CRS and projections

Cartopy provides few default projections, documented on their webpage. Cartes extends these definitions with a full set of projections as defined by the libproj C library.

Introduction example

For instance, the Lambert93 projection is the default official one in France, used for tiles by the National Geographic Institute (IGN).

from cartes.crs import Lambert93
Lambert93()

<abc.EPSG_2154 object at 0x7fbc61e1e130>

As displayed above, Lambert93 is nothing more than an alias for an EPSG specification. It is possible to obtain the same result with the following code.

from cartes.crs import EPSG_2154
EPSG_2154()

Warning

Classes are generated dynamically based on their description in the libproj library. A star import would not work here.

Valid projections at a given location

A list of valid projections is available with a call to the valid_crs functioni which accepts a string or any object implementing the __geo_interface__ protocol:

from cartes.crs import valid_crs
valid_crs("Rome, Italy")

	area	auth_name	code	deprecated	name	projection_method_name
0	Europe - between 12°E and 18°E onshore and off...	EPSG	23033	False	ED50 / UTM zone 33N	Transverse Mercator
1	Italy - onshore and offshore - east of 12°E in...	EPSG	3004	False	Monte Mario / Italy zone 2	Transverse Mercator
2	Europe - European Union (EU) countries and can...	EPSG	3034	False	ETRS89-extended / LCC Europe	Lambert Conic Conformal (2SP)
3	Europe - European Union (EU) countries and can...	EPSG	3035	False	ETRS89-extended / LAEA Europe	Lambert Azimuthal Equal Area
4	Italy - onshore and offshore - east of 12°E in...	EPSG	3065	False	IGM95 / UTM zone 33N	Transverse Mercator
...	...	...	...	...	...	...
20	Italy - onshore and offshore.	EPSG	7794	False	RDN2008 / Italy zone (E-N)	Transverse Mercator
21	Italy - onshore and offshore.	EPSG	7795	False	RDN2008 / Zone 12 (E-N)	Transverse Mercator
22	World.	EPSG	8857	False	WGS 84 / Equal Earth Greenwich	Equal Earth
23	World centred on the Americas.	EPSG	8858	False	WGS 84 / Equal Earth Americas	Equal Earth
24	World centred on Asia-Pacific.	EPSG	8859	False	WGS 84 / Equal Earth Asia-Pacific	Equal Earth

You can then pick one for your future needs:

from cartes.crs import EPSG_3034
EPSG_3034()

<abc.EPSG_3034 object at 0x7fbc5618b770>

Adjusting bounds for a projection

Some definitions in the library set very narrow bounds which are then incompatible with plotting in a larger area. It is possible to set different bounds by subclassing the projection.

from cartes import crs
crs.EPSG_6674()

<abc.EPSG_6674 object at 0x7fbc4d455680>

class Custom(crs.EPSG_6674):
    bbox = {
        "east_longitude": 151,
        "north_latitude": 47,
        "south_latitude": 25,
        "west_longitude": 124,
    }

Custom()

<__main__.Custom object at 0x7fbc4d348090>

Tip