[Rtk-users] Online reconstruction

[Simon Rit]

Hi,
1. Yes, this is correct. You have to know some information about your
geometry to be able to do the Parker weighting: the first angle after the
large angular gap and the delta, i.e., the size of the gap. Currently, this
is computed from the geometry. Two solutions to be able to do it online:
pass the full geometry if you know in advance or set these parameters
(needs a modification of Parker weighting class).
2. Correct. BTW, this is done for convenience but some people have
suggested to correct this.
Contributions are welcome. The best is to fork RTK on github and do a pull
request when your code is ready.
Simon


On Sat, Feb 24, 2018 at 7:21 PM, Fredrik Hellman <fredrik.hellman at gmail.com>
wrote:

> Thank you for your quick replies!
>
> The rtkinlinefdk application is very interesting. I have read it and have
> two observations:
>
> 1. The Parker short scan code is currently disabled in that application. I
> guess the reason is that it cannot compute the overscan angle without the
> full geometry, and that it has to be provided in some other way than
> through the geometry object.
>
> 2. The reconstruction processing starts when there are at least 3
> projections available (line 281), and it then starts with the second
> projection. The reason for this (I suppose) is that the angular gaps are
> computed based on adjacent projection angles, so projection angles 0 and 2
> needs to be available to properly weight projection 1. Finally (line 343),
> the first (0) and last (N) projection are backprojected, which I suppose is
> because the angular gap between projection N and 0 should be available to
> the angular gap weighting of projections 0 and N. Typically the RTK Parker
> weighting puts 0 weight for first and last projection so that the very
> large angular gap weighting (e.g. for half scans) for first and last
> projection has no effect. (Line numbers relates to commit 4198eb3 of
> https://github.com/SimonRit/RTK)
>
> Are there any current plans or ideas on how to add support for inline
> Parker weighting (and allow e.g. half scans)? If not, what is the procedure
> for contributing to the RTK project with such a Parker weighting
> implementation?
>
> Best regards,
> Fredrik
>
>
> 343
>
> 2018-02-22 15:36 GMT+01:00 Simon Rit <simon.rit at creatis.insa-lyon.fr>:
>
>> Hi,
>> Yes, you can even if you don't know the geometry in advance. The
>> application rtkinlinefdk and its code rtkinlinefdk.cxx illustrates this.
>> Best regards,
>> Simon
>>
>> On Thu, Feb 22, 2018 at 2:05 PM, Chao Wu <wuchao04 at gmail.com> wrote:
>>
>>> Hi Fredrik, If the geometry and projection angles are known in advance,
>>> I think it is possible to perform FDK online.
>>> Regards, Chao
>>>
>>> 2018-02-22 11:11 GMT+01:00 Fredrik Hellman <fredrik.hellman at gmail.com>:
>>>
>>>> Hi,
>>>>
>>>> I am wondering if it is possible to do "online" reconstruction with RTK
>>>> using FDK backprojection, i.e. that you populate the geometry object angle
>>>> by angle and backproject only one or a few projections at a time with the
>>>> geometry object not fully populated initially.
>>>>
>>>> I have seen that the backprojection can be done projection by
>>>> projection, but it seems that the geometry object must be populated with
>>>> all angles before starting. For example in the code for parker weighting,
>>>> it seems that the overscan angle is estimated based on the actual angles in
>>>> the geometry object. Also, computing the angular gap weighting done in the
>>>> 2D weighting depends on adjacent angles.
>>>>
>>>> Best regards,
>>>> Fredrik Hellman
>>>>
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