# Pix2Sky_SlantOrthographic¶

class astropy.modeling.projections.Pix2Sky_SlantOrthographic(xi=0.0, eta=0.0, **kwargs)[source]

Slant orthographic projection - pixel to sky.

Corresponds to the SIN projection in FITS WCS.

See Zenithal for a definition of the full transformation.

The following transformation applies when $$\xi$$ and $$\eta$$ are both zero.

$\theta = \cos^{-1}\left(\frac{\pi}{180^{\circ}}R_\theta\right)$

The parameters $$\xi$$ and $$\eta$$ are defined from the reference point $$(\phi_c, \theta_c)$$ as:

$\begin{split}\xi &= \cot \theta_c \sin \phi_c \\ \eta &= - \cot \theta_c \cos \phi_c\end{split}$
Parameters
xifloat

Obliqueness parameter, ξ. Default is 0.0.

etafloat

Obliqueness parameter, η. Default is 0.0.

Attributes Summary

 eta param_names Names of the parameters that describe models of this type. xi

Methods Summary

 evaluate(x, y, xi, eta) Evaluate the model on some input variables.

Attributes Documentation

eta = Parameter('eta', value=0.0)
param_names = ('xi', 'eta')

Names of the parameters that describe models of this type.

The parameters in this tuple are in the same order they should be passed in when initializing a model of a specific type. Some types of models, such as polynomial models, have a different number of parameters depending on some other property of the model, such as the degree.

When defining a custom model class the value of this attribute is automatically set by the Parameter attributes defined in the class body.

xi = Parameter('xi', value=0.0)

Methods Documentation

classmethod evaluate(x, y, xi, eta)[source]

Evaluate the model on some input variables.