Some geospatial ruby libraries lightning talk presented at Leeds Ruby Thing, April 2016

1. Some Ruby Geospatial Libraries

2. Rosemary
require 'rosemary'
client = Rosemary::BasicAuthClient.new
('osm_user_name', 'password')
api = Rosemary::Api.new(client)
changeset = api.create_changeset("Add
postbox")
node = Rosemary::Node.new(lat, lon)
node.add_tags({"amenity"=>"postbox"})
api.save(node, changeset)
api.close_changeset(changeset)

3. Overpass API

4. require 'overpass_api_ruby'
pub_query = "<union>
<query type='relation'>
<has­kv k="amenity" v="pub"/>
</query>
</union>"
Options ={:bbox => {:s =>­34.7,:n => ­34.2,
:w => ­58.53, :e => ­58.33},
:timeout => 900,
:element_limit => 1073741824,
:json => true}
overpass = OverpassAPI.new(options)
result_hash = overpass.query(pub_query)

6. GEOS
def buffer(feature, radius, min_radius=0.0)
wkb_writer = Geos::WkbWriter.new
wkb_reader = Geos::WkbReader.new
geom = wkb_reader.read_hex(feature.geometry)
buffer_geom = geom.buffer(radius)
if min_radius != 0.0
hole_geom = geom.buffer(min_radius)
buffer_geom = buffer_geom.difference(hole_geom)
end
feature.geometry = wkb_writer.write_hex buffer_geom
feature
end

8. GDAL / OGR
● https://github.com/zhm/gdal-ruby
Gdal::Ogr.create_geometry_from_wkt('POINT (30 10)')
raster = Gdal::Gdal.open(filename)
dx = raster.RasterXSize
dy = raster.RasterYSize
x0, x_res, x_skew, y0, y_skew, y_res =
raster.get_geo_transform

9. RGeo
https://github.com/rgeo/rgeo
factory = Rgeo::Cartesian.factory
point1 = factory.point(1, 0)
point2 = factory.point(1, 4)
point3 = factory.point(­2, 0)
point2.distance(point3) # => 5.0
line_string1 = factory.line_string([point1, point2, point3])
line_string1.num_points # => 3
line_string1.point_n(0) == point1 # => true
line_string1.end_point == point3 # => true

10. PostGIS / postgres
https://github.com/rgeo/activerecord-postgis-adapter
create_table :my_spatial_table do |t|
t.column :shape1, :geometry
t.geometry :shape2
t.line_string :path, srid: 3785
t.st_point :lonlat, geographic: true
t.st_point :lonlatheight, geographic: true, has_z: true
end

11. PostGIS / postgres
bbox_polygon =
Polygon.from_coordinates([bbox_coords], 4326).as_ewkt
Model.where(ST_Within(bbox_geom,
ST_GeomFromText('#{bbox_polygon}'))")

12. map = Mapnik::Map.new do |m|
m.background = Mapnik::Color.new('#777') # A grey background
# Use the Google mercator projection
m.srs = Mapnik::Tile::DEFAULT_OUTPUT_PROJECTION
# Add a layer to the map
m.layer 'countries' do |l|
l.style do |s|
# Add a rule to the style (this one is a default rule)
s.rule do |default|
default.fill = Mapnik::Color.new('#880000')
end
end
l.srs = "+proj=latlong +datum=WGS84" # set the srs of the layer
l.datasource = Mapnik::Datasource.create :type => 'shape',
:file => "myshapefile.shp"
end
end
map.zoom_to_box(map.layers.first.envelope)
map.render_to_file('my_map.png')
Ruby Mapnik