Geo

Geospatial primitives, algorithms, and utilities for Crystal.

Installation

Add this to your application's shard.yml:

dependencies:
  geo:
    github: geocrystal/geo

Run shards install

Usage

A Geo::Coord is a point in geographical coordinates: latitude and longitude.

require "geo"

c = Geo::Coord.new(50.004444, 36.231389)

c.strfcoord(%{%latd %latm' %0.1lats" %lath, %lngd %lngm' %0.1lngs" %lngh})
# => "50 0' 16.0" N, 36 13' 53.0" E"

c.strfcoord("%lat,%lng")
# => "-50.004444,-36.231389"

c.to_s
# => "50°0'16"N 36°13'53"E"

pos = Geo::Coord.new(50.004444, 36.231389)

pos.geohash
# => "ubcu2rnbuxcx"

pos.geohash(5)
# => "ubcu2"

Polygon

A polygon represents an area enclosed by a closed path (or loop), which is defined by a series of coordinates.

require "geo"

pos1 = Geo::Coord.new(45.3142533036254, -93.47527313511819)
pos2 = Geo::Coord.new(45.31232182518015, -93.34893036168069)
pos3 = Geo::Coord.new(45.23694281999268, -93.35167694371194)
pos4 = Geo::Coord.new(45.23500870841669, -93.47801971714944)

polygon = Geo::Polygon.new([pos1, pos2, pos3, pos4])

The Polygon in the example above consists of four sets of Geo::Coord coordinates, but notice that the first and last sets define the same location, which completes the loop. In practice, however, since polygons define closed areas, you don't need to specify the last set of coordinates. Ot will automatically complete the polygon by connecting the last location back to the first location.

The following example is identical to the previous one, except that the last Geo::Coord is omitted:

require "geo"

pos1 = Geo::Coord.new(45.3142533036254, -93.47527313511819)
pos2 = Geo::Coord.new(45.31232182518015, -93.34893036168069)
pos3 = Geo::Coord.new(45.23694281999268, -93.35167694371194)

polygon = Geo::Polygon.new([pos1, pos2, pos3])

Additional actions:

coord_inside = Geo::Coord.new(45.27428243796789, -93.41648483416066)
coord_outside = Geo::Coord.new(45.45411010558687, -93.78151703160256)

polygon.contains?(coord_inside)  # => true
polygon.contains?(coord_outside) # => false

polygon.centroid # => Geo::Coord(@lat=45.27463866133501, @lng=-93.41400121829719)

Additionally you can initialize polygon as convex hull from coordinates of points.

points = [
  {1.0, 1.0},
  {1.0, 0.0},
  {1.0, -1.0},
  {0.0, -1.0},
  {-1.0, -1.0},
  {-1.0, 0.0},
  {-1.0, 1.0},
  {0.0, 1.0},
  {0.0, 0.0},
].map { |point| Geo::Coord.new(point[0], point[1]) }

polygon = Geo::Polygon.new(points, convex_hull: true)
polygon.coords
# => {-1.0, -1.0}, {1.0, -1.0}, {1.0, 1.0}, {-1.0, 1.0}, {-1.0, -1.0}

The convex hull is computed using the convex_hull library.

Formatting

Geo::Coord#strfcoord formats coordinates according to directives.

Each directive starts with % and can contain some modifiers before its name.

Acceptable modifiers:

• unsigned integers: none;
• signed integers: + for mandatory sign printing;
• floats: same as integers and number of digits modifier, like 0.3.

List of directives:

Directive	Description
%lat	Full latitude, floating point, signed
%latds	Latitude degrees, integer, signed
%latd	Latitude degrees, integer, unsigned
%latm	Latitude minutes, integer, unsigned
%lats	Latitude seconds, floating point, unsigned
%lath	Latitude hemisphere, "N" or "S"
%lng	Full longitude, floating point, signed
%lngds	Longitude degrees, integer, signed
%lngd	Longitude degrees, integer, unsigned
%lngm	Longitude minutes, integer, unsigned
lngs	Longitude seconds, floating point, unsigned
%lngh	Longitude hemisphere, "E" or "W"

Examples:

g = Geo::Coord.new(50.004444, 36.231389)
g.strfcoord('%+lat, %+lng')
# => "+50.004444, +36.231389"
g.strfcoord("%latd°%latm'%lath -- %lngd°%lngm'%lngh")
# => "50°0'N -- 36°13'E"

strfcoord handles seconds rounding implicitly:

pos = Geo::Coord.new(0.033333, 91.333333)
pos.strfcoord('%latd %latm %0.5lats') # => "0 1 59.99880"
pos.strfcoord('%latd %latm %lats')  # => "0 2 0"

Calculate distances between two coords

Haversine formula from haversine shard is used.

require "geo"
require "geo/distance"

london = Geo::Coord.new(51.500153, -0.126236)
new_york = Geo::Coord.new(40.714268, -74.005974)

new_york.distance(london).to_kilometers
# => 5570.4744596620685

Calculates the location of a destination coord

require "geo"
require "geo/distance"

point = Geo::Coord.new(39, -75)

point.destination(5000, 90, :kilometers)
# Geo::Coord(@lat=26.440010707631124, @lng=-22.885355549364313)

Contributing

1. Fork it (https://github.com/geocrystal/geo/fork)
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

Contributors

• Anton Maminov - creator and maintainer