Working on imported STL mesh file
 

Hello

I have imported a mesh file in stl format which is the prfect surface mesh I require. i just need to create a volume mesh (a spherical farfield) around it. When I do so and start meshing the farfield the imported stl file automatically vanishes. I did see few threads regarding build topology etc for a similar question. But my grid topology option is not even highlighted since I import as a mesh. If I import as geometry I will not be able to have the same mesh as in the stl file and also I need to remesh entirely. Could some one give a solution to this problem?

Note: You can suggest me if any other mesh formats are compatible for my requirement!!