From d7e40fb1d720b459ddc1055c3a1e496c092944c7 Mon Sep 17 00:00:00 2001
From: Alex Reisner <alex@alexreisner.com>
Date: Sat, 26 Mar 2011 18:58:03 -0400
Subject: [PATCH] Improve SQLite distance calculation.
Multiply by .707 (sin(45)) instead of .5.
---
lib/geocoder/orms/active_record.rb | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/lib/geocoder/orms/active_record.rb b/lib/geocoder/orms/active_record.rb
index 44098b8f..b4079dae 100644
--- a/lib/geocoder/orms/active_record.rb
+++ b/lib/geocoder/orms/active_record.rb
@@ -157,8 +157,11 @@ module Geocoder::Orm
dx = Geocoder::Calculations.longitude_degree_distance(30, options[:units] || :mi)
dy = Geocoder::Calculations.latitude_degree_distance(options[:units] || :mi)
- distance = "(#{dy} * ABS(#{lat_attr} - #{latitude}) / 2) + " +
- "(#{dx} * ABS(#{lon_attr} - #{longitude}) / 2)"
+ # sin of 45 degrees = average x or y component of vector
+ factor = Math.sin(Math::PI / 4)
+
+ distance = "(#{dy} * ABS(#{lat_attr} - #{latitude}) * #{factor}) + " +
+ "(#{dx} * ABS(#{lon_attr} - #{longitude}) * #{factor})"
default_near_scope_options(latitude, longitude, radius, options).merge(
:select => "#{options[:select] || '*'}, " +
"#{distance} AS distance" +
--
GitLab