Simple yet useful Geo Coordinates class for Ruby
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README.md

Geo::Coord—simple geo coordinates class for Ruby

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Geo::Coord is a basic class representing [latitude, longitude] pair and incapsulating related concepts and calculations.

Features

  • Simple storage for geographical latitude & longitude pair;
  • Easily converted from/to many different representations (arrays, hashes, degrees/minutes/seconds, radians, strings with different formatting);
  • Geodesy math (distances, directions, endpoints) via precise Vincenty formula.

Reasons

Geo coordinates are, in fact, one of basic types in XXI century programming.

This gem is a (desperate) attempt to provide such a "basic" type ready to be dropped into any of Ruby code, to unify all different LatLng or Point or Location classes in existing geography and geo-aware gems for easy data exchange and natural usage.

As an independent gem, this attempt is doomed by design, but why not to try?..

Initially, I've done this work as a proposal for inclusion in Ruby's standard library, but it was not met very well. So, now I'm releasing it as a gem to be available at least for my own other projects.

You can read my initial proposal here and discussion in Ruby tracker there.

I still have a small hope it would be part of stdlib once, that's why I preserve the style of specs (outdated rspec, but compatible with mspec used for standard library) and docs (yard in RDoc-compatibility mode).

Installation

Now when it is a gem, just do your usual gem install geo_coord or add gem "geo_coord", require: "geo/coord" to your Gemfile.

Usage

Creation

require 'geo/coord'

# From lat/lng pair:
g = Geo::Coord.new(50.004444, 36.231389)
# => #<Geo::Coord 50°0'16"N 36°13'53"E>

# Or using keyword arguments form:
g = Geo::Coord.new(lat: 50.004444, lng: 36.231389)
# => #<Geo::Coord 50°0'16"N 36°13'53"E>

# Keyword arguments also allow creation of Coord from components:
g = Geo::Coord.new(latd: 50, latm: 0, lats: 16, lath: 'N', lngd: 36, lngm: 13, lngs: 53, lngh: 'E')
# => #<Geo::Coord 50°0'16"N 36°13'53"E>

For parsing API responses you'd like to use from_h, which accepts String and Symbol keys, any letter case, and knows synonyms (lng/lon/longitude):

g = Geo::Coord.from_h('LAT' => 50.004444, 'LON' => 36.231389)
# => #<Geo::Coord 50°0'16"N 36°13'53"E>

For math, you'd probably like to be able to initialize Coord with radians rather than degrees:

g = Geo::Coord.from_rad(0.8727421884291233, 0.6323570306208558)
# => #<Geo::Coord 50°0'16"N 36°13'53"E>

There's also family of string parsing methods, with different applicability:

# Tries to parse (lat, lng) pair:
g = Geo::Coord.parse_ll('50.004444, 36.231389')
# => #<Geo::Coord 50°0'16"N 36°13'53"E>

# Tries to parse degrees/minutes/seconds:
g = Geo::Coord.parse_dms('50° 0′ 16″ N, 36° 13′ 53″ E')
# => #<Geo::Coord 50°0'16"N 36°13'53"E>

# Tries to do best guess:
g = Geo::Coord.parse('50.004444, 36.231389')
# => #<Geo::Coord 50°0'16"N 36°13'53"E>
g = Geo::Coord.parse('50° 0′ 16″ N, 36° 13′ 53″ E')
# => #<Geo::Coord 50°0'16"N 36°13'53"E>

# Allows user to provide pattern:
g = Geo::Coord.strpcoord('50.004444, 36.231389', '%lat, %lng')
# => #<Geo::Coord 50°0'16"N 36°13'53"E>

Pattern language description

Examining the object

Having Coord object, you can get its properties:

g = Geo::Coord.new(50.004444, 36.231389)
g.lat # => 50.004444
g.latd # => 50 -- latitude degrees
g.lath # => N -- latitude hemisphere
g.lngh # => E -- longitude hemishpere
g.phi  # => 0.8727421884291233 -- longitude in radians
g.latdms # => [50, 0, 15.998400000011316, "N"]
# ...and so on

Formatting and converting

g.to_s              # => "50°0'16\"N 36°13'53\"E"
g.to_s(dms: false)  # => "50.004444,36.231389"
g.strfcoord('%latd°%latm′%lats″%lath %lngd°%lngm′%lngs″%lngh')
# => "50°0′16″N 36°13′53″E"

g.to_h(lat: 'LAT', lng: 'LON') # => {'LAT'=>50.004444, 'LON'=>36.231389}

Geodesy math

kharkiv = Geo::Coord.new(50.004444, 36.231389)
kyiv = Geo::Coord.new(50.45, 30.523333)

kharkiv.distance(kyiv) # => 410211.22377421556
kharkiv.azimuth(kyiv) # => 279.12614358262067
kharkiv.endpoint(410_211, 280) # => #<Geo::Coord 50°30'22"N 30°31'53"E>

Full API Docs

Design decisions

While designing Geo library, my reference point was standard Time class (and, to lesser extent, Date/DateTime). It has these responsibilities:

  • stores data in simple internal form;
  • helps to parse and format data to and from strings;
  • provides easy access to logical components of data;
  • allows most simple and unambiguous calculations.

Namespace name: The gem takes pretty short and generic top-level namespace name Geo, but creates only one class inside it: Geo::Coord.

Main type name: as far as I can see, there's no good singular name for (lat, lng) pair concept. In different libraries, there can be seen names like LatLng, or Location, or Point; and in natural language just "coordinates" used frequently. I propose the name Coord, which is pretty short, easy to remember, demonstrates intentions (and looks like singular, so you can have "one coord object" and "array of coords", which is not 100% linguistically correct, yet convenient). Alternative Point name seems to be too ambiguous, being used in many contexts.

Geo::Coord object is immutable, there's no semantical sense in location.latitude = ... or something like this.

Units: Geo calculations (just like Time calculations) provide no units options, just returning numbers measured in "default" units: metres for distances (as they are SI unit) and degrees for azimuth. Latitude and longitude are stored in degrees, but radians values accessors are provided (being widely used in geodesy math).

Internal storage: Since ver 0.0.2, latitude and longitude stored internally as an instances of BigDecimal. While having some memory and performance downsides, this datatype provides correctness of conversions between floating point & deg-min-sec representations:

# 33.3 should be 33°18'00"
# Float:
33.3 * 60 % 60 # => 17.999999999999773 minutes
# BigDecimal
BigDecimal(33.3, 10) * 60 % 60 # => 0.18e2

All coordinates and calculations are thought to be in WGS 84 coordinates reference system, being current standard for maps and GPS.

There's introduced a concept of globe used internally for calculations. Only generic (sphere) and Earth globes are implemented, but for 2010th I feel like the current design of basic types should take in consideration possibility of writing Ruby scripts for Mars maps analysis. Only one geodesy formula is implemented (Vincenty, generally considered one of the most precise), as for standard library class it considered unnecessary to provide a user with geodesy formulae options.

No map projection math was added into the current gem, but it may be a good direction for further work. No elevation data considered either.

Author

Victor Shepelev

License

MIT.