INP=(PIC,INT) PIC is an image.
INT is an IBIS interface file
containing columns which give point
locations in the image PIC.
No output file is used but the
second input file is modified.
COLS=(L,S,T,S) The integers L,S specify the file
columns which contain the line and
sample coordinates to be looked up.
Column T is used to store the resultant
grey values. Optional column S stores
the sigma (0 means don't store sigma)
REJECT=N The integer N specifies that if N or
more grey values in a rectangle are
less than or equal to the parameter THR-
EJECT, then a "no information" marker is
stored instead of a grey value. The
marker is the value -999.0 .
THREJECT=M The integer M specifies the image value
below which pixels are counted towards
the reject count threshold.
WINDOW=W specifies that a window of size W points
square is used to obtain the average
brightness value. The window will be
centered on the line, sample coordinate
even if it is fractional. W is an
integer (default value 10). W cannot be
larger than 1001.
BILIN specifies bilinear option. When the
WINDOW is 2 then this is normal bilinear
interpolation on the surrounding four
pixel values. When WINDOW is greater
than 2 then the edge pixels of the
window are interpolated in a bilinear
fashion and the inside pixels of the
window are given full weight. THIS IS
THE RECOMMENDED OPTION.
NOIN specifies no-interpolation option. The
DN-value at the location nearest to the
one specified by line-sample from the
columns L, S will be read and stored in
the column T.
INTEGRAL specifies no-interpolation option using
a window. The window size must be odd.
The pixel nearest to the line-sample
location is the center of the window.
The z-value will be the average of the
pixels in the window.
SPOT specifies no-interpolation option using
a window. The window size must be odd.
The pixel nearest to the line-sample
location is the center of the window.
The z-value will be the average of the
pixels in the window that fall within
a circular radius of the center. The
radius is WINDOW/2.
SPOT_R same as SPOT except that the pixels are
weighted inversely with distance+1. So
for the case of line-sample at a pixel
the center pixel has weight 1.0, the
four neighbors weight 0.5, the four
diagonals weight 0.414, etc. This
algorithm works well for fractional
line-sample locations.
SPOT_R2 same as SPOT_R except that the pixels
are weighted inversely with distance+1
squared.
Use to vary the spot_r or spot_r2 formula. The formulas use distance from the pixel center (which could be zero) so a constant SPOTFAC is added to guarantee non-zero. If it is small, a high emphasis is placed on a nearby point and other points will have little effect. Larger values will de-emphasize the nearest point and will, in the limit, tend towards the overall average of the pixels. The default value of 2.0 is suggested.
Data logged from the DTED disk might have this value problem. You can tell by using the HIST program on the data set. The input value is compared to -5000. If larger, then the value is not changed. If smaller, then -(32768 plus the value) is used in place of the value. So -32767 is -1, -32766 is -2, etc.