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TWEAKUTILS: Utility Functions for Tweakreg

The functions in this module support the various aspects of tweakreg, including finding the objects in the images and plotting the residuals.

drizzlepac.tweakutils.build_pos_grid(start, end, nstep, mesh=False)

Return a grid of positions starting at X,Y given by ‘start’, and ending at X,Y given by ‘end’. The grid will be completely filled in X and Y by every ‘step’ interval.

drizzlepac.tweakutils.build_xy_zeropoint(imgxy, refxy, searchrad=3.0, histplot=False, figure_id=1)

Create a matrix which contains the delta between each XY position and each UV position.


Generate a WCS header object that can be used to populate a reference WCS HDU.

For most applications, stwcs.wcsutil.HSTWCS.wcs2header() will work just as well.

drizzlepac.tweakutils.find_xy_peak(img, center=None)

Find the center of the peak of offsets

drizzlepac.tweakutils.gauss(x, sigma)

Compute 1-D value of gaussian at position x relative to center.

drizzlepac.tweakutils.gauss_array(nx, ny=None, fwhm=1.0, sigma_x=None, sigma_y=None, zero_norm=False)

Computes the 2D Gaussian with size nx*ny.

Parameters :

nx : int

ny : int [Default: None]

Size of output array for the generated Gaussian. If ny == None, output will be an array nx X nx pixels.

fwhm : float [Default: 1.0]

Full-width, half-maximum of the Gaussian to be generated

sigma_x : float [Default: None]

sigma_y : float [Default: None]

Sigma_x and sigma_y are the stddev of the Gaussian functions.

zero_norm : bool [Default: False]

The kernel will be normalized to a sum of 1 when True.

Returns :

gauss_arr : array

A numpy array with the generated gaussian function


Return True if all characters are part of a floating point value

drizzlepac.tweakutils.make_vector_plot(coordfile, columns=[1, 2, 3, 4], data=None, figure_id=None, title=None, axes=None, every=1, limit=None, xlower=None, ylower=None, output=None, headl=4, headw=3, xsh=0.0, ysh=0.0, fit=None, scale=1.0, vector=True, textscale=5, append=False, linfit=False, rms=True)

Convert a XYXYMATCH file into a vector plot or set of residuals plots.

This function provides a single interface for generating either a vector plot of residuals or a set of 4 plots showing residuals. The data being plotted can also be adjusted for a linear fit on-the-fly.

Parameters :

coordfile : string

Name of file with matched sets of coordinates. This input file can be a file compatible for use with IRAF’s geomap.

columns : list [Default: [0,1,2,3]]

Column numbers for the X,Y positions from each image

data : list of arrays

If specified, this can be used to input matched data directly

title : string

Title to be used for the generated plot

axes : list

List of X and Y min/max values to customize the plot axes

every : int [Default: 1]

Slice value for the data to be plotted

limit : float

Radial offset limit for selecting which sources are included in the plot

xlower : float

ylower : float

Limit in X and/or Y offset for selecting which sources are included in the plot

output : string

Filename of output file for generated plot

headl : int [Default: 4]

Length of arrow head to be used in vector plot

headw : int [Default: 3]

Width of arrow head to be used in vector plot

xsh : float

ysh : float

Shift in X and Y from linear fit to be applied to source positions from the first image

scale : float

Scale from linear fit to be applied to source positions from the first image

fit : array

Array of linear coefficients for rotation (and scale?) in X and Y from a linear fit to be applied to source positions from the first image

vector : bool [Default: True]

Specifies whether or not to generate a vector plot. If False, task will generate a set of 4 residuals plots instead

textscale : int [Default: 5]

Scale factor for text used for labelling the generated plot

append : bool [Default: False]

If True, will overplot new plot on any pre-existing plot

linfit : bool [Default: False]

If True, a linear fit to the residuals will be generated and added to the generated residuals plots

rms : bool [Default: True]

Specifies whether or not to report the RMS of the residuals as a label on the generated plot(s).

drizzlepac.tweakutils.ndfind_old(array, hmin, fwhm, sharplim=[0.2, 1.0], roundlim=[-1, 1], minpix=5, datamax=None)

Source finding algorithm based on NDIMAGE routines

This function provides a simple replacement for the DAOFIND task.

