Class: GD::GIS::Basemap

Inherits:
Object
  • Object
show all
Defined in:
lib/gd/gis/basemap.rb

Overview

Fetches and manages raster basemap tiles using the XYZ Web Mercator tiling scheme.

A Basemap is responsible for:

  • Converting geographic coordinates to tile coordinates

  • Downloading raster tiles from public tile providers

  • Caching tiles on disk

  • Exposing pixel origins for map composition

All tiles are assumed to be 256×256 pixels.

Examples:

Fetch tiles for a bounding box

bbox = [-3.8, 40.3, -3.6, 40.5] # west, south, east, north
basemap = GD::GIS::Basemap.new(12, bbox, :carto_light)
tiles, origin_x, origin_y = basemap.fetch_tiles

Constant Summary collapse

TILE_SIZE =

Tile size in pixels (Web Mercator standard)

256

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(zoom, bbox, provider = :carto_light) ⇒ Basemap

Creates a new basemap tile source.

Parameters:

  • zoom (Integer) —

    zoom level

  • bbox (Array<Float>) —

    bounding box [west, south, east, north]

  • provider (Symbol) (defaults to: :carto_light) —

    tile provider/style



39
40
41
42
43
 
# File 'lib/gd/gis/basemap.rb', line 39

def initialize(zoom, bbox, provider = :carto_light)
  @zoom = zoom
  @bbox = bbox
  @provider = provider
end

Instance Attribute Details

#origin_x ⇒ Integer (readonly)

Returns pixel X origin of the basemap.

Returns:

  • (Integer) —

    pixel X origin of the basemap



29
30
31
 
# File 'lib/gd/gis/basemap.rb', line 29

def origin_x
  @origin_x
end

#origin_y ⇒ Integer (readonly)

Returns pixel Y origin of the basemap.

Returns:

  • (Integer) —

    pixel Y origin of the basemap



32
33
34
 
# File 'lib/gd/gis/basemap.rb', line 32

def origin_y
  @origin_y
end

Instance Method Details

#fetch_tiles ⇒ Array

Downloads all tiles required to cover the bounding box.

Tiles are cached on disk under ‘tmp/tiles`.

Returns:

  • (Array) —

    • tiles [Array<Array(Integer, Integer, String)>] list of [x, y, file_path]

    • origin_x [Integer] pixel X origin

    • origin_y [Integer] pixel Y origin

Raises:

  • (RuntimeError) —

    if a tile cannot be fetched



167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
 
# File 'lib/gd/gis/basemap.rb', line 167

def fetch_tiles
  west, south, east, north = @bbox

  x_min = lon2tile(west)
  x_max = lon2tile(east)
  y_min = lat2tile(north)
  y_max = lat2tile(south)

  @x_min = x_min
  @y_min = y_min

  @origin_x = x_min * TILE_SIZE
  @origin_y = y_min * TILE_SIZE

  FileUtils.mkdir_p("tmp/tiles")

  tiles = []

  (x_min..x_max).each do |x|
    (y_min..y_max).each do |y|
      path = nil

      if File.exist?("tmp/tiles/#{@provider}_#{@zoom}_#{x}_#{y}.png") ||
         File.exist?("tmp/tiles/#{@provider}_#{@zoom}_#{x}_#{y}.jpg")
        path = if File.exist?("tmp/tiles/#{@provider}_#{@zoom}_#{x}_#{y}.png")
                 "tmp/tiles/#{@provider}_#{@zoom}_#{x}_#{y}.png"
               else
                 "tmp/tiles/#{@provider}_#{@zoom}_#{x}_#{y}.jpg"
               end
      else

        uri = URI(url(@zoom, x, y, @provider))

        Net::HTTP.start(uri.host, uri.port, use_ssl: true) do |http|
          req = Net::HTTP::Get.new(uri)
          req["User-Agent"] = "libgd-gis/0.1 (Ruby)"

          res = http.request(req)
          raise "Tile fetch failed #{res.code}" unless res.code == "200"

          content_type = res["content-type"]

          ext =
            if content_type&.include?("png")
              "png"
            elsif content_type&.include?("jpeg") || content_type&.include?("jpg")
              "jpg"
            else
              raise "Unsupported tile type: #{content_type}"
            end

          path = "tmp/tiles/#{@provider}_#{@zoom}_#{x}_#{y}.#{ext}"
          File.binwrite(path, res.body)
        end
      end

      tiles << [x, y, path]
    end
  end

  [tiles, x_min, y_min]
end

#lat2tile(lat) ⇒ Integer

Converts latitude to tile Y coordinate.

