PolyconicProjection

class sofia_redux.scan.coordinate_systems.projection.polyconic_projection.PolyconicProjection

Bases: SphericalProjection

Initialize a polyconic projection.

The polyconic projection is also known as the American polyconic projection. Each parallel is a circular arc at true scale with a straight equator and the center of each circle lying on the central axis. The longitude of the central meridian lies at zero, with the latitude of the origin at the central meridian also equal to zero.

Notes

Deprojection is not possible for the polyconic projection.

Methods Summary

get_fits_id()	Return the FITS ID for the projection.
get_full_name()	Return the full name of the projection.
get_offsets(theta, phi[, offsets])	Get the offsets given theta and phi.
get_phi_theta(offset[, phi_theta])	Return the phi (longitude) and theta (latitude) coordinates.

Methods Documentation

classmethod get_fits_id()

Return the FITS ID for the projection.

Returns:

str

classmethod get_full_name()

Return the full name of the projection.

Returns:

str

get_offsets(theta, phi, offsets=None)

Get the offsets given theta and phi.

Takes the theta (latitude) and phi (longitude) coordinates about the celestial pole and converts them to offsets from a reference position. For the polyconic projection when theta is non-zero, this is given by:

x = cot(theta) * sin(phi * sin(theta)) y = theta + cot(theta) * (1 - cos(phi * sin(theta)))

If theta is equal to zero, then to avoid zero division:

x = phi y = 0

Parameters:

thetaunits.Quantity or float

The theta (latitude) angle. If a float value is provided, it should be in radians.

phiunits.Quantity or float

The phi (longitude) angle. If a float value is provided, it should be in radians.

offsetsCoordinate2D, optional

An optional coordinate system in which to place the results.

Returns:

offsetsCoordinate2D

get_phi_theta(offset, phi_theta=None)

Return the phi (longitude) and theta (latitude) coordinates.

The phi and theta coordinates refer to the inverse projection (deprojection) of projected offsets about the native pole. phi is the deprojected longitude, and theta is the deprojected latitude of the offsets. This method is not implemented for the polyconic projection.

Parameters:

offsetCoordinate2D

phi_thetaSphericalCoordinates, optional

An optional output coordinate system in which to place the results.

Returns:

coordinatesSphericalCoordinates