Usage for gjincBeam

Return to directory of Todd's CASA extensions

This function attempts to predict the effective restoring beam obtained from the casa command sdimaging when using the GJINC gridding kernel. The Jinc1 function is computed using scipy. A comparison was made between this and the grdjinc1 function in CASA, which is an approximate formula, and they agree to ~8 digits (see this overlay plot). See also sfBeam and getTPSampling. Note that to accurately reflect the current knowledge of the ALMA 12m antenna beam from holography measurements, one should use taper=10 (which will yield 1.131 lambda / D).

Usage:

au.gjincBeam(frequency, pixelsize=10, diameter=12.0, 
                      xSamplesPerBeam=5.0, ySamplesPerBeam=None, 
                      xSamplingArcsec=None, ySamplingArcsec=None,
                      makeplot=False, taper=10.0, geometricMean=False,
                      obscuration=0.75, widthMultiplier=1.0, useCasaJinc=False,
                      testOption=False, minlevels=[0.0], truncate=True, img=None,
                      row=None, column=None, stokes='XX', plotfile='',
                      verbose=False, fwhmfactor=None, excludeBand3=True, excludeBand3Below=109.0)

Inputs:

  • frequency: floating point number in GHz (no units) or a string with units
  • pixelsize: floating point number in arcseconds (no units)
  • diameter: the diameter of the single dish antenna in meters (no units)
  • xSamplesPerBeam: the number of sampled points per telescope FWHM beam along the X axis
  • ySamplesPerBeam: the number of sampled points per telescope FWHM beam along the Y axis
  • xSamplingArcsec: if not None, then use this value instead of xSamplesPerBeam
  • ySamplingArcsec: if not None, then use this value instead of ySamplesPerBeam
  • makeplot: if True, then also generate a plot
  • taper: the illumination taper (in dB) to pass to au.primaryBeamArcsec
  • fwhmfactor: if specified, pass this to au.primaryBeamArcsec, overriding taper
  • obscuration: diameter in m to pass to au.primaryBeamArcsec
  • geometricMean: if True, then return only the geometric mean beamsize; otherwise, return minorAxis,majorAxis,geometricMean (if the sampling is provided in both axes)
  • widthMultiplier: the value by which to multiply the default values of gwidth/jwidth
  • useCasaJinc: if True, then use grdjinc1 which was extracted from CASA (which uses an approximate formula). If False, use scipy (which is more accurate). The results are nearly identical.
  • testOption: not currently used
  • minlevels: a list of fractional values (from 0..1) above which to perform 1D Gaussian fits on the estimated restoring beam
  • truncate: only used if taper=0, sets whether to truncate the Airy at the first null
  • img: if not none, then use a row or column from this image as the beam model
  • row: the row of img to use as the starting beam profile model
  • column: the column of img to use as the starting beam profile model
  • stokes: 'XX','YY' which Stokes to use in the img
  • excludeBand3: if True, then don't use Band 3 TICRA patterns below excludeBand3Below'
  • excludeBand3Below: frequency in GHz below which to not use Band 3 patterns

Returns:

  • If only the X-axis sampling is given:
    • the FWHM of the restoring beam
    • the FWHM of a Gaussian fit to the restoring beam
  • If both X and Y-axis sampling is given: * If geometricMean=True: * the FWHM of the predicted restoring beam * the FWHM of a Gaussian fit to the predicted restoring beam * If geometricMean=False: * the minor axis of the restoring beam * the major axis of the restoring beam * the geometric mean of the restoring beam computed using findFWHM() * the geometric mean of the FWHM of a Gaussian fit to the restoring beam

Examples:

CASA <12>: au.gjincBeam(115.27,pixelsize=3,taper=10)
  Out[6]: (51.287757483793229, 51.286676672022502)

CASA <14>: au.gjincBeam(336.5,pixelsize=3,taper=10,xSamplingArcsec=3.5,ySamplingArcsec=5.7,makeplot=T)
Plot left in gjincBeam.png
  Out[14]: (18.226274978160909, 18.488102385966258, 18.356721872682328, 18.35236509861296)

  • gjincBeam.png:
    gjincBeam.png

  • A comparison of the grdjinc1 function from casa, and scipy's implementation, which is used in this function.
    jinc1 comparison.png
-- ToddHunter - 2013-06-27
Topic attachments
I AttachmentSorted ascending Action Size Date Who Comment
gjincBeam.pngpng gjincBeam.png manage 101 K 2013-11-15 - 14:03 ToddHunter  
jinc1_comparison.pngpng jinc1_comparison.png manage 55 K 2013-11-15 - 14:28 ToddHunter made with au v1.1481
Topic revision: r14 - 2014-03-27, ToddHunter
This site is powered by FoswikiCopyright © by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
Ideas, requests, problems regarding NRAO Public Wiki? Send feedback