Hi Jianhao, That “center” button in the Coordinates section fills in the origin index as the center of your map, with values (grid dimensions - 1)/2. I had a test map with dimensions 35 26 30 and when I clicked that button it filled in the origin index values as 17 12.5 14.5. To do the same thing as that button, you could figure out the values from your map’s grid dimensions and specify them with the “originIndex” option of the “volume” command. <http://www.rbvi.ucsf.edu/chimera/docs/UsersGuide/midas/volume.html#dimensions> However, as Tom mentioned, the center of the map grid might not be exactly the same as center of symmetry. If they’re different and you know the grid indices of the center of symmetry, you would use those values instead. Chimera doesn’t have a way to figure them out automatically. Best, Elaine ----- Elaine C. Meng, Ph.D. UCSF Chimera(X) team Department of Pharmaceutical Chemistry University of California, San Francisco