%YAML 1.1
---
$schema: "http://stsci.edu/schemas/yaml-schema/draft-01"
id: "http://stsci.edu/schemas/asdf/transform/slant_zenithal_perspective-1.1.0"
title: |
  The slant zenithal perspective projection.

description: |
  Corresponds to the `SZP` projection in the FITS WCS standard.

  See
  [zenithal](ref:schemas/zenithal-1.1.0)
  for the definition of the full transformation.

  The pixel-to-sky transformation is defined as:

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

  And the sky-to-pixel transformation is defined as:

  $$R_\theta = \frac{180^{\circ}}{\pi}\cot \theta$$

  Invertibility: All ASDF tools are required to provide the inverse of
  this transform.

allOf:
  - $ref: "zenithal-1.1.0"
  - type: object
    properties:
      mu:
        type: number
        description: |
          Distance from point of projection to center of sphere in
          spherical radii.
        default: 0

      phi0:
        type: number
        description: |
          The longitude $\phi_0$ of the reference point, in degrees.
        default: 0

      theta0:
        type: number
        description: |
          The latitude $\theta_0$ of the reference point, in degrees.
        default: 90
...
