Struct Wcs 

pub struct Wcs { /* private fields */ }

The world coordinate system of an image.

Built from a header’s CRPIXn, CRVALn, CDELTn, CDi_j, CROTAn and CTYPEn cards, this converts between pixel positions and the sky coordinates they fall on. The first two axes carry the projection, and Wcs::pixel_to_world works on those; a cube’s remaining axes are read one at a time through Wcs::pixel_to_world_axis.

Pixel coordinates follow the FITS convention: the centre of the first pixel is (1.0, 1.0), not (0.0, 0.0). Use Wcs::pixel_to_world_indexed and Wcs::world_to_pixel_indexed to work in zero-based array indices instead.

A pixel the projection cannot place on the sky — a corner of an all-sky image falls outside the sky itself — comes back as NaN rather than as a plausible coordinate somewhere else.

Implementations

impl Wcs

pub fn from_header( header: &Header, ) -> Result<Self, Box<dyn Error + Send + Sync>>

Reads the world coordinate system out of header.

Errors

Returns an error when the header carries no usable WCS — CRPIXn and CRVALn are both required — when it names a projection this crate does not implement, or when its celestial axes are given in units other than degrees.

pub fn transform(&self) -> [[f64; 2]; 2]

The matrix taking pixel offsets to intermediate world coordinates, row-major.

Whichever of the three conventions the header used — a CDi_j matrix, a PCi_j matrix with CDELTn, or CDELTn with CROTAn — this is what it came to.

pub fn projection(&self) -> Projection

The projection this system uses.

pub fn is_celestial(&self) -> bool

Whether the first two axes describe a position on the sky, as opposed to a plain linear pair.

pub fn celestial_pole(&self) -> Option<(f64, f64)>

The celestial coordinates of the projection’s own pole, in degrees, for a system that has one.

For the zenithal projections — TAN among them — this is the reference point itself. For the whole-sky projections it is a quarter turn away from it, which is what an all-sky map is drawn about.

pub fn axis_count(&self) -> usize

How many axes the header describes.

pub fn axis_type(&self, axis: usize) -> Option<&str>

The CTYPEn of an axis, counting from zero.

pub fn axis_unit(&self, axis: usize) -> Option<&str>

The CUNITn of an axis, counting from zero — the unit its world coordinates are in.

pub fn pixel_to_world_axis(&self, axis: usize, pixel: f64) -> Option<f64>

The world coordinate at a pixel along one axis, counting from zero.

This is how a cube’s third axis is read: the wavelength, frequency or time a plane was taken at. pixel is one-based, as FITS counts pixels.

A -LOG axis is read as the standard defines it, with the coordinate growing geometrically rather than by a fixed step. The two celestial axes have no coordinate of their own — they only mean anything together — so they come back None; Wcs::pixel_to_world is what reads those.

pub fn world_to_pixel_axis(&self, axis: usize, world: f64) -> Option<f64>

The pixel a world coordinate falls on along one axis, the inverse of Wcs::pixel_to_world_axis.

pub fn pixel_to_world(&self, pixel: (f64, f64)) -> (f64, f64)

The sky coordinate at a pixel, in degrees.

pixel is one-based, as FITS counts pixels.

pub fn world_to_pixel(&self, world: (f64, f64)) -> (f64, f64)

The pixel a sky coordinate falls on, in degrees in and one-based pixels out.

pub fn pixel_to_world_indexed(&self, index: (u32, u32)) -> (f64, f64)

As Wcs::pixel_to_world, but taking a zero-based array index.

pub fn world_to_pixel_indexed( &self, world: (f64, f64), width: u32, height: u32, ) -> Option<(u32, u32)>

As Wcs::world_to_pixel, but returning a zero-based array index.

The index is rounded to the nearest pixel, and None when the coordinate falls outside the width by height image.

Trait Implementations

impl Clone for Wcs

fn clone(&self) -> Wcs

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Wcs

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl PartialEq for Wcs

fn eq(&self, other: &Wcs) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for Wcs