Robert Koslover
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                                                Posted:
                            
                                8 years ago                            
                            
                                07.07.2017, 22:58 GMT-4                            
                        
                        
                                                    Create another cylinder that intersects with your cylinder, and execute an intersection (Boolean) operation between them.  Delete any leftover geometry elements that you don't want.                                                
                                                
                            Create another cylinder that intersects with your cylinder, and execute an intersection (Boolean) operation between them.  Delete any leftover geometry elements that you don't want.                        
                                                
                                                                                                            
                                             
                        
                        
                            
                                                                                        
                                Edgar J. Kaiser
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                                                Posted:
                            
                                8 years ago                            
                            
                                08.07.2017, 03:19 GMT-4                            
                        
                        
                                                    You have to define what a circle on the cylinder surface is for you. A circle is inherently a flat (2D) curve that doesn't exist on a curved surface.
Robert's approach projects a circle on a cylinder surface but this curve does not fulfill a circle's implicit definition in 3D: 
 
If you need something like this you may try to find a suitable parameterization. However , in turn the projection of such a curve on a 2D plane will no longer look like a circle. 
Cheers
Edgar
--
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com                                                
                            You have to define what a circle on the cylinder surface is for you. A circle is inherently a flat (2D) curve that doesn't exist on a curved surface.
Robert's approach projects a circle on a cylinder surface but this curve does not fulfill a circle's implicit definition in 3D: 
[math] (x - x_0)^2 + (y - y_0)^2 +(z - z_0)^2 = r^2[/math]
If you need something like this you may try to find a suitable parameterization. However , in turn the projection of such a curve on a 2D plane will no longer look like a circle. 
Cheers
Edgar
--
Edgar J. Kaiser
emPhys Physical Technology
http://www.emphys.com