notice: stl-to-pa conversion accuracy improved in sltools

[David Manura]

An important change has been made in SL Tools to improve the accuracy of the STL -> PA conversion. This change now permits exact grid-unit alignment when using STL files, which previously was only really achievable with GEM, Modify, and programming approaches to geometry definition. Details are in http://simion.com/issue/339 . The change affects version 8.0.7-TEST11 (side note: the version number scheme for SL Tools has also been changed to correspond to SIMION version numbers).

 

Some screenshots are attached. The picture on the left shows two_cylinder.stl, which is a recent addition to the SIMION "geometry" example set (you can download "simion8-geometry-20110805.zip" from the "Check for Updates" button on the SIMION 8.0 main screen). The conversion was done at a very low resolution so that it's easier to observe the accuracy. It's important to note that during the conversion process I used the option "Solid strategy" = "No extra solid points" (most accurate), which causes surfaces to be treated as ideal 100% tranmission grids in the PA. It can be observed with the mouse that all the dimensions, including the inner hole radius, exactly match the original STL file (apart from the "inherent" defect at non-orthogonal angles of the cylinder renderd in a 3D rectangular PA).

 

The picture on the right shows another STL file of a single triangle with corners at vertices of a cube. Again, this was converted using the "No extra solid points" option, so the triangle is treated as an ideal 100% transmission grid. Since electrode points that are not solid points do not always display in the 3D view, in order to visualize this PA, I enabled the "Points" option. The "Points" option has been changed in the latest version to display all grid points that are electrode points but not inside the solid. (The Points feature can also be useful to visualize the grid density.) You can observe that, unlike in earlier version of SL Tools, the spacing between points is very regular, and remains so even if we don't use the "No extra solid points" option. The algorithm for rendering the has been improved and more thoroughly tested for topological properties.

 

Additional "Solid strategies" may be added later. However, "No extra solid points" will provide the best accuracy.

 

Although major new features are now only going into SIMION 8.1, I considered this more of a defect correction rather than a new feature, so it's made available in 8.0 as well. A future planned update to SL Tools, whicht will only be available in 8.1, will be to support the 8.1.x enhanced refine accuracy option hinted in http://simion.com/info/simion81.html , which will will work toward reducing the "inherent defect" mentioned above.