how geo_distance query works under the hood in Elasticsearch?

maulik_trapasiya · June 4, 2023, 9:26am

I need to use geo_distance query on Elasticsearch. Need info about how it works under the hood and what is latency? I am not able to find any doc relevant to this. please help

stephenb · June 4, 2023, 8:38pm

Hi @maulik_trapasiya Welcome to the community....

First with respect to latency, we can not tell you that as there are many factors... the size of your data set, the filters, the number of results within the distance, the HW profile etc.. etc... I would encourage you to do your own testing.

And you can look at the benchmarks here

https://elasticsearch-benchmarks.elastic.co/

I am not the Geo Expert but here is the code and it shows the simple calculations... there are planar and arc calculations.

github.com

elastic/elasticsearch/blob/6179ae84f0cda5e2cb9e8070bcd88ce5ae699b9d/server/src/main/java/org/elasticsearch/common/geo/GeoUtils.java#L503


      
           * is outside the range.
           */
          public static int checkPrecisionRange(int precision) {
              if ((precision < 1) || (precision > 12)) {
                  throw new IllegalArgumentException("Invalid geohash aggregation precision of " + precision + ". Must be between 1 and 12.");
              }
              return precision;
          }
          
          
/** Return the distance (in meters) between 2 lat,lon geo points using the haversine method implemented by lucene */
          public static double arcDistance(double lat1, double lon1, double lat2, double lon2) {
              return SloppyMath.haversinMeters(lat1, lon1, lat2, lon2);
          }
          
          
/**
           * Return the distance (in meters) between 2 lat,lon geo points using a simple tangential plane
           * this provides a faster alternative to {@link GeoUtils#arcDistance} but is inaccurate for distances greater than
           * 4 decimal degrees
           */
          public static double planeDistance(double lat1, double lon1, double lat2, double lon2) {
              double x = Math.toRadians(lon2 - lon1) * Math.cos(Math.toRadians((lat2 + lat1) / 2.0));

and further here, I think the formulae are here

github.com

elastic/elasticsearch/blob/6179ae84f0cda5e2cb9e8070bcd88ce5ae699b9d/libs/geo/src/main/java/org/elasticsearch/geometry/simplify/SloppyMath.java#L31


      
           *
           * <p>Error is at most 4E-1 (40cm) from the actual haversine distance, but is typically much
           * smaller for reasonable distances: around 1E-5 (0.01mm) for distances less than 1000km.
           *
           * @param lat1 Latitude of the first point.
           * @param lon1 Longitude of the first point.
           * @param lat2 Latitude of the second point.
           * @param lon2 Longitude of the second point.
           * @return distance in meters.
           */
          public static double haversinMeters(double lat1, double lon1, double lat2, double lon2) {
              return haversinMeters(haversinSortKey(lat1, lon1, lat2, lon2));
          }
          
          
/**
           * Returns the Haversine distance in meters between two points given the previous result from
           * {@link #haversinSortKey(double, double, double, double)}
           *
           * @return distance in meters.
           */
          public static double haversinMeters(double sortKey) {

It looks like it follows the Haversine for the Arc distance method and the distance using a simple tangential plane for the planar distance, Whether this is precise enough for your use case is up to you perhaps you can provide further information if needed and we can take a deeper look.

system · July 2, 2023, 8:38pm

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how geo_distance query works under the hood in Elasticsearch?

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