skew

IPW User Command
Category - Image Transformation


NAME

skew - skew the lines of an IPW image

SYNOPSIS

skew [ -a angle ] [ -h ] [image]

DESCRIPTION

skew copies image (default: standard input) to the standard output, skewing the origin of successive lines by a specified angle.

OPTIONS

-a angle
Introduce horizontal skew such the the left edge of the output image is tilted "angle" degrees clockwise from vertical. The resulting "dead space" in the output image is 0-filled. A skew header is written to the output image.

If -a is not specified, then the skew indicated by the input skew

header is removed.

-h
ignore input skew header. This allows an image to be skewed more than once, e.g. during rotation by shearing.

-h
may not be specified unless -a is also specified.
-P nthreads
number of threads to use, default=1 (parallel processing)

OPERANDS

[image]
image

EXAMPLES

The command:

	skew -a 30

causes the following transformation:

	+-----------+		+---------------+
	|           |		|000/          /|
	|   input   |		|00/  output  /0|
	|   image   |		|0/   image  /00|
	|           |		|/          /000|
	+-----------+		+---------------+

FILES

     $WORKDIR/skewNNNNN
     	Temporary copy of all input headers.

DIAGNOSTICS

image is already skewed

-a was specified, and the input image contains a "skew" header.

image is not skewed

-a was not specified, and the input image does not contain a "skew" header.

band band has no skew header different skew angles: bands 0, band

If -a is not specified, then all input bands must have a "skew" header, and they must be the same.

RESTRICTIONS

The skew angle given by -a must be between -45 and 45 degrees.

If -a is specified then the input image must NOT have a skew header, unless -h is also specified, and a "skew" header is written to the output image.

If -a is NOT specified then the input image must contain a "skew" header with the same skew angle for all bands. The skew indicated by this header is removed from the output image, and no "skew" header is written to the output image.

HISTORY

Jul 1990
Written by James Frew, UCSB. Base IPW routine (Frew, 1990)
Apr 1993
Converted to ANSI C, ran through Purify. Dana Jacobsen, ERL-C.
Nov 2015
Read in full image before transpose, parallel, allow skew.c to be called as a stand alone function. Scott Havens. USDA-ARS.

BUGS

None that we know of

SEE ALSO

IPW
flip, gviewf, horizon, rotate, transpose, viewf

Frew, J., 1990. The Image Processing Workbench. Ph.D. Thesis, Department of Geography, University of California, Santa Barbara, CA, 382pp.


IPW documentation / Last revised 9 November 2015 / IPW web site