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.TH CEN 1 "Ultrasonics Laboratory"
.SH NAME
cen - Find the Center of CRC Scanner Data
.SH SYNOPSIS
cen [-fpec] [n=100] [k=100] [if=for003.dat]
.SH DESCRIPTION
This program finds the center of real-world projection
data by comparing the first and last projections.
This is needed since the center of rotation does not
correspond with the center of each projection.
In parallel data from the
CRC scanner the two projections are almost 180 degrees apart
This program should give a very accurate estimate of the
center of rotation for the scanner.
.PP
This program first flips the last
projection (unless the 
.B -f
flag is set)
and then computes the distance between the
two projections as they are moved past each other.
The center of the scanner is indicated by the
smallest distance.
The resulting array of distances will be saved in the file
.B err
if the 
.B -e
flag is used.
.PP
The output from this program can be used
on the command line for
.B back
(1) to indicate the actual center of rotation.
The output from the program is a single floating point
number if the
.B -c
flag is used.
This option is useful in shell files where the result
of this program will be used to modify the back projection
and/or filtering.
In addition the program also prints
out a summary of the parameters unless the
.B -p
or the
.B -c 
flags are present on the command line.
.PP
The scanner parameters can also be set from the command line.
The number of detectors is set with the
.B n=
option.
One hundred detectors are used unless this parameter is set.
The
.B k=
option sets the number of projections in the scan.
Normally 100 projections are used.
The projection data is read from the file
.B for003.dat
unless the 
.B if=
flag is used.
The data should be organized as
.B k
projections of
.B n
single precision data points.
.SH FILES
.TP 13
for003.dat
is the default input file.
See the 
.B if=
option above.
.TP
err
distance as projections are compared.
See the 
.B -e
flag above.
.SH SEE ALSO
Crawford, Carl, 
"Multipath artifacts in Ultrasonic Transmission Tomography,"
Purdue University Electrical Engineering Department Technical Report,
TR 81-43,
December 1981, Appendix.
.br
Also see
.B back
(1)
.SH DIAGNOSTICS
An error message is printed if the input file
cannot be opened or if all the projection data
can't be read.
.SH BUGS
No indication is given if the first and last projections
do not match.