Coordinate reference systems in Cartopy¶
The cartopy.crs.CRS
class is the very core of cartopy, all coordinate reference systems
in cartopy have CRS
as a parent class, meaning all projections have
the interface described below.

class
cartopy.crs.
CRS
(proj4_params, globe=None)¶ Defines a Coordinate Reference System using proj.4.
 proj4_params : iterable of keyvalue pairs
 The proj4 parameters required to define the desired CRS.
The parameters should not describe the desired elliptic model,
instead create an appropriate Globe instance. The
proj4_params
parameters will override any parameters that the Globe defines.  globe :
 If omitted, the default Globe instance will be created.
See
Globe
for details.
Globe
instance, optional
as_geocentric
()¶ Returns a new Geocentric CRS with the same ellipse/datum as this CRS.

as_geodetic
()¶ Returns a new Geodetic CRS with the same ellipse/datum as this CRS.

transform_point
(x, y, src_crs)¶ Transform the given float64 coordinate pair, in the given source coordinate system (
src_crs
), to this coordinate system.Args:
x  the x coordinate, in
src_crs
coordinates, to transformy  the y coordinate, in
src_crs
coordinates, to transform src_crs  instance of
CRS
that represents the coordinate system of
x
andy
.
 src_crs  instance of
 trap  Whether proj.4 errors for “latitude or longitude exceeded limits” and
“tolerance condition error” should be trapped.
Returns:
(x, y)  in this coordinate system

transform_points
(src_crs, x, y[, z])¶ Transform the given coordinates, in the given source coordinate system (
src_crs
), to this coordinate system.Args:
 src_crs  instance of
CRS
that represents the coordinate system of
x
,y
andz
.
 src_crs  instance of
 x  the x coordinates (array), in
src_crs
coordinates, to transform. May be 1 or 2 dimensional.
 x  the x coordinates (array), in
 y  the y coordinates (array), in
src_crs
coordinates, to transform
 y  the y coordinates (array), in
 z  (optional) the z coordinates (array), in
src_crs
coordinates, to transform.
 z  (optional) the z coordinates (array), in
 Returns:
 Array of shape
x.shape + (3, )
in this coordinate system.

transform_vectors
(src_crs, x, y, u, v)¶ Transform the given vector components, with coordinates in the given source coordinate system (
src_crs
), to this coordinate system. The vector components must be given relative to the source coordinate system (grid eastward and grid northward).Args:
 src_crs:
The
CRS
that represents the coordinate system the vectors are defined in.
 x, y:
The x and y coordinates, in the source CRS coordinates, where the vector components are located. May be 1 or 2 dimensional, but must have matching shapes.
 u, v:
The grid eastward and grid northward components of the vector field respectively. Their shape must match the shape of the x and y coordinates.
Returns:
 ut, vt:
The transformed vector components.
Note
The algorithm used to transform vectors is an approximation rather than an exact transform, but the accuracy should be good enough for visualization purposes.
The Globe
class is used to encapsulate the underlying sphere or ellipsoid of any cartopy CRS.
All CRSs have an associated Globe
, though often it is just the default Globe
which represents the reference ellipsoid (i.e. “wgs84”).

class
cartopy.crs.
Globe
(datum=None, ellipse='WGS84', semimajor_axis=None, semiminor_axis=None, flattening=None, inverse_flattening=None, towgs84=None)¶ Defines an ellipsoid and, optionally, how to relate it to the real world.
Keywords:
 datum  Proj4 “datum” definiton. Default to no datum.
 ellipse  Proj4 “ellps” definiton. Default to ‘WGS84’.
 semimajor_axis  Semimajor axis of the spheroid / ellipsoid.
 semiminor_axis  Semiminor axis of the ellipsoid.
 flattening  Flattening of the ellipsoid.
 inverse_flattening  Inverse flattening of the ellipsoid.
 towgs84  Passed through to the Proj4 definition.
 nadgrids  Passed through to the Proj4 definition.
The most common CRS
subclass is itself another abstract class;
the cartopy.crs.Projection
class represents a 2 dimensional coordinate system
which could be drawn directly as a map (i.e. on a flat piece of paper). Projection
is the parent class of
all projections in the Cartopy projection list.

class
cartopy.crs.
Projection
[source]¶ Defines a projected coordinate system with flat topology and Euclidean distance.
 proj4_params : iterable of keyvalue pairs
 The proj4 parameters required to define the desired CRS.
The parameters should not describe the desired elliptic model,
instead create an appropriate Globe instance. The
proj4_params
parameters will override any parameters that the Globe defines.  globe :
 If omitted, the default Globe instance will be created.
See
Globe
for details.
Globe
instance, optional
project_geometry
(geometry, src_crs=None)[source]¶ Projects the given geometry into this projection.
Parameters:  geometry – The geometry to (re)project.
 src_crs – The source CRS, or geodetic CRS if None.
Return type: Shapely geometry.
If src_crs is None, the source CRS is assumed to be a geodetic version of the target CRS.

quick_vertices_transform
(vertices, src_crs)[source]¶ Where possible, return a vertices array transformed to this CRS from the given vertices array of shape
(n, 2)
and the source CRS.Important
This method may return None to indicate that the vertices cannot be transformed quickly, and a more complex geometry transformation is required (see
cartopy.crs.Projection.project_geometry()
).
There are a few nonProjection
subclasses. These represent
coordinate reference systems which are 3 dimensional and could not be drawn directly on a piece of paper.

class
cartopy.crs.
Geodetic
(globe=None)¶ Defines a latitude/longitude coordinate system with spherical topology, geographical distance and coordinates are measured in degrees.
Kwargs:
 globe  A
cartopy.crs.Globe
. Defaults to a “WGS84” datum.
 globe  A

class
cartopy.crs.
Geocentric
(globe=None)¶ Defines a Geocentric coordinate system, where x, y, z are Cartesian coordinates from the center of the Earth.
Kwargs:
 globe  A
cartopy.crs.Globe
. Defaults to a “WGS84” datum.
 globe  A

class
cartopy.crs.
RotatedGeodetic
(pole_longitude, pole_latitude, central_rotated_longitude=0.0, globe=None)[source]¶ Defines a rotated latitude/longitude coordinate system with spherical topology and geographical distance.
Coordinates are measured in degrees.
Create a RotatedGeodetic CRS.
The class uses proj4 to perform an ob_tran operation, using the pole_longitude to set a lon_0 then performing two rotations based on pole_latitude and central_rotated_longitude. This is equivalent to setting the new pole to a location defined by the pole_latitude and pole_longitude values in the GeogCRS defined by globe, then rotating this new CRS about it’s pole using the central_rotated_longitude value.
Args:
pole_longitude  Pole longitude position, in unrotated degrees.
pole_latitude  Pole latitude position, in unrotated degrees.
 central_rotated_longitude  Longitude rotation about the new
pole, in degrees.
Kwargs:
 globe  An optional
cartopy.crs.Globe
. Defaults to a “WGS84” datum.
 globe  An optional
There is also a function for calling epsg.io with a specified code, returning the corresponding cartopy projection, see below.

cartopy.crs.
epsg
(code)[source]¶ Return the projection which corresponds to the given EPSG code.
The EPSG code must correspond to a “projected coordinate system”, so EPSG codes such as 4326 (WGS84) which define a “geodetic coordinate system” will not work.
Note
The conversion is performed by querying https://epsg.io/ so a live internet connection is required.