Introduction

This library was created from the coordinates package of
JSky version 3.0. The primary goal is
to create a JavaScript coordinate conversion library for use in a
browser. Secondary goals are to make the library available for Java
applications and node.js applications. It is implemented in Java and is
converted to JavaScript using JSweet.

Installation

coordtxl can be installed using npm:

bash$ npm install coordtxl

Usage

The world coordinate system is specified using a
FITS header stored in a
keyword/value map object. This is an example of such a map based on
a test image from CASA:

{ "ALTRPIX": 1.0, "ALTRVAL": 1474985003.2841744, "BITPIX": -32, "BSCALE": 1.0,
"BTYPE": "Intensity", "BUNIT": " ", "BZERO": 0.0,
"CDELT": [-0.0033333333333333335, 0.0033333333333333335, 1.0, -121128418.21747687],
"CHNCHNKS": 1, "COMMENT": "casacore non-standard usage: 4 LSD, 5 GEO, 6 SOU, 7 GAL",
"CRPIX": [257.0, 257.0, 1.0, 1.0], "CRVAL": [299.86875000000003, 40.73375000000001, 1.0, -0.0],
"CTYPE": ["RA---SIN", "DEC--SIN", "STOKES ", "VOPT "], "CUNIT1": "deg ",
"CUNIT2": "deg ", "CUNIT3": " ", "CUNIT4": "m/s ", "DATE": "2023-06-27T16:23:16.059171",
"DATE-OBS": "2008-11-23T18:58:00.275202", "DISTANCE": 0.0, "END": "", "EQUINOX": 2000.0,
"EXTEND": true, "IMAGENME": "/tmp/iclean-demo/test.residual", "INSTRUME": "VLA ",
"LATPOLE": 40.73375000000001, "LONPOLE": 180.0, "MEMAVAIL": 12.914434432983398,
"MEMREQ": 0.01373291015625, "MPIPROCS": 1, "NAXIS": [4, 512, 512, 1, 1], "OBJECT": "fake ",
"OBSDEC": 40.73375000000001, "OBSERVER": "CASA simulator", "OBSGEO-X": -1601185.3650000019,
"OBSGEO-Y": -5041977.546999999, "OBSGEO-Z": 3554875.8700000006, "OBSRA": 299.86875, "ORIGIN":
"casacore-@PROJECT_VERSION@", "PC1_1": 1.0, "PC1_2": 0.0, "PC1_3": 0.0, "PC1_4": 0.0, "PC2_1": 0.0,
"PC2_2": 1.0, "PC2_3": 0.0, "PC2_4": 0.0, "PC3_1": 0.0, "PC3_2": 0.0, "PC3_3": 1.0, "PC3_4": 0.0,
"PC4_1": 0.0, "PC4_2": 0.0, "PC4_3": 0.0, "PC4_4": 1.0, "PV2_1": 0.0, "PV2_2": 0.0,
"RADESYS": "FK5 ", "RESTFRQ": 1474985003.2841744, "SIMPLE": true, "SPECSYS": "LSRK ",
"TELESCOP": "VLA ", "TIMESYS": "UTC ", "VELREF": 1 }

represented in JSON format
(referenced as './test-residual-header.json' below). The FITS map
object is used to initialize MapKeywordProvider which provides the
values to the WCSTransform object. This object provides functions for
conversion from image to world coordinates. This is an example of its
usage:

import { Point2D,
WorldCoords,
WCSTransform,
MapKeywordProvider } from 'coordtxl'

import * as fs from 'fs'

// load FITS header
let rawdata = fs.readFileSync('./test-residual-header.json')
let hdr = JSON.parse(rawdata.toString( ))
// create coordtxl map coupler
let kwp = new MapKeywordProvider(hdr)
// create coordinate tranformation object
let wcs = new WCSTransform(kwp)
// check object state
console.log( wcs.isWCS( ) )
// create a point to be transformed
let p = new Point2D(0.0,0.0)
console.log(p)
// convert point from image to world coordinates
wcs.imageToWorldCoords(p,false)
console.log(p)
// create string representation of the point
let wcstr = new WorldCoords(p.getX(),p.getY()).toString( )
console.log( wcstr )
// create X and Y string representation
console.log( new WorldCoords(p.getX(),p.getY()).format(2000) );

FITS Keywords Used

This is a list of the FITS header keywords used from a
WCSKeywordProvider (circa July, 2023) by the WCSTransform
conversion class. Each line includes the member function called, the
keyword retrieved and along with sample values from a test
test.residual interactive clean residual image. The
return values indicates the value actually returned and the fact that
the default value was returned instead of a value supplied from the CASA
FITS header.

1. getDoubleValue: NAXIS1, 4.0
2. getDoubleValue: NAXIS2, 512.0
3. getDoubleValue: EQUINOX, 2000.0
4. findKey: PLTRAH
5. getStringValue: CTYPE1, RA\-\--SIN
6. getStringValue: CTYPE2, DEC\--SIN
7. getDoubleValue: CRPIX1, 257.0
8. getDoubleValue: CRPIX2, 257.0
9. getDoubleValue: CRVAL1, 299.86875000000003
10. getDoubleValue: CRVAL2, 40.73375000000001
11. getDoubleValue: CDELT1, -0.0033333333333333335
12. getDoubleValue: CDELT2, 0.0033333333333333335
13. getDoubleValue: CROTA1, \
14. getDoubleValue: CROTA2, \
15. getDoubleValue: CCPIX1, \
16. getDoubleValue: CCPIX2, \
17. getDoubleValue: CCROT1, \
18. findKey: EQUINOX
19. getDoubleValue: EQUINOX, 2000.0
20. getDoubleValue: DATE-OBS, \
21. getDoubleValue: EPOCH, \
22. findKey: RADECSYS