[Rtk-users] 3D mesh points projection onto the DRR image plane

[Simon Rit]

Hi,
The easiest is to use the projection matrices from the geometry object with
GetMatrix
<http://www.openrtk.org/Doxygen/classrtk_1_1ProjectionGeometry.html#ac848531d266395624ee8f1f328ae67d3>
which takes the projection number as a paramter or GetMatrices
<http://www.openrtk.org/Doxygen/classrtk_1_1ProjectionGeometry.html#aa00734aa99a710a163a0eb30334cbac7>
to get the full list. You can then multiply your 3D homogeneous coordinate
in image space (x,y,z,1) by multiplying it with the matrix to get the
homogenous projection coordinates (u,v,w) (so you get the actual 2D
coordinates (u/w, v/w)).
Simon

On Mon, Sep 25, 2023 at 8:29 AM Suranga W <isurusuranga.wijesinghe at gmail.com>
wrote:

> Hi,
>
> I have segmented the liver from a 3D-CT volume and created a volumetric
> mesh. I have successfully generated DRRs by using RTK tool kit. The code is
> attached below. Now what I want is that I need to project each and every 3D
> coordinates of the volumetric mesh on this DRR image plane. This means that
>  finding the corresponding 2D projection coordinate (i.e. x, y positions)
> of each vertex coordinate on the DRR image projection plane.
>
> How can I obtain the (x, y) coordinate values in the DRR image plane for a
> given 3D coordinate position? For example, I have (x,y,z) positions for
> each vertex and I want to convert into (x,y) i.e. 2D projection coordinates
> on the DRR image plane? Can you please elaborate with an example ?
>
> I have python code to project the 3D-mesh coordinates  on DRR images based
> on ITK SiddonJacobsRayTracing algorithm. However, I want to implement this
> code similar to the RTK based DRR projections. I have attached this ITK
> based DRR generation code and the point projection code which is compatible
> to this ITK-based DRR code for your further reference.  Moreover, I have
> attached sample DRR image with projected points overlaid on it that is
> based on ITK-based code.
>
> *Additional note:* The reason because I have chosen RTK since it is more
> convenient than ITK based ray-tracing algorithm when generating DRRs so
> that I’m able to generate DRRs to match the exact field of view of real kV
> planar x-ray images.
>
>
> Thanks,
>
> Surang
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