Database

Starting with version 6, Proj stores its reference data (datums, ellipsoids, prime meridians, coordinate systems, units, etc.) in a SQLite file called proj.db. The Database class provides access to this data.

Every Context has an associated database accessible via Context#database.

Querying

Authorities

List the authorities available in the database:

context = Proj::Context.new
authorities = context.database.authorities
# ["EPSG", "IGNF", "NKG", "OGC", "PROJ", ...]

CRS Information

Enumerate CRS entries, optionally filtered by authority:

crs_list = context.database.crs_info("EPSG")
crs_list.each do |info|
  puts "#{info.auth_name}:#{info.code} - #{info.name} (#{info.type})"
end

Authority Codes

Get all codes for a given object type under an authority:

codes = context.database.codes("EPSG", :PJ_TYPE_GEOGRAPHIC_2D_CRS)

Units

List available units, optionally filtered by authority or category:

# All units
units = context.database.units

# Linear units only
linear_units = context.database.units(category: "linear")

# Get a specific unit
metre = context.database.unit("EPSG", "9001")
puts "#{metre.name}: #{metre.conv_factor}"

Metadata

Query database metadata:

version = context.database.metadata("EPSG.VERSION")
date = context.database.metadata("EPSG.DATE")

Grids

Look up grid information:

grid = context.database.grid("us_noaa_alaska.tif")

Celestial Bodies

List celestial bodies known to the database:

bodies = context.database.celestial_bodies

Database Path

By default, Proj finds proj.db automatically. You can override the path:

context.database.path = "/custom/path/to/proj.db"

Or set the PROJ_DATA environment variable before launching Ruby (see Configuration).