User's Guide

XCORRECT

Performs along-line systematic corrections on full-sized, non-geometrically corrected MSS data.

Function:

Performs along-line systematic corrections on full-sized, nongeometrically corrected MSS data from Landsat 2 through 5. The image data is corrected for the following high frequency systematic errors:
      1.  Line length adjustment
      2.  Mirror scan nonlinearity
      3.  Band-to-band offsets
      4.  Earth rotation
      5.  Detector-to-detector sampling delay
After the systematic corrections are applied, the data is resampled along-line using the specified algorithm.

Parameters:

Subcommand -CUBIC:

Cubic convolution resampling. Uses four pixels which surround the calculated floating point pixel location to determine the output pixel value.

IN
Input image. The input image is an uncorrected MSS scene created by PLENTER. It is always BYTE. Only one image may be specified at a time. The user may specify subbands. However, windowing specifications are ignored.

OUT
Output image. The output image is always BYTE. It has the same number of bands specified in the input image.

PCCALPHA(-0.5)
Parametric cubic convolution alpha parameter. Commonly used values are -1.0 and -0.5; values -3.0 through 3.0 produce reasonable results. Other values may cause unpredictable results but are permitted for experimental purposes.

INTLIM(--)
Interpolation limits (MIN,MAX). The minimum and maximum resultant intensity allowed in resampling. If NULL, INTLIM defaults to the maximum range for BYTE data type.

BACKGRND(0)
Background value. Gray level fill value assigned to all output pixels outside the boundaries of the input image.

Subcommand -BILINEAR:

Bilinear resampling. Uses two input pixels which surround the calculated floating point pixel location to determine the output pixel value.

IN
Input image. The input image is an uncorrected MSS scene created by PLENTER. It is always BYTE. Only one image may be specified at a time. The user may specify subbands. However, windowing specifications are ignored.

OUT
Output image. The output image is always BYTE. It has the same number of bands specified in the input image.

INTLIM(0,255)
Interpolation limits (MIN,MAX). The minimum and maximum resultant intensity allowed in resampling. If NULL, INTLIM defaults to the maximum range for BYTE data type.

BACKGRND(0)
Background value. Gray level fill value assigned to all output pixels outside the boundaries of the input image.

Subcommand -TABLE:

Resampling based on a table of user-entered resampling weights. Uses N pixels which surround the calculated floating point pixel location to determine the output pixel value. Sixteen is the maximum value for N. The dimension N and the resampling weights are located in INRWT.

IN
Input image. The input image is an uncorrected MSS scene created by PLENTER. It is always BYTE. Only one image may be specified at a time. The user may specify subbands. However, windowing specifications are ignored.

INRWT
Input resampling weight table file. A file containing an externally generated table of resampling weights. The resampling table is created using RTABLE.

OUT
Output image. The output image is always BYTE. It has the same number of bands specified in the input image.

INTLIM(0,255)
Interpolation limits (MIN,MAX). The minimum and maximum resultant intensity allowed in resampling. If NULL, INTLIM defaults to the maximum range for BYTE data type.

BACKGRND(0)
Background value. Gray level fill value assigned to all output pixels outside the boundaries of the input image.

Examples:

LAS> xcorrect-cubic in=needles out=needles.cor intlim=(0,127)
The image data from the uncorrected image NEEDLES is input, corrected for systematic errors, resampled using the parametric cubic convolution method, and output to NEEDLES.COR. Alpha is set to -0.5. The resulting range for resampling is between 0.0 and 127.0, and background values are set to zero.
LAS> xcorrect-bilinear in="alaska(:1 2)" out=alaska.cor backgrnd = 127
Systematic corrections are applied to the first and second bands of the uncorrected image ALASKA. The bilinear interpolation method is used for resampling. Minimum and maximum interpolation limits are the full range for the BYTE data type (0 to 255). Background areas are set to 127.
LAS> xcorrect-table in=mss.uncor inrwt=table.dat + out=mss.cor intlim=(0,127)
The uncorrected image MSS.UNCOR is processed and the image data is corrected for systematic errors and resampled using the table of user-entered resampling weights in TABLE. Minimum and maximum interpolation limits are 0 and 127. Background values are set to zero.

Description/Algorithm:

The values of the LAS input parameters and the global variables are retrieved. The existence of the associated file containing the ancillary information needed to apply systematic corrections is checked. This file is opened and the values are retrieved. Next, the weight table to be used in resampling is generated when using the -CUBIC or -BILINEAR subcommands. If the -TABLE subcommand is specified, the weight table is read from INRWT.
Systematic corrections are applied to the image data using the following equation:
The HR' value computed from this equation is the pixel location of input space for the present output sample. After HR' is computed, resampling is performed along-line using the specified algorithm and the resulting value is written to the output image.

Nonfatal Error Messages:

[xcorrect-warn] Nonfatal error encountered
A nonfatal error was encountered during processing. The image data is probably valid and therefore saved. The message that is displayed immediately preceding this message is the specific error that was encountered in a library routine.

Fatal Error Messages:

[xcorrect-fatal] Fatal error encountered
A fatal error was encountered during processing. The error message that is displayed immediately preceding this message is the specific error that was encountered.
[xcorrect-nocorr] Input image's correction file does not exist
The associated file containing the information that is needed to apply systematic corrections does not exist for the input image. The correction file should have been created with PLENTER.
[correct-notable] User-defined weight table file does not exist
The file specified for INRWT does not exist. The weight table should be created using RTABLE.
[xcorrect-notbyte] Input image is not BYTE
The data type of the input image is not BYTE.
[xcorrect-openerr] Error opening <XXX> file
An error was encountered when trying to open the specified file.
[xcorrect-rderr] Error reading <XXX> file
The associated correction file was not in the expected format, or an error was encountered when reading the correction or image file.
[xcorrect-sizerr] Input image is not a full-sized MSS scene
The input image is not a full-sized (2340 lines x 3548 samples) uncorrected MSS scene; therefore systematic corrections cannot be applied.

User Notes:

The input image must be BYTE.
Systematic corrections are only applied to a full-sized MSS scene. Thus, if the image was windowed or subsampled in PLENTER, XCORRECT cannot be used on it.
An associated corrections file must exist for the input image. This file contains the ancillary information necessary to apply systematic corrections. It is an ASCII text file created optionally by PLENTER when reading MSS-CCTX tapes. The LAS name of the file is "<XXX>;cctx.rll". The format of te RLL file consists of a text file where the first line contains the nominal line length. Subsequent lines contain the line number corresponding to the images, followed by their respective raw line lengths with the synthetic pixels removed.
Resampling weight table files may be generated with the RTABLE module. This file is used with the -TABLE subcommand.