EarthLocation

class astropy.coordinates.EarthLocation(*args, **kwargs)

Bases: Quantity

Location on the Earth.

Initialization is first attempted assuming geocentric (x, y, z) coordinates are given; if that fails, another attempt is made assuming geodetic coordinates (longitude, latitude, height above a reference ellipsoid). When using the geodetic forms, Longitudes are measured increasing to the east, so west longitudes are negative. Internally, the coordinates are stored as geocentric.

To ensure a specific type of coordinates is used, use the corresponding class methods (from_geocentric and from_geodetic) or initialize the arguments with names (x, y, z for geocentric; lon, lat, height for geodetic). See the class methods for details.

Notes

This class fits into the coordinates transformation framework in that it encodes a position on the ITRS frame. To get a proper ITRS object from this object, use the itrs property.

Attributes Summary

ellipsoid	The default ellipsoid used to convert to geodetic coordinates.
geocentric	Convert to a tuple with X, Y, and Z as quantities.
geodetic	Convert to geodetic coordinates for the default ellipsoid.
height	Height of the location, for the default ellipsoid.
info	Container for meta information like name, description, format.
itrs	An ITRS object for the location of this object at the default obstime.
lat	Latitude of the location, for the default ellipsoid.
lon	Longitude of the location, for the default ellipsoid.
x	The X component of the geocentric coordinates.
y	The Y component of the geocentric coordinates.
z	The Z component of the geocentric coordinates.

Methods Summary

from_geocentric(x, y, z[, unit])	Location on Earth, initialized from geocentric coordinates.
from_geodetic(lon, lat[, height, ellipsoid])	Location on Earth, initialized from geodetic coordinates.
get_gcrs(obstime)	GCRS position with velocity at obstime as a GCRS coordinate.
get_gcrs_posvel(obstime)	Calculate the GCRS position and velocity of this object at the requested obstime.
get_itrs([obstime, location])	Generates an ITRS object with the location of this object at the requested obstime, either geocentric, or topocentric relative to a given location.
get_site_names(*[, refresh_cache])	Get list of names of observatories for use with of_site.
gravitational_redshift(obstime[, bodies, masses])	Return the gravitational redshift at this EarthLocation.
of_address(address[, get_height, google_api_key])	Return an object of this class for a given address by querying either the OpenStreetMap Nominatim tool [1] (default) or the Google geocoding API [2], which requires a specified API key.
of_site(site_name, *[, refresh_cache])	Return an object of this class for a known observatory/site by name.
to_geocentric()	Convert to a tuple with X, Y, and Z as quantities.
to_geodetic([ellipsoid])	Convert to geodetic coordinates.

Attributes Documentation

ellipsoid

The default ellipsoid used to convert to geodetic coordinates.

geocentric

Convert to a tuple with X, Y, and Z as quantities.

geodetic

Convert to geodetic coordinates for the default ellipsoid.

height

Height of the location, for the default ellipsoid.

info

Container for meta information like name, description, format. This is required when the object is used as a mixin column within a table, but can be used as a general way to store meta information.

itrs

An ITRS object for the location of this object at the default obstime.

lat

Latitude of the location, for the default ellipsoid.

lon

Longitude of the location, for the default ellipsoid.

x

The X component of the geocentric coordinates.

y

The Y component of the geocentric coordinates.

z

The Z component of the geocentric coordinates.

Methods Documentation

classmethod from_geocentric(x, y, z, unit=None)

Location on Earth, initialized from geocentric coordinates.

Parameters:

x, y, zQuantity or array_like

Cartesian coordinates. If not quantities, unit should be given.

unitastropy:unit-like or None

Physical unit of the coordinate values. If x, y, and/or z are quantities, they will be converted to this unit.

Raises:

astropy.units.UnitsError

If the units on x, y, and z do not match or an invalid unit is given.

ValueError

If the shapes of x, y, and z do not match.

TypeError

If x is not a Quantity and no unit is given.

classmethod from_geodetic(lon, lat, height=0.0, ellipsoid=None)

Location on Earth, initialized from geodetic coordinates.

Parameters:

lonLongitude or float

Earth East longitude. Can be anything that initialises an Angle object (if float, in degrees).

latLatitude or float

Earth latitude. Can be anything that initialises an Latitude object (if float, in degrees).

heightQuantity [:ref: ‘length’] or float, optional

Height above reference ellipsoid (if float, in meters; default: 0).

ellipsoidstr, optional

Name of the reference ellipsoid to use (default: ‘WGS84’). Available ellipsoids are: ‘WGS84’, ‘GRS80’, ‘WGS72’.

Raises:

astropy.units.UnitsError

If the units on lon and lat are inconsistent with angular ones, or that on height with a length.

ValueError

If lon, lat, and height do not have the same shape, or if ellipsoid is not recognized as among the ones implemented.

Notes

For the conversion to geocentric coordinates, the ERFA routine gd2gc is used. See liberfa/erfa

get_gcrs(obstime)

GCRS position with velocity at obstime as a GCRS coordinate.

Parameters:

obstimeTime

The obstime to calculate the GCRS position/velocity at.

Returns:

gcrsGCRS instance

With velocity included.

get_gcrs_posvel(obstime)

Calculate the GCRS position and velocity of this object at the requested obstime.

Parameters:

obstimeTime

The obstime to calculate the GCRS position/velocity at.

Returns:

obsgeolocCartesianRepresentation

The GCRS position of the object

obsgeovelCartesianRepresentation

The GCRS velocity of the object

get_itrs(obstime=None, location=None)

Generates an ITRS object with the location of this object at the requested obstime, either geocentric, or topocentric relative to a given location.

