AUTOSHIFT

Description

AUTOSHIFT shifts the position of an image by modifying its extents to ensure pixel alignment with a reference image. It is assumed that both images have a misalignment of only a few pixels and were acquired using the same viewing geometry. AUTOSHIFT prepares the images used as input to any of the coherent change detection algorithms functions. To co-register non-complex SAR images, it is recommended that you run ORTHO instead.

Parameters

autoshift(fili, filref, dbic, filo, searchr, numtiles)

Name	Type	Caption	Length	Value range
FILI *	str	Input complex SAR image	1 -
FILREF *	str	Reference complex SAR image	1 -
DBIC	List[int]	Input SAR image channels	0 -
FILO *	str	Output shifted SAR image	1 -
SEARCHR	List[int]	Search radius (pixels)	0 - 1	Default: 16
NUMTILES	List[int]	Number of tiles (x-dimension, y-dimension)	0 - 2	Default: 4

* Required parameter

Parameter descriptions

FILI

Specifies the name of the input image file to be shifted. The specified image must have the same georeferencing and pixel size, and at least some overlap with the reference image file.

The input image must be a data set that has already been imported into the PCIDSK (.pix) format by SARINGEST, or it may be the key file name of any GDB-supported POLSAR data set in its distribution format. The specified image must have the same georeferencing and pixel size, and at least some overlap with the reference image file.

FILREF

Specifies the name of the file that contains the reference image data. This reference image must have the same geocoding and pixel size as the input test image file.

DBIC

Specifies the list of input channels to be processed. The specified channels must exist for the test and reference images, and must be comparable; that is, they must have the same data type and polarization. By default, all channels from the input test image (FILI) are used to compute the correlation, and output to the defined output file (FILO).

FILO

Specifies the name of the output file that is created. This file will contain the same number of channels as the specified input channels.

The specified file must not already exist.

SEARCHR

Specifies the distance, in pixels, in the X- and Y-directions over which the search for the best match between the reference and test image will be conducted. The value must be equal to or greater than the maximum offset between the images, in pixel units.

NUMTILES

Specifies the number of tiles into which the overlap area will be divided, in the X- and Y-directions; for example, "4,4" specifies four tiles across and four tiles down. The tiles should all contain valid image data values (non-background pixels).

Details

AUTOSHIFT shifts a test image by modifying its geocoding extents to guarantee pixel alignment with the reference image. To preserve the original data, no resampling is applied to the test image file. The offset is computed based on the highest correlation of complex and/or intensity values of all pixels in the search window. This function supports any polarimetric (single, dual, full polarimetric) data set from all acquisition modes. The function is NoData-aware; which means any pixel values defined as 'NoData' in the metadata will be ignored. The output image file retains all the metadata from the input test image file.

Example

This example changes the geocoding coordinates of the most recent image based on a reference image. The input image background value (NODATAVAL) is 0 and has been defined in the metadata of the input file.

from pci.autoshift import autoshift

fili	= "rsat2_FQ15_sep19.pix"	# Input image to be shifted
filref	= "rsat2_FQ15_sep25.pix"	# Reference image filename
dbic	=	[]	# Uses all input image channels to compute the correlation
filo	= "rsat2_FQ15_sep19_shifted"	# Output file name
searchr	= []
numtiles= [4,4]					#Use 4 tiles in the X- and Y-directions

autoshift(fili, filref, dbic, filo, searchr, numtiles)