CylindricalEqualAreaProjection

class sofia_redux.scan.coordinate_systems.projection.cylindrical_equal_area_projection.CylindricalEqualAreaProjection

Bases: CylindricalProjection

Initialize a cylindrical equal-area projection.

The cylindrical equal-area projection maps spherical coordinates onto a stretched vertical cylinder, with meridians as equally spaced vertical lines, and parallels as horizontal lines. In this model, the stretch parameter is applied to the vertical axis, but is typically set to 1 (Lambert projection).

Methods Summary

edit_header(header[, alt])	Edit a FITS header with the projection information.
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) theta (latitude) coordinates.
parse_header(header[, alt])	Parse and apply a FITS header to the projection.

Methods Documentation

edit_header(header, alt='')

Edit a FITS header with the projection information.

Parameters:

headerfits.Header

The FITS header to edit.

altstr, optional

The alternate FITS system.

Returns:

None

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 cylindrical equal-area projection, this is given as:

x = phi y = stretch * sin(theta)

Parameters:

thetaunits.Quantity

The theta angle.

phiunits.Quantity

The phi angle.

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) 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.

The cylindrical equal-area transform is very simple, of the form:

phi = x theta = arcsin(stretch * y)

Parameters:

offsetCoordinate2D

phi_thetaSphericalCoordinates, optional

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

Returns:

coordinatesSphericalCoordinates

parse_header(header, alt='')

Parse and apply a FITS header to the projection.

Parameters:

headerfits.Header

The FITS header to parse.

altstr, optional

The alternate FITS system.

Returns:

None