Although you can transform an image/cube, the default only needs to know the distance (in AU, pc, kpc, mpc, z, ...) and unit size (in AU, pc, kpc, mpc, ....) of the object. This will give you the scaling factors for length and velocities.
When the distance is given in z, Wright’s (2006) cosmology calculator is used.
WMAP-9 (2011) 71 0.27 0.73 Planck (2013) 67.15 0.317 0.683 Planck (2018) 67.66 0.3111 0.6889
% ccdsky d=1,pc r=1,AU v=1,km/s d=1 pc r=1 AU v=1 km/s rscale=0.000277785 (1.00003 arcsec) vscale=1000
To find out the radius of 2 pc at the distance of the galactic center:
ccdsky r=2,pc d=8.5,kpc rscale=0.0134814 (48.5329 arcsec)
Here is an example of creating a small bar, at position angle 30, and
observed at RA=6h and DEC=30d:
% ccdgen "" map4 bar 1,10,0.5,30 size=512,512,1 % ccdsky map4 map4b % ccdfits in=map4b out=map4b.fits radecvel=t crval=90,30 crpix=256.5,256.5 % # now switch to MIRIAD % fits in=map4b.fits out=map4b.mir op=xyin % cgdisp in=map4b.mir device=/xs labtyp=arcminand you should see a bar (possibly with a sign error position angle) of about 1 arcmin in length, in an 8 arcmin field. Notice that ccdfits(1NEMO) also has various options to specify a WCS which can override the one set by ccdgen(1NEMO) .
Here is a cosmological example:
% ccdsky H=67.7,0.307,0.693 d=2.19,z ------------------------------------------------------------- For H_o = 67.7 Omega_M = 0.31 Omega_vac = 0.69 z = 2.190 It is now 13.830 Gyr since the Big Bang. The age at redshift z was 3.012 Gyr. The light travel time was 10.818 Gyr. The comoving radial distance, which goes into Hubbles law, is 5592.2 Mpc or 18.239 Gly The comoving volume within redshift z is 732.530 Gpc^3. The angular size distance D_A is 1753.026 Mpc or 5.718 Gly. This gives a scale of 8.499 kpc/arcsec The luminosity distance D_L is 17839.0 Mpc or 58.183 Gly. The distance modulus, m-M, is 46.26 ------------------------------------------------------------- d=2.19 z [3635.8 Mpc] r=1 AU v=1 km/s SdV=1 Jy.km/s rscale=1.5846e-13 [ 5.70457e-10 arcsec 5.70457e-07 mas] vscale=1000 iscale=1 Mass(HI) = 7.25098e+11 Mass(H2) = 3.22675e+10 (alpha=4.3; includes 1.36 He contribution)compare this with the (selected) output for gnuastro’s astcosmiccal(1) program:
% astcosmiccal --H0=67.7 --olambda=0.693 --omatter=0.307 -z2.19 CosmicCalculator (GNU Astronomy Utilities) 0.11 Universe now ------------ - Age of Universe now (Ga*): 13.844296 - Critical density now (g/cm^3): 8.610662e-30 - Proper distance to z (Mpc): 5592.995113 - Angular diameter distance to z (Mpc): 1753.290004 - Tangential distance covered by 1 arcsec at z (Kpc): 8.500190 - Luminosity distance to z (Mpc): 17841.654411 - Distance modulus at z (no unit): 46.257176 - Conversion to absolute magnitude (no unit): 44.997699 Universe at desired redshift z ------------------------------ - Age of Universe at z (Ga*): 3.017860 - Look-back time to z (Ga*): 10.826436 - Critical density at z (g/cm^3): 9.177897e-29
http://arxiv.org/abs/astro-ph/0609593 A Cosmology Calculator for the Web (E.Wright)
http://www.astro.ucla.edu/~wright/CosmoCalc.html The CosmoCalc website
https://ui.adsabs.harvard.edu/abs/2013ARA%26A..51..207B/abstract
17-Aug-2012 V1.0 Created PJT 23-aug-2012 V1.1 added sdv= PJT 28-aug-2012 V1.2 implemented scale= PJT 28-feb-2013 V2.2 more verbose, added H= PJT 16-mar-2013 V3.0 added Wright’s cosmology calculator PJT