Adapting Sunspot pre-2.0 spatial search on Solr 1.4 for Solr 3 spatial search api

1-schema-tweaks.xml

<schema>
  <types>
    <!-- add a location fieldtype, which splits a string into component subfields -->
    <fieldType name="location" class="solr.LatLonType" subFieldSuffix="_coordinate"/>
  </types>
  <fields>
    <!-- add the location field, and the coordinate subtype -->
    <field name="location" type="location" indexed="true" />
    <dynamicField name="*_coordinate"  type="tdouble" indexed="true"  stored="false"/>
  </fields>
</schema>

2-sunspot-tweaks.rb

# index the location as a "lat,lng" string
searchable do
  string(:location, :as => :location) { [lat,lng].join(",") }
end


# change your searches from this...
search do
  with(:lat_lng).near(lat, lng, :precision => foo)
end

# ...to this
search do
  adjust_solr_params do |p|
    p['fq'] = "{!geofilt sfield=location pt=#{lat,lng} d=#{params[:distance]}}"
  end
end

# ...or this
search do
  adjust_solr_params do |p|
    p['fq']     = '{!geofilt}'
    p['sfield'] = 'location'
    p['pt']     = [lat,lng].join(',')
    p['d']      = params[:distance] # kilometers
  end
end

disclaimer: these are untested notes written off the top of my head. useful as a place to start your own research, but your mileage may vary. feedback welcome ;-)