PostGIS笔记（上） PostGIS笔记（中） 上篇说了为什么用Geography，这篇具体讲怎么取“范围n米以内的数据”。 Rails里运行Migration，建Portal Model，以下是Schema t.geography “lonlat”, limit: {:srid=>4326, :type=>”point”, :geography=>true}, null: false t.datetime “created_at”, null: false t.datetime “updated_at”, null: false t.index [“lonlat”], name: “index_parks_on_lonlat”, using: :gist 距离东京站1km内所有的portals ST_Distance float ST_Distance(geography gg1, geography gg2, boolean use_spheroid); SELECT id, name FROM portals WHERE ST_Distance(lonlat, ST_GeogFromText(‘POINT(139.767052 35.681167)’)) < 1000; ST_DWithin boolean ST_DWithin(geography gg1, geography gg2, double precision…