| Radon parameters [message #40223] |
Mon, 26 July 2004 10:28  |
![Tim[1] is currently offline](theme/default/images/xoffline.png.pagespeed.ic.XRkd1fkXye.png "Tim[1] is currently offline")
Tim[1]
Messages: 4
Registered: June 2004
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Junior Member |
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Dear all,
This sort of question has come along before, but I'm still not able to give
the correct parameters to the RADON function.
The situation is as follows. I have 73 experimentally obtained projections
of an object, each 193 by 193 pixels. This should give me 193 sinograms,
each 193 by 73 pixels. For each sinogram, I wish to produce a
backprojection, and I can do this using the obsolete RIEMANN command, but
I'd like to do so with the RADON function eg,
IDL> bp = RADON(/backprojection, sinogram, THETA=theta, RHO=rho)
The 73 projections were taken over an angular range -70 degrees to +74
degrees, with 2 degree increments. I am thus setting 'theta' using,
IDL> theta=(2*FINDGEN(73) - 70) * !DTOR
But, what of rho? I think that this should be a vector of 73 elements, but I
can't fathom the rationale behind how it should be formed. RADON reports
that "ARRAY, RHO, or THETA dimensions are incompatible", and I'm pretty sure
the RHO's to blame.
Any advice?
Thanks,
Tim
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| Re: Radon parameters [message #40257 is a reply to message #40223] |
Sat, 31 July 2004 03:27  |
Timm Weitkamp
Messages: 66
Registered: August 2002
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Member |
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Oh, I never compared the speed of the two. I should have done that when I
changed from RIEMANN to RADON some time ago. I prefer RADON because (a) it
is the currently supported routine and (b) because I found it had more
functionality.
When benchmarking, of course you should make sure the speed difference
between the two routines isn't just due to more elaborate interpolation by
one of them. Did you check that?
Timm
On 28.07.04 at 10:40 +0100, Tim Yates wrote:
> Dear Timm,
>
> Thanks for the info. Transposing the sinogram fixed the problem.
>
> One may use RADON or RIEMANN for backprojection, but which do you find that
> there are particular advantages in using one over the other? It strikes me,
> for one thing, that my routine with RIEMANN runs faster than the equivalent
> with RADON.
>
> Best,
> Tim
--
Timm Weitkamp
Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
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