Parameters:

obstimeTime or None

The obstime to apply to the new ITRS, or if None, the default obstime will be used.

locationEarthLocation or None

A possible observer’s location, for a topocentric ITRS position. If not given (default), a geocentric ITRS object will be created.

Returns:

itrsITRS

The new object in the ITRS frame, either geocentric or topocentric relative to the given location.

classmethod get_site_names(*, refresh_cache=False)

Get list of names of observatories for use with of_site.

Note

This function is meant to access the site registry from the astropy data server, which is saved in the user’s local cache. If you would like a site to be added there, issue a pull request to the astropy-data repository . If the cache already exists the function will use it even if the version in the astropy-data repository has been updated unless the refresh_cache=True option is used. If there is no cache and the online version cannot be reached, this function falls back on a built-in list, which currently only contains the Greenwich Royal Observatory as an example case.

Parameters:

refresh_cachebool, optional

If True, force replacement of the cached registry with a newly downloaded version. (Default: False)

New in version 5.3.

Returns:

nameslist of str

List of valid observatory names

See also

of_site

Gets the actual location object for one of the sites names this returns.

gravitational_redshift(obstime, bodies=['sun', 'jupiter', 'moon'], masses={})

Return the gravitational redshift at this EarthLocation.

Calculates the gravitational redshift, of order 3 m/s, due to the requested solar system bodies.

Parameters:

obstimeTime

The obstime to calculate the redshift at.

bodiesiterable, optional

The bodies (other than the Earth) to include in the redshift calculation. List elements should be any body name get_body_barycentric accepts. Defaults to Jupiter, the Sun, and the Moon. Earth is always included (because the class represents an Earth location).

massesdict[str, Quantity], optional

The mass or gravitational parameters (G * mass) to assume for the bodies requested in bodies. Can be used to override the defaults for the Sun, Jupiter, the Moon, and the Earth, or to pass in masses for other bodies.

Returns:

redshiftQuantity

Gravitational redshift in velocity units at given obstime.

classmethod of_address(address, get_height=False, google_api_key=None)

Return an object of this class for a given address by querying either the OpenStreetMap Nominatim tool [1] (default) or the Google geocoding API [2], which requires a specified API key.

This is intended as a quick convenience function to get easy access to locations. If you need to specify a precise location, you should use the initializer directly and pass in a longitude, latitude, and elevation.

In the background, this just issues a web query to either of the APIs noted above. This is not meant to be abused! Both OpenStreetMap and Google use IP-based query limiting and will ban your IP if you send more than a few thousand queries per hour [2].

Warning

If the query returns more than one location (e.g., searching on address='springfield'), this function will use the first returned location.

Parameters:

addressstr

The address to get the location for. As per the Google maps API, this can be a fully specified street address (e.g., 123 Main St., New York, NY) or a city name (e.g., Danbury, CT), or etc.

get_heightbool, optional

This only works when using the Google API! See the google_api_key block below. Use the retrieved location to perform a second query to the Google maps elevation API to retrieve the height of the input address [3].

google_api_keystr, optional

A Google API key with the Geocoding API and (optionally) the elevation API enabled. See [4] for more information.

Returns:

locationEarthLocation (or subclass) instance

The location of the input address. Will be type(this class)

References

[1] (1,2)

https://nominatim.openstreetmap.org/

[2] (1,2,3)

https://developers.google.com/maps/documentation/geocoding/start

[3]

https://developers.google.com/maps/documentation/elevation/start

[4]

https://developers.google.com/maps/documentation/geocoding/get-api-key

classmethod of_site(site_name, *, refresh_cache=False)

Return an object of this class for a known observatory/site by name.

This is intended as a quick convenience function to get basic site information, not a fully-featured exhaustive registry of observatories and all their properties.

Additional information about the site is stored in the .info.meta dictionary of sites obtained using this method (see the examples below).

Note

This function is meant to access the site registry from the astropy data server, which is saved in the user’s local cache. If you would like a site to be added there, issue a pull request to the astropy-data repository . If the cache already exists the function will use it even if the version in the astropy-data repository has been updated unless the refresh_cache=True option is used. If there is no cache and the online version cannot be reached, this function falls back on a built-in list, which currently only contains the Greenwich Royal Observatory as an example case.

Parameters:

site_namestr

Name of the observatory (case-insensitive).

refresh_cachebool, optional

If True, force replacement of the cached registry with a newly downloaded version. (Default: False)

New in version 5.3.

Returns:

siteEarthLocation (or subclass) instance

The location of the observatory. The returned class will be the same as this class.

See also

get_site_names

the list of sites that this function can access

Examples

>>> from astropy.coordinates import EarthLocation
>>> keck = EarthLocation.of_site('Keck Observatory')  
>>> keck.geodetic  
GeodeticLocation(lon=<Longitude -155.47833333 deg>, lat=<Latitude 19.82833333 deg>, height=<Quantity 4160. m>)
>>> keck.info  
name = W. M. Keck Observatory
dtype = (float64, float64, float64)
unit = m
class = EarthLocation
n_bad = 0
>>> keck.info.meta  
{'source': 'IRAF Observatory Database', 'timezone': 'US/Hawaii'}

to_geocentric()

Convert to a tuple with X, Y, and Z as quantities.

to_geodetic(ellipsoid=None)

Convert to geodetic coordinates.

Parameters:

ellipsoidstr, optional

Reference ellipsoid to use. Default is the one the coordinates were initialized with. Available are: ‘WGS84’, ‘GRS80’, ‘WGS72’

Returns:

lon, lat, heightQuantity

The tuple is a GeodeticLocation namedtuple and is comprised of instances of Longitude, Latitude, and Quantity.

Raises:

ValueError

if ellipsoid is not recognized as among the ones implemented.

Notes

For the conversion to geodetic coordinates, the ERFA routine gc2gd is used. See liberfa/erfa