Rails Postgis Nearest point - ruby-on-rails

Question

Try to calculate nearest points in some distance and one nearest point.
in db/migrate/xxx_create_points.rb":
class CreatePoints < ActiveRecord::Migration
def change
create_table :points do |t|
t.point :location, :geographic => true
t.string :name, :null => false
t.timestamps
end
change_table :points do |t|
t.index :location, :spatial => true
end
end
end
in config/routes.rb:
get 'points/:lat/:lon/:distance', to: 'points#index', :constraints => { :lat => /[^\/]+/, :lon => /[^\/]+/}
in controllers/points_controller.rb:
class PointsController < ApplicationController
def index
#points= Point.all
if params[:distance].present? && params[:lat].present? && params[:lon].present?
#distance = params[:distance].to_i
#latitude = params[:lat].to_f
#longitude = params[:lon].to_f
#points= Point.near(#latitude, #longitude, #distance)
#near = Point.nearest(#latitude, #longitude, 100).first
end
end
In models/point.rb:
class Point < ActiveRecord::Base
set_rgeo_factory_for_column(:location,
RGeo::Geographic.spherical_factory(:srid => 4326))
attr_accessible :location, :name
scope :near, lambda { |latitude, longitude, distance|
where("ST_Distance(location,
"+"'POINT(#{latitude} #{longitude})') < #{distance}")}
scope :nearest, lambda { |latitude, longitude, distance|
where("ST_Distance(location,
"+"'POINT(#{latitude} #{longitude})') < {distance}")
.order("ST_Distance(location, ST_GeographyFromText('POINT(#{latitude} #{longitude})'))").limit(1)}
end
In views/points/index.html.erb:
<script>
$.each(response.data, function(i, point) {
$('#map_canvas').gmap('addMarker', {
'position': new google.maps.LatLng(point.latitude, point.longitude), 'bounds': true });
}
$('#map_canvas').gmap('addShape', 'Circle', {
...
'center': new google.maps.LatLng(<%= "#{#latitude},#{#longitude}" %>),
'radius': 1 });
$('#map_canvas').gmap('addShape', 'Circle', {
...
'center': new google.maps.LatLng(<%= "#{#latitude},#{#longitude}" %>),
'radius': <%= #distance %> });
$('#map_canvas').gmap('addShape', 'Circle', {
...
'center': new google.maps.LatLng(<%= "#{#near.location.x},#{#near.location.y}" %>),
'radius': 2 });
</script>
Result in browser: http://xxx/points?distance=200&lat=55.7632500&lon=52.442000
What am I doing wrong?

Answer 1

PostGIS always uses the coordinate axis order (X Y) or (longitude latitude). I see snippets in your code that has this reversed:
ST_GeographyFromText('POINT(#{latitude} #{longitude})')
This needs to be switched:
ST_MakePoint(#{longitude}, #{latitude})::geography

Answer 2

Google maps uses mercator projections and the difference you see might be caused by the distance calculation differences between spherical projections you use in your model and mercator projections.
Try using RGeo's simple_mercator_factory in your Point class instead of using the spherical_factory.
RGeo's documentation gives you more details about that.
# Many popular visualization technologies, such as Google and Bing
# maps, actually use two coordinate systems. The first is the
# standard WSG84 lat-long system used by the GPS and represented
# by EPSG 4326. Most API calls and input-output in these mapping
# technologies utilize this coordinate system. The second is a
# Mercator projection based on a "sphericalization" of the WGS84
# lat-long system. This projection is the basis of the map's screen
# and tiling coordinates, and has been assigned EPSG 3857.