geom Documentation

geom - Geometric transformation of image planes in an ISIS cube file
"geom" performs geometric operations that change the spatial
relationships between points within image planes in an ISIS cube.  The
overall effect is that of printing each image plane on a rubber sheet,
stretching the rubber sheet, and then tacking it down at various
points.

"geom" works in concert with geometric handling programs (like "nuproj",
plansinu, planorth, etc.) which define the spatial transformation
relationship between the input and output image planes.  These programs
generate a file, known as the TFILE, which is read by the "geom"
program.  The TFILE defines the spatial relationship between the input
and output image planes.

Two separate algorithms are required for a geometric operation.  First,
there must be an algorithm to define the spatial transformation.  This
algorithm specifies the "motion" of each pixel as it "moves" from its
initial to its final position.  The second requirement for a geometric
operation is an algorithm for the interpolation of pixel values.  "geom"
offers a choice of two algorithms for pixel interpolation.  In the
simplest pixel interpolation scheme, NEAREST NEIGHBOR, the value of the
output pixel is taken to be that of the input pixel nearest to the
mapped position.  This is computationally simple and produces acceptable
results in most cases.  However, nearest neighbor interpolation can
introduce artifacts in images containing fine structure whose pixel
values change significantly over short distances.  In such cases the
BILINEAR option makes a better choice.  This interpolation scheme uses
the four pixels closest to the mapped position to determine the density
value of the output position.

All core planes in the cube are processed with the same transformation
and pixel interpolation algorithm.  All backplanes are always processed
with the NEAREST_NEIGHBOR pixel interpolation algorithm, regardless of
the pixel interpolation scheme chosen for the core planes, because back-
plane data is often discreet instead of continuous.  Sideplanes and
bottomplanes are not processed by "geom", nor are they passed through to
the output file.

The output pixel type is always the same as the input pixel type.

Programmer:  Debbie Cook, U.S.G.S., Flagstaff

Input cube file name
  (default extension is .cub)

NONE

Output cube file name
  (default extension is .cub)

NONE

Transformation file
(no default extension)

tfile.dat

Density interpolation scheme
(NEAREST_NEIGHBOR or BILINEAR)

BILINEAR

Minimum number of valid pixels
in neighborhood
(for BILINEAR only)

4

First work file

geom1.WRK

Second work file

geom2.WRK

ADDITIONAL NOTES:

Parm	Description
FROM	Input cube file name. If the file extension is omitted, then ".cub" will be assumed.
TO	Output cube file name. If the file extension is omitted, then ".cub" will be assumed.
TFILE	Transformation file created by another program, such as "nuproj" or "plansinu". The name given in these programs for the TFILE for this image is the same name that should be used here.
DNINTERP	This is the interpolation scheme to use to calculate the density value for the output pixel. NEAREST_NEIGHBOR - uses the input pixel nearest to the mapped position. BILINEAR - uses the four input pixels closest to the mapped position to interpolate the output density with a four-point fit. The following equation is used: output dn = c1*line + c2*samp + c3 + c4*line*samp, where each coefficient is determined by the density values of the four surrounding pixels and line and samp are relative to the top left pixel of the four input pixels.
MIN_VALS	This is the minimum number of valid pixel values required to generate a valid pixel value when using the bilinear interpolation. MIN_VALS= 1 will cause a valid pixel value to be output if any one of the four closest pixels in the input file that map to the output position are valid. A value of "4" will require that all four of the closest pixels in the input file that map to the output position be valid.
WORK1	This is the first scratch file created by "geom" for processing the input file. It is deleted after the second work file is completed. The space required for this file is approximately the size of the FROM file.
WORK2	This is the second scratch file created by "geom". It is deleted when the program ends. The space required for this file is approximately the size of the TO file.