terragona

Create polygons from GeoNames places or other sources. This means: Create concave polygons using, i.e., geonames places and store them in a postgres/postgis database. See ST_Concave_Hull.

So, am I saying you can get the geometries of all places magically? Sort of... As you can see, the results are not very accurate. But they are interesting.

gem install terragona

or add gem 'terragona' to your Gemfile

• Classes API and Dump are now nested inside a Geonames class.

First, create a db in postgres and install the postgis extension.

Right now, as sources you can use:

• GeoNames API, with the Terragona::Geonames::API class,
• A Geonames dump, (Terragona::Geonames::Dump class) and specify the dump file path in opts.
• A hash (actually an array of hashes) (Terragona::Geonames::FromHash class)
• A CSV (Terragona::CSVParser class) (with headers: name,x,y)

The API is faster but less accurate than the dump (max 1000 points per request). The dump is more accurate but much slower (please, use country dumps, not the world dump: it's to big -~9 million points- and could take lots of time.). For example: with the API, the Italy polygon is drawn using 1000 points. With the dump, the input is ~95.000 points. You can use the max_points option to limit this number.

The slow part of the process is when points are filtered: the ones that are isolated are discarded. This has to be refactored.

Besides the source of the points, options target_percent and max_distance_ratio control the shape of the polygons. See the options.

With API

require 'terragona'

opts = {...}
countries=[{:name=>'Argentina',:fcode=>'PCLI',:country=>'AR'},
           {:name=>'Uruguay',:fcode=>'PCLI',:country=>'UY'}]

terragona = Terragona::Geonames::API.new(opts)
terragona.create_polygons_family(countries, 'countries', 'countries_subdivisions')

With Dump, and using returned children places

require 'terragona'

opts={
	:default_country=>'IT',
	:target_percent=> 0.85,
	:max_distance_ratio=>1.6,
	:db_username=>'mydbuser',
	:db_password=>'mydbpsswd',
	:db_name=>'mydb',
	:dump=>'/path/to/dump/IT.txt'}

italy=[{:name=>'Italy',:fcode=>'PCLI'}]

terragona = Terragona::Geonames::Dump.new(opts)
result = terragona.create_polygons_family(italy,'italy','italian_regions')

italian_rest = []
result.each {|r|
	italian_rest.concat(r[:children_places])
}
terragona.create_polygons_family(italian_rest,'province','comuni')

With the FromHash class

require 'terragona'

my_hash = [{:name=>'some_tag',:y=>some_lat,:x=>some_lon},
           {:name=>'some_tag',:y=>some_lat,:x=>some_lon},
           ...]

opts={
	:target_percent=> 0.85,
	:max_distance_ratio=>1.6,
	:db_username=>'mydbuser',
	:db_password=>'mydbpsswd',
	:db_name=>'mydb',
	:hash=>my_hash}

italy=[] #Don't need input but the hash option.

terragona = Terragona::FromHash.new(opts)
terragona.create_polygons_family(italy,'italy','italian_regions')

With the CSVParser class

require 'terragona'

# csv with headers: name,x,y
opts={
	:target_percent=> 0.85,
	:max_distance_ratio=>1.6,
	:db_username=>'mydbuser',
	:db_password=>'mydbpsswd',
	:db_name=>'mydb',
	:csv_filename=>'/path/to/csv/IT.csv'}

italy=[] #Don't need input but the csv.

terragona = Terragona::CSVParser.new(opts)
terragona.create_polygons_family(italy,'italy','italian_regions')

create_polygons(<array of places>, options)
  
create_polygons_family(<array of places>, <first order geometries table name>, <second order geometries table name>, options)

Important: With the CSVParser class the initial array of places is not used. Terragona tries to create the parent polygon using all points.

Each place in the array of places is a hash with this keys:

:name                
:fcode                   GeoNames Feature Code 
:id                      (optional)               
:children_fcode          (optional)
:country                 (optional)
:field_to_compare        (optional) (:adminCode1, :adminCode2 or :adminCode3)
:field_to_compare_value  (optional)

The methods create the tables, fill them with polygons and return the following hash:

{:children_places=>array of hashes, :points=>array of points([x,y]), :place_name=>string, :place_id=>string}

                    | distance between points are not considered. Default: 1.6.

minimal_polygon_points | Minimal number of points to build a polygon. force_homogeneity | Uses max_distance_ratio also to compare with the avg distance between points of all the other polygons of the same family level. This helps to discard outliers. The result are homogeneous polygons. dont_create_polygons | (boolean) Default: false. table | Table where polygons are saved. This option is overriden by args of create_polygons_family method.

• Check of geometry type before saving
• Use dumps as input (not only API)
• Generate multipolygon in ConcaveHull. Use some clustering algorithm.
• Improve/replace distant points algorithm. Use some clustering algorithm.

• GeoNames Country Codes
• GeoNames Feature Codes
• GeoNames Dumps download page

MIT.