Module: Wukong::Geolocated::ByCoordinates

Extended by:
Gorillib::Concern
Defined in:
lib/wu/geo/geolocated.rb

Overview

field :longitude, type: Float, description: “Longitude (X) of a point, in decimal degrees” field :latitude, type: Float, description: “Latitude (Y) of a point, in decimal degrees” field :zoom_level, type: Integer, description: “Zoom level of tile to fetch. An integer between 0 (world) and 16 or so” field :quadkey, type: String, description: “Quadkey of tile, eg 002313012” field :tile_x, type: Integer, description: “Tile X index, an integer between 0 and 2^zoom_level - 1” field :tile_y, type: Integer, description: “Tile Y index, an integer between 0 and 2^zoom_level - 1”

Instance Method Summary collapse

Instance Method Details

#bbox_for_radius(radius) ⇒ Object 



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# File 'lib/wu/geo/geolocated.rb', line 93

def bbox_for_radius(radius) ; Wukong::Geolocated.lng_lat_rad_to_bbox(longitude, latitude, radius) ; end

#lng_lat ⇒ Object 



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# File 'lib/wu/geo/geolocated.rb', line 90

def lng_lat        ; [longitude, latitude] ; end

#packed_qk ⇒ Object

the packed quadkey is the integer formed by interleaving the bits of tile_x with tile_y:

  tile_x      58  binary  0  0  1  1  1  0  1  0
  tile_y      105 binary 0  1  1  0  1  0  0  1
  interleaved     binary 00 10 11 01 11 00 01 10
  quadkey                 0  2  3  1  3  0  1  2 #  "02313012"

(see quadkey for more.)

At zoom level 15, the packed quadkey is a 30-bit unsigned integer – meaning you can store it in a pig int; for languages with an unsigned int type, you can go to zoom level 16 before you have to use a less-efficient type. Zoom level 15 has a resolution of about one tile per kilometer (about 1.25 km/tile near the equator; 0.75 km/tile at London’s latitude). It takes 1 billion tiles to tile the world at that scale. Ruby’s integer type goes up to 60 bits, enough for any practical zoom level.



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# File 'lib/wu/geo/geolocated.rb', line 75

def packed_qk      ; Wukong::Geolocated.tile_xy_zl_to_packed_qk(tile_x(zl), tile_y(zl), zl) ; end

#quadkey(zl) ⇒ Object

The quadkey is a string of 2-bit tile selectors for a quadtile

Interesting quadkey properties:

  • The quadkey length is its zoom level

  • To zoom out (lower zoom level, larger quadtile), just truncate the quadkey: austin at ZL=8 has quadkey “02313012”; at ZL=3, “023”

  • Nearby points typically have “nearby” quadkeys: up to the smallest tile that contains both, their quadkeys will have a common prefix. If you sort your records by quadkey, - Nearby points are nearby-ish on disk. (hello, HBase/Cassandra database owners!) This allows efficient lookup and caching of “popular” regions or repeated queries in an area. - the tiles covering a region can be covered by a limited, enumerable set of range scans. For map-reduce programmers, this leads to very efficient reducers

  • The quadkey is the bit-interleaved combination of its tile ids:

    tile_x      58  binary  0  0  1  1  1  0  1  0
tile_y      105 binary 0  1  1  0  1  0  0  1
interleaved     binary 00 10 11 01 11 00 01 10
quadkey                 0  2  3  1  3  0  1  2 #  "02313012"

Examples:

infochimps_hq = Geo::Place.receive("Infochimps HQ", -97.759003, 30.273884)
infochimps_hq.quadkey(8) # => "02313012"


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# File 'lib/wu/geo/geolocated.rb', line 55

def quadkey(zl)    ; Wukong::Geolocated.tile_xy_zl_to_quadkey(  tile_x(zl), tile_y(zl), zl) ; end

#tile_x(zl) ⇒ Integer

Returns x index of the tile this object lies on at given zoom level.

Returns:

  • (Integer) —

    x index of the tile this object lies on at given zoom level



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# File 'lib/wu/geo/geolocated.rb', line 82

def tile_x(zl)     ; tile_xf(zl).floor  ; end

#tile_xf(zl) ⇒ Float

Returns x index of the tile this object lies on at given zoom level.

Returns:

  • (Float) —

    x index of the tile this object lies on at given zoom level



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# File 'lib/wu/geo/geolocated.rb', line 78

def tile_xf(zl)    ; Wukong::Geolocated.lng_zl_to_tile_xf(longitude, zl)  ; end

#tile_xy(zl) ⇒ Float

Returns tile coordinates (x,y) for this object at given zoom level.

Returns:

  • (Float) —

    tile coordinates (x,y) for this object at given zoom level



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# File 'lib/wu/geo/geolocated.rb', line 87

def tile_xy(zl)    ; [tile_x(xl), tile_y(zl)] ; end

#tile_y(zl) ⇒ Integer

Returns y index of the tile this object lies on at given zoom level.

Returns:

  • (Integer) —

    y index of the tile this object lies on at given zoom level



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# File 'lib/wu/geo/geolocated.rb', line 84

def tile_y(zl)     ; tile_yf(zl).floor  ; end

#tile_yf(zl) ⇒ Float

Returns y index of the tile this object lies on at given zoom level.

Returns:

  • (Float) —

    y index of the tile this object lies on at given zoom level



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# File 'lib/wu/geo/geolocated.rb', line 80

def tile_yf(zl)    ; Wukong::Geolocated.lat_zl_to_tile_yf(latitude,  zl)  ; end