Crate twirs

source ·
Expand description

Rust port of the astrometric plate solving package twirl.
Currently, no source detection or catalog query is included. This only calculates the transformation between a set of detected sources and a provided catalog. To that end, asterisms of three or four stars are built, hashed, and then matched.
Since it is faithful to the original, most documentation on the chosen algorithm applies.

Interface

The central struct of this library is Twirs. It is used to choose the asterism scheme, specify the sets of points and matching parameters, and find the plate solutions.
In most cases, it should be created with Twirs::triangles() or Twirs::quads(), but for generic contexts, the asterism can be specified in Twirs::new(). In any case, additional parameters are set via Twirs::with_*() functions.

Example:

Twirs::quads(pixels, radecs)
    .with_tolerance(0.5)
    .with_hash_tolerance(1.5);

After constructing the struct, there are two options:

  • Directly calculate the least squares matrix between the 1-padded matrix of pixel and sky coordinates.
  • Calculate the Wcs transformation.

Both can also be executed in parallel.

Parameters

  • hash_tolerance: Maximum allowed Euclidean distance between hashes. This is used in the nearest-neighbor search for matches between pixel and sky coordinates.
  • tolerance: Maximum allowed Euclidean distance between points after applying the transformation. This is used in counting the number of matches to check which transformation is the best.
  • min_match: Minimum number of matches between the pixel and sky coordinates after applying the transformation. If this number of matches is reached, the search for transformations is stopped. A lower number might lead to faster runtimes, but might also terminate the program before finding the optimal transformation.
    Warning: If using parallel execution (e.g. Twirs::find_transform_par()), this option is ignored.

Only when using triangle asterisms:

  • min_angle: Minimum angle of triangle asterisms. Triangles not fulfilling this condition are excluded from the transformation search.

Modules

  • wcs
    Simple implementation of the World Coordinate System standard.

Structs

  • QuadAsterism
    Calculate the hashes using asterisms of four stars.
  • TriangleAsterism
    Calculate the hashes using asterisms of three stars.
  • Twirs
    The central struct of this library.

Traits

  • Asterism
    Generalizes over possible asterisms.
  • Float
    A generic float trait such that the plate solving algorithm is generic over f32/f64.