Hello Charalampos,
I understand that you would like to specify the starting position of streamlines so that the lines do not pass through the geometry in the image.
I am not sure how you are getting your geometry into MATLAB. Are you just displaying an image, or have you actually imported the CAD model data? Whichever method it is, I will assume that you have axes set up proportional to the size of the object, and the equations necessary to calculate the streamlines at any point.
The "streamline" function, among others, all require you to specify the points at which to start the stream trace. See this page in the documentation for more information. Their example is in 3-D, but similar applications work for 2-D as well.
You can choose the locations of the streamline display to be outside of the geometry (based on prior knowledge of the CAD model). Alternatively, you could choose starting positions uniformly across the image, and then remove any rows of data that contain points inside the geometry. You would need some kind of equation or polygon approximation of the geometry to be able to use this method though.
I hope this helps with your streamline visualization. If you need further assistance, consider contacting MathWorks Technical Support with more information on how you created your model, and what you would prefer the streamline display to look like.
-Cam