Parameters:

  • lat (Float) —

    latitude in degrees

Returns:

  • (Integer) —

    tile Y coordinate



151
152
153
154
 
# File 'lib/gd/gis/basemap.rb', line 151

def lat2tile(lat)
  rad = lat * Math::PI / 180
  ((1 - (Math.log(Math.tan(rad) + (1 / Math.cos(rad))) / Math::PI)) / 2 * (2**@zoom)).floor
end

#lon2tile(lon) ⇒ Integer

Converts longitude to tile X coordinate.

Parameters:

  • lon (Float) —

    longitude in degrees

Returns:

  • (Integer) —

    tile X coordinate



143
144
145
 
# File 'lib/gd/gis/basemap.rb', line 143

def lon2tile(lon)
  ((lon + 180.0) / 360.0 * (2**@zoom)).floor
end

#url(z, x, y, style = :osm) ⇒ String

Builds a tile URL for a given provider and tile coordinate.

Parameters:

  • z (Integer) —

    zoom level

  • x (Integer) —

    tile X coordinate

  • y (Integer) —

    tile Y coordinate

  • style (Symbol) (defaults to: :osm) —

    tile style/provider

Returns:

  • (String) —

    tile URL

Raises:

  • (RuntimeError) —

    if the provider is unknown



53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
 
# File 'lib/gd/gis/basemap.rb', line 53

def url(z, x, y, style = :osm)
  case style

  # ==============================
  # OpenStreetMap
  # ==============================
  when :osm
    "https://tile.openstreetmap.org/#{z}/#{x}/#{y}.png"

  when :osm_hot
    "https://tile.openstreetmap.fr/hot/#{z}/#{x}/#{y}.png"

  when :osm_fr
    "https://a.tile.openstreetmap.fr/osmfr/#{z}/#{x}/#{y}.png"

  # ==============================
  # CARTO
  # ==============================
  when :carto_light
    "https://a.basemaps.cartocdn.com/light_all/#{z}/#{x}/#{y}.png"

  when :carto_light_nolabels
    "https://a.basemaps.cartocdn.com/light_nolabels/#{z}/#{x}/#{y}.png"

  when :carto_dark
    "https://a.basemaps.cartocdn.com/dark_all/#{z}/#{x}/#{y}.png"

  when :carto_dark_nolabels
    "https://a.basemaps.cartocdn.com/dark_nolabels/#{z}/#{x}/#{y}.png"

  # ==============================
  # ESRI / ArcGIS (Satellite, terrain, hybrid)
  # ==============================
  when :esri_satellite
    "https://services.arcgisonline.com/ArcGIS/rest/services/World_Imagery/MapServer/tile/#{z}/#{y}/#{x}"

  when :esri_streets
    "https://services.arcgisonline.com/ArcGIS/rest/services/World_Street_Map/MapServer/tile/#{z}/#{y}/#{x}"

  when :esri_terrain
    "https://services.arcgisonline.com/ArcGIS/rest/services/World_Topo_Map/MapServer/tile/#{z}/#{y}/#{x}"

  # ==============================
  # STAMEN 503
  # ==============================
  when :stamen_toner
    "https://stamen-tiles.a.ssl.fastly.net/toner/#{z}/#{x}/#{y}.png"

  when :stamen_toner_lite
    "https://stamen-tiles.a.ssl.fastly.net/toner-lite/#{z}/#{x}/#{y}.png"

  when :stamen_terrain
    "https://stamen-tiles.a.ssl.fastly.net/terrain/#{z}/#{x}/#{y}.png"

  when :stamen_watercolor
    "https://stamen-tiles.a.ssl.fastly.net/watercolor/#{z}/#{x}/#{y}.jpg"

  # ==============================
  # OpenTopoMap
  # ==============================
  when :topo
    "https://a.tile.opentopomap.org/#{z}/#{x}/#{y}.png"

  # ==============================
  # Wikimedia 403
  # ==============================
  when :wikimedia
    "https://maps.wikimedia.org/osm-intl/#{z}/#{x}/#{y}.png"

  # ==============================
  # OpenRailwayMap
  # ==============================
  when :railway
    "https://tiles.openrailwaymap.org/standard/#{z}/#{x}/#{y}.png"

  # ==============================
  # CyclOSM
  # ==============================
  when :cyclosm
    "https://a.tile-cyclosm.openstreetmap.fr/cyclosm/#{z}/#{x}/#{y}.png"

  else
    raise "Unknown basemap style: #{style}"
  end
end