[jira] [Commented] (SIS-45) Performance improvement of queryByPointRadius

["Peter Karich (Commented) (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SIS-45?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13257764#comment-13257764 ] 

Peter Karich commented on SIS-45:
---------------------------------

Normalizing the distance leeds to some more (20%) improvements:

{code}
   double normedRadius =  DistanceUtils.getNormalizedDist(radiusKM);
   ...  queryByPointRadius(point, normedRadius, ..
{code}

{code}
   if (DistanceUtils.getNormedHaversineDistance(data[i].getLatLon().getLat(), data[i]
              .getLatLon().getLon(), point.getLat(), point.getLon()) <= normedRadius) {
            matches.add(data[i]);
          }
{code}

with:

{code}
  public static double getNormedHaversineDistance(double fromLat, double fromLon, double toLat, double toLon) {
    double dLat = Math.toRadians(toLat - fromLat);
        double dLon = Math.toRadians(toLon - fromLon);
        return Math.sin(dLat / 2) * Math.sin(dLat / 2)
                + Math.cos(Math.toRadians(fromLat)) * Math.cos(Math.toRadians(toLat)) * Math.sin(dLon / 2) * Math.sin(dLon / 2);
  }

  public static double getNormalizedDist(double radiusKM) {
    double tmp = Math.sin(radiusKM / 2 / EARTH_RADIUS);
    return tmp * tmp;
  }
{code}

but I still feel bad (programming in the dark without unit tests ...)
                
> Performance improvement of queryByPointRadius
> ---------------------------------------------
>
>                 Key: SIS-45
>                 URL: https://issues.apache.org/jira/browse/SIS-45
>             Project: Spatial Information Systems
>          Issue Type: Improvement
>            Reporter: Peter Karich
>
> If I didn't make a mistake a search with the normal distance method took ~2.4s and with this distance method it takes only about 0.7s:
> {code}
>   public static double getHaversineDistance(double fromLat, double fromLon, double toLat, double toLon) {
>     double dLat = Math.toRadians(toLat - fromLat);
>         double dLon = Math.toRadians(toLon - fromLon);
>         double a = Math.sin(dLat / 2) * Math.sin(dLat / 2)
>                 + Math.cos(Math.toRadians(fromLat)) * Math.cos(Math.toRadians(toLat)) * Math.sin(dLon / 2) * Math.sin(dLon / 2);
>         return EARTH_RADIUS * 2 * Math.asin(Math.sqrt(a));
>   }
> {code}
> Also one should think about normalizing the distance before the search so that one does not need the whole last line which should give further speed improvements.
> I'm still unsure why it takes roughly the same time in my example for 10km, 20km and 40kmm where at every step a lot more nodes are involved. Normally I would say the mode nodes - the more comparisons it'll take and the slower it should get. But it doesn't. Probably I'm measuring wrong?

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