Step Arguments¶
The resample
step has the following optional arguments that control
the behavior of the processing and the characteristics of the resampled
image.
--pixfrac
(float, default=1.0)The fraction by which input pixels are “shrunk” before being drizzled onto the output image grid, given as a real number between 0 and 1.
--kernel
(str, default=’square’)The form of the kernel function used to distribute flux onto the output image. Available kernels are
square
,gaussian
,point
,tophat
,turbo
,lanczos2
, andlanczos3
.--pixel_scale_ratio
(float, default=1.0)Ratio of input to output pixel scale. A value of 0.5 means the output image would have 4 pixels sampling each input pixel. Ignored when
pixel_scale
oroutput_wcs
are provided.--pixel_scale
(float, default=None)Absolute pixel scale in
arcsec
. When provided, overridespixel_scale_ratio
. Ignored whenoutput_wcs
is provided.--rotation
(float, default=None)Position angle of output image’s Y-axis relative to North. A value of 0.0 would orient the final output image to be North up. The default of
None
specifies that the images will not be rotated, but will instead be resampled in the default orientation for the camera with the x and y axes of the resampled image corresponding approximately to the detector axes. Ignored whenpixel_scale
oroutput_wcs
are provided.--crpix
(tuple of float, default=None)Position of the reference pixel in the image array in the
x, y
order. Ifcrpix
is not specified, it will be set to the center of the bounding box of the returned WCS object. When supplied from command line, it should be a comma-separated list of floats. Ignored whenoutput_wcs
is provided.--crval
(tuple of float, default=None)Right ascension and declination of the reference pixel. Automatically computed if not provided. When supplied from command line, it should be a comma-separated list of floats. Ignored when
output_wcs
is provided.--output_shape
(tuple of int, default=None)Shape of the image (data array) using “standard”
nx
first andny
second (as opposite to thenumpy.ndarray
convention -ny
first andnx
second). This value will be assigned topixel_shape
andarray_shape
properties of the returned WCS object. When supplied from command line, it should be a comma-separated list of integersnx, ny
.Note
Specifying
output_shape
is required when the WCS inoutput_wcs
does not havebounding_box
property set.--output_wcs
(str, default=’’)File name of a
ASDF
file with a GWCS stored under the"wcs"
key under the root of the file. The output image size is determined from the bounding box of the WCS (if any). Argumentoutput_shape
overrides computed image size and it is required when output WCS does not havebounding_box
property set or ifpixel_shape
orarray_shape
keys (see below) are not provided.Additional information may be stored under other keys under the root of the file. Currently, the following keys are recognized:
pixel_area
: Indicates average pixel area of the output WCS in units of steradians. When provided, this value will be used for updating photometric quantitiesPIXAR_SR
andPIXAR_A2
of the output image. Ifpixel_area
is not provided, the code will attempt to estimate this value from the WCS.pixel_shape
: dimensions of the output image in the order (nx, ny). Overrides the value ofarray_shape
if provided.array_shape
: shape of the output image innumpy
order: (ny, nx).
Note
When
output_wcs
is specified, WCS-related arguments such aspixel_scale_ratio
,pixel_scale
,rotation
,crpix
, andcrval
will be ignored.--fillval
(str, default=’INDEF’)The value to assign to output pixels that have zero weight or do not receive any flux from any input pixels during drizzling.
--weight_type
(str, default=’ivm’)The weighting type for each input image. If
weight_type=ivm
(the default), the scaling value will be determined per-pixel using the inverse of the read noise (VAR_RNOISE) array stored in each input image. If the VAR_RNOISE array does not exist, the variance is set to 1 for all pixels (equal weighting). Ifweight_type=exptime
, the scaling value will be set equal to the exposure time found in the image header.--single
(bool, default=False)If set to
True
, resample each input image into a separate output. IfFalse
(the default), each input is resampled additively (with weights) to a common output--blendheaders
(bool, default=True)Blend metadata from all input images into the resampled output image.
--allowed_memory
(float, default=None)Specifies the fractional amount of free memory to allow when creating the resampled image. If
None
, the environment variableDMODEL_ALLOWED_MEMORY
is used. If not defined, no check is made. If the resampled image would be larger than specified, anOutputTooLargeError
exception will be generated.For example, if set to
0.5
, only resampled images that use less than half the available memory can be created.--in_memory
(boolean, default=True)Specifies whether or not to load and create all images that are used during processing into memory. If
False
, input files are loaded from disk when needed and all intermediate files are stored on disk, rather than in memory.