how to cluster points of interest by lat lon for my WP7 app

Question

I have alread asked this question on SO, so I appologies if duplicating this is bad form. I will link to each of the sites if I get the right answer...

http://stackoverflow.com/questions/5479589/how-to-group-points-of-interest-by-lat-lon-for-my-wp7-app

I have a collection of my own PointOfInterest classes (approx. 1500) each having their own Latitude and Longitude double properties.

Im trying to draw them on my screen, but at a certain logical zoom level, there is no point showing some of them because they are so close together.

How can I very efficiently group POI's by their lat lon properties?

I have this type of thing:

var pointOfInterests = (from p in PointsOfInterest select p).Distinct(new EqualityComparer()).ToList();

where the EqualityComparer is:

public class EqualityComparer : IEqualityComparer<PointOfInterest>
{
    public bool Equals(PointOfInterest x, PointOfInterest y)
    {
        return Math.Round(x.Latitude.Value, PointOfInterest.DecimalPlaceFilterLevel) == Math.Round(y.Latitude.Value, PointOfInterest.DecimalPlaceFilterLevel) &&
            Math.Round(x.Longitude.Value, PointOfInterest.DecimalPlaceFilterLevel) == Math.Round(y.Longitude.Value, PointOfInterest.DecimalPlaceFilterLevel);
    }

    public int GetHashCode(PointOfInterest obj)
    {
        return Math.Round(obj.Latitude.Value, PointOfInterest.DecimalPlaceFilterLevel).GetHashCode() ^ Math.Round(obj.Longitude.Value, PointOfInterest.DecimalPlaceFilterLevel).GetHashCode();
    }
}

and the PointOfInterest.DecimalPlaceFilterLevel is a static int property that I set when the user is at a certian zoom level.

But this isnt working, I keep getting overlapping POI's and its not very fast... since I am on the phone, I need it to perform very well.

Thanks for any help you can give

Answer 1

The ArcGIS WP7 api has clustering capabilities.

Answer 2

I am working on a similar problem with iOS. I have come across this answer How do I cluster XY point data? (ArcGIS 9.3) which I am trying to incorporate into the iOS app. I've not yet figured out how best to apply it (server or client), but the theory seems sound. Essentially, create a grid and then map each point to the closest corner. I'll follow this post and update with anything I find as I work through this one...