RE: [OpenMap Users] sort lat,lon pairs (or find distance)

From: David Ward <mry_yachtsman_at_hotmail.com>
Date: Wed, 11 Aug 2004 23:32:51 -0700

Ben,

Try the code below. Should do the job for you.

Cheers,
David

    /**
     * Sort a List of LatLonPoints by their distance from a reference point.
     * The contents of <CODE>latlonlist</CODE> will be sorted in place.
     * _at_param latlonlist list of LatLonPoints to sort. This list will be
modified.
     * _at_param llp reference LatLonPoint.
     * _at_return the sorted list.
     */
    public List sortLatLons(List latlonlist, LatLonPoint llp){
        Collections.sort(latlonlist, new DistanceComparator(llp));
        return latlonlist;
    }

     /**
     * Compares to LatLonPoints by their distance from a reference
LatLonPoint.
     */
    public class DistanceComparator implements Comparator {
        LatLonPoint refPt;

        /**
         * Constructor for a DistanceComparator of LatLonPoints to a
reference point.
         * _at_param llp reference LatLonPoint against which to compare.
         */
        public DistanceComparator(LatLonPoint llp) {
            refPt = llp;
        }

        /**
         * Compares its two arguments for order. Returns a negative integer,
zero, or a
         * positive integer if the first argument is less than, equal to, or
greater than
         * the second.
         * _at_param o1 first object to be compared.
         * _at_param o2 first object to be compared.
         * _at_return a negative integer, zero, or a positive integer as the
first argument is less than, equal to, or greater than the second.
         */
        public int compare(Object o1, Object o2) {
            //Assume the objects are always LatLonPoints
            LatLonPoint llp1 = (LatLonPoint)o1;
            LatLonPoint llp2 = (LatLonPoint)o2;

            //Get the distances from the reference point
            float dist1 = GreatCircle.spherical_distance(refPt.radlat_,
refPt.radlon_,
            llp1.radlat_, llp1.radlon_);
            float dist2 = GreatCircle.spherical_distance(refPt.radlat_,
refPt.radlon_,
            llp2.radlat_, llp2.radlon_);
            // calculate the difference
            double diff = dist1-dist2;

            //make sure we return an appropriate result,
            //can not simply cast the difference to int
            if (diff == 0.0f) return 0;
            return diff < 0 ? -1 : 1;

        }

    }



>-----Original Message-----
>From: owner-openmap-users_at_bbn.com [mailto:owner-openmap-users_at_bbn.com]On
>Behalf Of Ben Podoll
>Sent: Wednesday, August 11, 2004 6:46 PM
>To: openmap-users_at_bbn.com
>Subject: [OpenMap Users] sort lat,lon pairs (or find distance)
>
>
>I have a list of LatLonPoint objects, and I want to sort them by distance
>from a LatLonPoint. Hence I want to make a method that could do this:
>
>public List sortLatLons(List latlonlist, LatLonPoint llp){
> //where the latlonlist is a List of LatLonPoint objects
> //sort the latlonlist in order closest to the llp
> //return the list
>}
>
>What can I use in OpenMap to accomplish this goal?
>
>Thanks,
>Ben
>
>
>--
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Cheers,
David

-----------------
David J. Ward
mry_yachtsman_at_hotmail.com

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Received on Thu Aug 12 2004 - 02:34:56 EDT