3D Design

3D Design

Simplifying the geometry of a CT scan

    • danielc358
      Subscriber

      Simplification of geometry can be done within the Ansys software. I read a material saying that by modifying an Ansys property, this decreased the number of points in the geometry, but I could not figure out what I should change in geometry to decrease the number of points, for the simplification of tomography geometry?, Is there any software literature that teaches you how to make a stable mesh?


      Best regards


      Daniel

    • peteroznewman
      Subscriber

      Daniel,


      A CT scan generates a volume of voxels that have a value in Hounsfield Units (HU). ANSYS can't read that data directly. Segmentation software creates iso-surfaces at the boundary between high and low density voxels such as bone and muscle. This boundary is what can be used to show bone only for example. Those surfaces are often made of many small triangular facets about the same size as the voxel edge. The STL file format is often used to export that surface. The STL surfaces might not enclose a volume.


      If you have an enclosed volume of a bone for example, how are you going to deal with the change in bone density from the surface to the center?


      Some software has the ability to fit b-spline (smooth) surfaces through a large number of facets. SpaceClaim has some of those abilities, such as Reverse Engineering tab, but that is not included in the Student license. There is a Merge face command, but that is much less powerful than the "Shrinkwrap" command in the Reverse Engineering tab.


      Can you show an image of what your geometry looks like at this time?


      Regards,


      Peter


       

    • danielc358
      Subscriber

      Hi Peter, good afternoon !!!


      I used the software InVesalius 3.1 to extract a CAD image and with this I have a .STL file , but the image has many faces and vertices I have to reduce the number of points to be able do the simulation, how do I decrease the number of faces and vertices without changing the shape of the image ?, If I use the command Shrinkwrap automatically reduces the number of faces and vertices ?, is there another way?


      Attached is the image of CT scan file


      Regards,


      Daniel


    • peteroznewman
      Subscriber

      Hi Daniel,


      Are you using the ANSYS Student license?  If so, you are going to have find other software to reduce the number of facets by fitting a smooth b-rep surface through the cloud of points that the STL file has represented by individual facets. The Student license for the ANSYS geometry editors have a limit of 300 faces for geometry. When you bring in an STL file, it doesn't count all the facets as geometry, but you don't want to mesh that either. 


      There are a few students on this site who have been struggling with CT data. You can read one recent discussion with Aginn, especially her last post which lists some tools to use if you need to find an alternative to SpaceClaim.


      I also struggled with SpaceClaim in the video below. Jump forward to 3 min 30 second mark for the Merge feature. This was in collaboration with Maurya.



       


      The image you show looks like a vessel. Does this represent the outer surface of the vessel?  Are you going to Shell the solid body to create a uniform wall thickness for the vessel?  Or do you have a second surface for the inside wall of the vessel?  Perhaps this is the inside wall of the vessel and the solid represents the fluid inside the vessel wall.  Please give us some more detail about what you want to analyze about this geometry.


       Regards,


      Peter

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