dysh for GBTIDL Users

Some key differences

• No longer tied to a single input and output file, can load as many SDFITS files as RAM allows

• No longer tied to a finite number of data containers, you can have as many ScanBlock/Spectrum objects as RAM allows

• Python allows for well-trackable local and global variables

Rough equivalents

In the tables below, it is assumed you have executed the following commands in Python:

from dysh.fits.gbtfitsload import GBTFITSLoad

File I/O and Metadata Operations

GBTIDL	dysh	Notes
online	sdf = GBTOnline(); sdf = GBTOnline([projID])	Monitor the currently online project or a specific project projID. Load the SDFITS into sdf.
offline	sdf = GBTOffline([projID])	Load data from project/session projID into sdf.
filein, [SDFITS file]	sdfits = GBTFITSLoad( [SDFITSfile] )	This will directly load a SDFITS file into python.
dirin, [SDFITS dir]	sdfits = GBTFITSLoad( [SDFITS dir] )	This will load each SDFITS file in a directory into python, in the case it is a project directory where each file is a different VEGAS bank. (A, B, C, etc.). The implementation is identical to the single SDFITS file load.
fileout		There is no direct translation; in dysh, simply specify a filename with the spectrum.write function
keep	spec.write( [SDFITSfile], format=[fmt] )	Write the spectrum spec to the output SDFITS file specified, using the format fmt
summary	sdfits.summary()	In dysh, you can also input a list of scan numbers you would like to see.
list	sdfits.summary( verbose=True )	Using the “verbose=True” option returns similar results to GBTIDL’s “list”.
header, scan_info	spec.meta	Return meta information about the spectrum spec. In GBTIDL, this returns a text printout. In dysh, this returns a dictionary with all SDFITS keywords and values.

Calibration and Data Retrieval

GBTIDL	dysh	explanation
select	sdf.select( [col1]=[val1], [col2]=[val2] )	Select subsets of the GBTFITSLoad object sdf based on the constraints on col1 and col2 given by val1 and val2
flag	sdf.flag( [col1]=[val1], [col2]=[val2] )	Create flagging rules of the GBTFITSLoad object sdf based on the constraints on col1 and col2 given by val1 and val2. See flagging examples given in the Recipes.
gettp, [scan_num]	sdfits.gettp( scan=[scan_num] )	Returns a Scan Block. Get a total power scan, with the option in dysh to optionally calibrate it.
getps, [scan_num]	sdfits.getps( scan=[scan_num] )	Returns a Scan Block. Retrieve and calibrate position-switched data.
getfs, [scan_num]	sdfits.getfs( scan=[scan_num] )	Returns a Scan Block. Retrieve and calibrate frequency-switched data.
getnod, [scan_num]	sdfits.getnod( scan=[scan_num] )	Returns a Scan Block.
show	spec.plot()	Plot the spectrum spec. Calibration routines in GBTIDL do this automatically.

Spectrum Operations

GBTIDL	dysh	Notes
baseline, bshape, bsubtract, nfit	spec.baseline( [deg], exclude=[ex_reg],remove=True/False )	Compute and optionally remove a baseline with degree deg and exclusion regions ex_reg
gsmooth, [int]	spec.smooth( “gauss”, [int] )	Convolve spec with a Gaussian kernel. Default behavior is to decimate, which isn’t true in GBTIDL
hanning	spec.smooth( “hann” )	Convolve spec with a Hanning window. Default behavior is to decimate, which isn’t true in GBTIDL
boxcar, [int]	spec.smooth( “box”, [int] )	Convolve spec with a boxcar window. This matches the GBTIDL results only when integer int is an odd number. Default behavior is to decimate, which isn’t true in GBTIDL
add/subtract/divide/scale	spec + other, spec - other, spec/other, spec*other	Perform element-wise math between spectrum spec and other vector/scalar other.
bias, [bias]	spec + bias	Add scalar bias to spectrum spec. The units of bias must match those of spec.flux.
accum	average_spectra(list of spectra)
ave	scanblock.timeaverage(); scan.timeaverage()	Average a set of scans inside Scan Block scanblock or Scan scan.
stats	spec.stats()	Print statistics of spectrum spec.
fshift, vshift, xshift	spec.find_shift(other)	Find the shift between spec and other.
gshift	spec.shift(shift) spec.align_to(other)	Shift spec by shift. Find the shift between spec and other and apply. Equivalent to spec.shift(spec.find_shift(other)).
write_ascii, filename	spec.write(filename, format=”ascii.basic”)	Write the contents of spec to a text file in ascii format with minimum header information.