GitHub - JuliaGeo/Proj.jl: Julia wrapper for the PROJ cartographic projections library (original) (raw)

Proj.jl

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A simple Julia wrapper around the PROJcartographic projections library. This package has been renamed from Proj4.jl to Proj.jl.

Quickstart, based on the PROJ docs:

using Proj

Proj.jl implements the CoordinateTransformations.jl API.

A Proj.Transformation needs the source and target coordinate reference systems (CRS),

or a single pipeline.

trans = Proj.Transformation("EPSG:4326", "+proj=utm +zone=32 +datum=WGS84")

The CRS can be a string or the CRS type, which also interfaces with GeoFormatTypes.jl.

Once created, you can call this object to transform points.

The result will be a tuple of Float64s, of length 2, 3 or 4 depending on the input length.

The 3rd coordinate is elevation (default 0), and the 4th is time (default Inf).

Here the (latitude, longitude) of Copenhagen is entered

trans(55, 12)

-> (691875.632137542, 6.098907825129169e6)

Passing coordinates as a single tuple or vector also works.

Note that above the latitude is passed first, because that is the axis order that the

EPSG mandates. If you want to pass in (longitude, latitude) / (x, y), you can set the

always_xy keyword to true. For more info see https://proj.org/faq.html#why-is-the-axis-ordering-in-proj-not-consistent

trans = Proj.Transformation("EPSG:4326", "+proj=utm +zone=32 +datum=WGS84", always_xy=true)

now we input (longitude, latitude), and get the same result as above

trans(12, 55)

-> (691875.632137542, 6.098907825129169e6)

using inv we can reverse the direction, compose can combine two transformations in one

inv(trans)(691875.632137542, 6.098907825129169e6) == (12, 55)

Note that, as described in https://proj.org/resource_files.html, PROJ has the capability to use remote grids for transformations that need them. Unless you have manually set the environment variable PROJNETWORK=ON or changed proj.ini, networking is disabled by default. To enable from Julia, run Proj.enable_network!().Proj.network_enabled() can be used to check the setting, and Proj.with_network provides a way to temporarily enable or disable it in a do-block. Note that it needs to be set before creating a transformation, otherwise it will have no effect.

API documentation for the underlying C API may be found here:https://proj.org/development/reference/index.html