Parameters :

array : arr

Input image as numpy array

hmin : float

Limit for source detection in pixel values

fwhm : float

Full-width half-maximum of the PSF in the image

minpix : int

Minimum number of pixels for any valid source

sharplim : tuple

[Not used at this time]

roundlim : tuple

[Not used at this time]

datamax : float

Maximum good pixel value found in any detected source

Returns :

x : arr

Array of detected source X positions (in array coordinates, 0-based)

y : arr

Array of detected source Y positions (in array coordinates, 0-based)

flux : arr

Array of detected source fluxes in pixel values

id : arr

Array of detected source ID numbers


Return the list of catalog filenames specified as part of the input @-file


Common function to interpret input column names provided by the user.

This function translates column specification provided by the user into a column number.

Parameters :

colname : :

Column name or names to be interpreted

Returns :

cols : list

The return value will be a list of strings.


This function will understand the following inputs:

'1,2,3' or   'c1,c2,c3' or ['c1','c2','c3']
'1-3'   or   'c1-c3'
'1:3'   or   'c1:c3'
'1 2 3' or   'c1 c2 c3'
'1'     or   'c1'

Read in exclusion definitions from file named by ‘exclusions’ and return a list of positions and distances

drizzlepac.tweakutils.parse_skypos(ra, dec)

Function to parse RA and Dec input values and turn them into decimal degrees

Input formats could be:
[“nn”,”nn”,”nn.nn”] “nn nn nn.nnn” “nn:nn:nn.nn” “nnH nnM nn.nnS” or “nnD nnM nn.nnS” nn.nnnnnnnn “nn.nnnnnnn”

Plot 2d histogram.

Pars will be a dictionary containing:
data, figure_id, vmax, title_str, xp,yp, searchrad
drizzlepac.tweakutils.radec_hmstodd(ra, dec)

Function to convert HMS values into decimal degrees.

This function relies on the astrolib.coords package to perform the conversion to decimal degrees.

Parameters :

ra : list or array

List or array of input RA positions

dec : list or array

List or array of input Dec positions

Returns :

pos : arr

Array of RA,Dec positions in decimal degrees

See also



Formats of ra and dec inputs supported:

"nn nn nn.nnn"
"nnH nnM nn.nnS" or "nnD nnM nn.nnS"
drizzlepac.tweakutils.read_ASCII_cols(infile, cols=[1, 2, 3])

Interpret input ASCII file to return arrays for specified columns.

Returns :

outarr : list of arrays

The return value will be a list of numpy arrays, one for each ‘column’.


The specification of the columns should be expected to have lists for each ‘column’, with all columns in each list combined into a single entry. For example:

cols = ['1,2,3','4,5,6',7]

where ‘1,2,3’ represent the X/RA values, ‘4,5,6’ represent the Y/Dec values and 7 represents the flux value for a total of 3 requested columns of data to be returned.

drizzlepac.tweakutils.read_FITS_cols(infile, cols=None)

Read columns from FITS table

drizzlepac.tweakutils.readcols(infile, cols=None)

Function which reads specified columns from either FITS tables or ASCII files

This function reads in the columns specified by the user into numpy arrays regardless of the format of the input table (ASCII or FITS table).

Parameters :

infile : string

Filename of the input file

cols : string or list of strings

Columns to be read into arrays

Returns :

outarr : array

Numpy array or arrays of columns from the table

drizzlepac.tweakutils.write_shiftfile(image_list, filename, outwcs='tweak_wcs.fits')

Write out a shiftfile for a given list of input Image class objects