Thank you,
One more confirm. Is the "t" in ray["t"] the built-in field (like Density) or the derived field that I need to make in my own?

Junhwan



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Jun-Hwan Choi, Ph.D.
Department of Physics and Astronomy, University of Kentucky
Tel: (859) 897-6737        Fax: (859) 323-2846
Email: jhchoi@pa.uky.edu   URL: http://www.pa.uky.edu/~jhchoi
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