jnebeker / rgeo-proj4

Proj4 extension for rgeo.

rgeo-proj4

This project contains proj.4 extensions to the rgeo gem.

Documentation about proj.4 is available at http://proj4.org/.

Installation

Install PROJ

Install proj using your package manager:

Homebrew

brew install proj

Ubuntu/Debian

apt-get install libproj-dev proj-bin

Or download binaries at https://proj.org/

Note that version 3.x requires PROJ 6.2+. This should be the default on most systems, but in some cases, specific repositories will need to be added to the package manager.

Add this line to your Gemfile:

gem "rgeo-proj4"

And then execute:

$ bundle

Or install it yourself as:

$ gem install rgeo-proj4

By default, the gem looks for the Proj4 library in the following paths:

/usr/local
/usr/local/proj
/usr/local/proj4
/opt/local
/opt/proj
/opt/proj4
/opt
/usr
/Library/Frameworks/PROJ.framework/unix

If Proj4 is installed in a different location, you must provide its installation prefix directory using the --with-proj-dir option.

Usage

The rgeo-proj4 gem can be used by defining CoordSys::Proj4 objects, as a part of an RGeo::Geographic.projected_factory, or as an attribute of other factories.

RGeo::CoordSys::Proj4

This is the lowest level module to transform between coordinate systems and all of the other methods ultimately rely on this object. The object is created with a valid PROJ definition which is used to define a coordinate reference system (CRS). Note that 2 Proj4 objects need to be defined to transform between CRS's.

In addition to allowing transformations, this object can return information about the CRS.

require 'rgeo'
require 'rgeo/proj4'

# define CRS's
geography = RGeo::CoordSys::Proj4.create("EPSG:4326")
projection = RGeo::CoordSys::Proj4.create("EPSG:3857")

x,y = RGeo::CoordSys::Proj4.transform_coords(projection, geography, -8367354.015764384, 4859054.160863457, nil)

p x
# => -75.16522
p y
# => 39.95258299

Other information can be shown from the Proj4 object:

require 'rgeo'
require 'rgeo/proj4'

projection = RGeo::CoordSys::Proj4.create("EPSG:3857")
p projection.canconical_str
# => "+proj=merc +a=6378137 +b=6378137 +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0 +k=1 +units=m +nadgrids=@null +wktext +no_defs +type=crs"

p projection.auth_name
# => "EPSG:3857"

p projection.as_text
# => PROJCRS[\"WGS 84 / Pseudo-Mercator\",BASEGEOGCRS[\"WGS 84\",DATUM[\"World Geodetic System 1984\",ELLIPSOID[\"WGS 84\",6378137,298.257223563,LENGTHUNIT[\"metre\",1]]],PRIMEM[\"Greenwich\",0,ANGLEUNIT[\"degree\",0.0174532925199433]],ID[\"EPSG\",4326]],CONVERSION[\"Popular Visualisation Pseudo-Mercator\",METHOD[\"Popular Visualisation Pseudo Mercator\",ID[\"EPSG\",1024]],PARAMETER[\"Latitude of natural origin\",0,ANGLEUNIT[\"degree\",0.0174532925199433],ID[\"EPSG\",8801]],PARAMETER[\"Longitude of natural origin\",0,ANGLEUNIT[\"degree\",0.0174532925199433],ID[\"EPSG\",8802]],PARAMETER[\"False easting\",0,LENGTHUNIT[\"metre\",1],ID[\"EPSG\",8806]],PARAMETER[\"False northing\",0,LENGTHUNIT[\"metre\",1],ID[\"EPSG\",8807]]],CS[Cartesian,2],AXIS[\"easting (X)\",east,ORDER[1],LENGTHUNIT[\"metre\",1]],AXIS[\"northing (Y)\",north,ORDER[2],LENGTHUNIT[\"metre\",1]],USAGE[SCOPE[\"unknown\"],AREA[\"World - 85\xC2\xB0S to 85\xC2\xB0N\"],BBOX[-85.06,-180,85.06,180]],ID[\"EPSG\",3857]]

Projected Factory

The projected factory is a compound geographic factory that is useful for converting from lon/lat to the specified CRS.

require 'rgeo'
require 'rgeo/proj4'

factory = RGeo::Geographic.projected_factory(projection_proj4: "EPSG:3857", projection_srid: 3857)

p factory.projection_factory
# => #<RGeo::Geos::CAPIFactory srid=3857 bufres=1 flags=8>

p factory.projection_factory.proj4
# => #<RGeo::CoordSys::Proj4 "+proj=merc +a=6378137 +b=6378137 +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0 +k=1 +units=m +nadgrids=@null +wktext +no_defs +type=crs">

p factory.projection_factory.proj4.auth_name
# => "EPSG:3857"

pt = factory.point(-75.16522, 39.95258299)
p pt.projection
# => #<RGeo::Geos::CAPIPointImpl "POINT (-8367354.015764384 4859054.159411294)">

p factory.unproject(pt.projection)
# => #<RGeo::Geographic::ProjectedPointImpl "POINT (-75.16522 39.952582989999996)">

Feature::Cast

This method allows you to perform projections between more than just a lon/lat system. As long as 2 factories with valid Proj4 CRS's are defined, it can project between the CRS's.

require 'rgeo'
require 'rgeo/proj4'

geography = RGeo::Geos.factory(proj4: "EPSG:4326", srid: 4326)
projection = RGeo::Geos.factory(proj4: "EPSG:3857", srid: 3857)

p geography.proj4.auth_name
# => "EPSG:4326"
p projection.proj4.auth_name
# => "EPSG:3857"

proj_point = projection.parse_wkt("POINT (-8367354.015764384 4859054.159411294)")

geo_point = RGeo::Feature.cast(proj_point, project: true, factory: geography)
p geo_point
# => #<RGeo::Geos::CAPIPointImpl "POINT (-75.16522 39.952582989999996)">

proj_point2 = RGeo::Feature.cast(geo_point, project: true, factory: projection)

p proj_point == proj_point2
# => true

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/rgeo/rgeo-proj4. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

License

The gem is available as open source under the terms of the MIT License.

Code of Conduct

Everyone interacting in the rgeo-proj4 project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.