Hello, I am trying to do something seemingly simple, but can't figure out what I am doing wrong. I have an mrc map open as model #1, moved the center of rotation somewhere, then generated a sphere with: shape sphere radius 30 center cofr I got a sphere as model #2, good. Then I want to turn this sphere into a mask, which I try doing like this: volume onemask #2 ongrid #1 At which point I get this error: Expected a density maps specifier or a keyword The documentation of 'volume onemask' says it needs a surface specification as the first argument, and the model panel shows that there is no surface associated to the sphere (then why/how is it displayed? not sure), so that all seems to make sense. And I am stuck at this step: how do I turn this sphere into a surface so I can generate a volume from it? I read the documentation for 'surface', 'volume' and 'shape' but can't find anything to solve this problem. Thank you in advance, Guillaume När du har kontakt med oss på Uppsala universitet med e-post så innebär det att vi behandlar dina personuppgifter. För att läsa mer om hur vi gör det kan du läsa här: http://www.uu.se/om-uu/dataskydd-personuppgifter/ E-mailing Uppsala University means that we will process your personal data. For more information on how this is performed, please read here: http://www.uu.se/en/about-uu/data-protection-policy