%YAML 1.1
---
$schema: "http://stsci.edu/schemas/yaml-schema/draft-01"
id: "http://stsci.edu/schemas/asdf/transform/slant_orthographic-1.3.0"
title: |
  The slant orthographic projection.

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

  See
  [zenithal](ref:schemas/zenithal-1.2.0)
  for the definition of the full transformation.

  The pixel-to-sky transformation is defined as:

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

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

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

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

allOf:
  - $ref: "zenithal-1.3.0"
  - type: object
    properties:
      xi:
        anyOf:
          - $ref: "../unit/quantity-1.2.0"
          - type: number
        description: Obliqueness parameter, first equation of the slant
                     orthographic projection.
        default: 0

      eta:
        anyOf:
          - $ref: "../unit/quantity-1.2.0"
          - type: number
        description: Obliqueness parameter, second equation of the slant
                     orthographic projection.
        default: 0
...
