PJ AT - Project - 3D volume using exponential Attenuation

PURPOSE

Computes a projection of a 3D density distribution along two specified angles (azimuth angle, PHI, and tilt angle, THETA), using the formula:

p(i) = SUM [ p(i) + exp(-a*v(i,z))+ b*v(i,z) ]
over z

Basic idea: The object consists of slices, which absorb the light comming from the back (exponential part) and also illuminate the following slice (additive part).

USAGE

.OPERATION: PJ AT

.INPUT VOLUME: PIC001
[Enter the name of the file whose projection is to be computed. Should be a cube!]

.PROJECTION SAMPLE DIM.: 110
[Enter the sample dimension for the projection file equal to, or smaller than, the volume sidelength. Arbitrary dimensions can be used.]

.OUTPUT FILE: PRJ001
[Enter the name of the file where the projection is to be stored.]

.AZIMUTH ANGLE(PHI): 45.5
[Enter the azimuth angle, in degrees.]

.TILT ANGLE(THETA): -30.0
[Enter the tilt angle, in degrees.]

.SCALE FACTS IN EXP, SUM: 1., 1.
[Enter scale factors: the first is 'a' and the second is 'b' in the formula above.]

.THRESHOLD VALUE (BELOW), ADD. CONST: 0.1, 0.5
[Enter threshold value. Values in the volume below the threshold will not be used in the calculation of the projection. The additive constant is added to each voxel that has passed the threshold criterion. The effect of this value is a steeper transition between background and particle.]

NOTES

1. Not tested!