furthestEast, furthestSouth);
    return GetZoomSettingForDistance(milesToDisplay);
}

private static double GetFurthestNorth(List<double> longitudesList)
{
    double northernmostVal = 0.0;
    foreach (double d in longitudesList)
    {
        if (d > northernmostVal)
        {
            northernmostVal = d;
        }
    }
    return northernmostVal;
}

…I still don’t know what GetZoomSettingForDistance() should be/do, though…

UPDATE 2

This is “more better”:

public static int GetMapZoomSettingForCoordinates(List<Tuple<double, double>> coordinatePairsList)
{
    var LatsList = new List<double>();
    var LongsList = new List<double>();

    foreach (Tuple<double,double> tupDub in coordinatePairsList)
    {
        LatsList.Add(tupDub.Item1);
        LongsList.Add(tupDub.Item2);
    }

    double furthestNorth = GetFurthestNorth(LongsList);
    double furthestSouth = GetFurthestSouth(LongsList);
    double furthestEast = GetFurthestEast(LatsList);
    double furthestWest = GetFurthestWest(LatsList);
    int milesToDisplay =
        HaversineInMiles(furthestWest, furthestNorth, furthestEast, furthestSouth); 
    return GetZoomSettingForDistance(milesToDisplay);
}

UPDATE 3

I realized that my logic was backwards, or wrong, at any rate, regarding meridians of longitude and parallels of latitude. While it’s true that meridians of longitude are the vertical lines (“drawn” North-to-South or vice versa) and that parallels of latitude are the horizontal lines (“drawn” East-to-West), points along those line represent the North-South location based on parallels of latitude, and represent East-West locations based on meridians of longitude. This seemed backwards in my mind until I visualized the lines spinning across (longitude) and up and over (latitude) the earth, rather than simply circling the earth like the rings of Saturn do; what also helped get my perception right was reminding myself that it is the values of the meridians of longitude that determine in which time zone one finds themselves. SO, the code above should change to pass latitudes to determine furthest North and furthest South, and conversely pass longitudes to determine furthest East and furthest West.

Answer 1

You can use the Haversine formula to compute the distance along the surface of a sphere.

Here’s a C++ function to compute the distance using the Earth as the size of the sphere. It would easily be convertible to C#.

Note that the formula can be simplified if you want to just find the distance either latitudinally or longitudinally (which it sounds like you are trying to do).