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Module Fits.Unit

FITS unit strings (FITS 4.0 §4.3).

A unit string is an optional power of ten (10**k, 10^k, 10+k or 10-k) then products of symbols by a space, * or ., and divisions by /, each dividing by the product that follows it: erg/cm2 s is erg cm^-2 s^-1. A symbol is raised to a power by **, ^ or trailing digits (cm-2), and to a rational one in parentheses (m(3/2), m**(1.5)). Case is significant. Parsing is linear in the string's length.

#val vocabulary : Ymir_units.Vocabulary.t

vocabulary is FITS 4.0 Tables 3 and 4 at the standard's values (a parsec is 3.0857e16 m, a solar mass 1.9891e30 kg), with the prefixes of Table 5 on the symbols the standard allows them, and the archives' spellings Angstrom, angstrom, electron, ELECTRONS, DN and COUNTS. mag, count, photon, bit, adu, bin, Sun, electron and DN are symbols.

val parse : 
  ?scope:string ->
  string ->
  (Ymir_units.Unit.t, string) Stdlib.result

parse ~scope s is the unit s spells. The data-set symbols pix and pixel (one unit), voxel, chan and beam are Ymir_units.Unit.scoped ~scope; without scope they are an Error. log(), ln(), exp() and sqrt() of a dimensioned unit are an Error: they make no monomial.

#val print : Ymir_units.Unit.t -> (string, string) Stdlib.result

print u spells u with vocabulary, as MJy sr-1, scoped symbols last by name; "" for the dimensionless unit. Error if no product of FITS symbols, prefixes and a power of ten is u. Writing a unit is Header.set Value.string "BUNIT" of its text.