Hi Jie, You want to save a map that has been rotated relative to another map so that when you open both maps later they align. The difficulty is that the common map file formats like MRC and Spider don't have any place in the file header to specify a rotation. There are two ways to work around this limitation. One is that Chimera does some special trickery and puts the rotation information into a "label" in MRC map files so that when it later reads the file it can restore it in the right position. The trouble is that no other software will recognize that rotated position -- only Chimera. Another difficulty is that Chimera won't record the rotated position when you fit one map in another. The reason for that is because Chimera saves the rotation of the map grid relative to the maps local coordinate system. But fitting doesn't change the orientation of the grid -- instead it moves the local coordinate system (the map coordinate axes move instead of the data moving). Each map has its own set of coordinate axes. I think it would be pretty easy to add a "save relative to" option to the Same Map As... dialog that would take account of both types of rotation. But again, the orientation would only be restored by Chimera. The second method is to resample the rotated map on the grid of the map you fit into and save that resampled map. This will allow other software to open the maps and show the correct alignment. The drawback here is that the resampled map may have degraded quality since it interpolated the original map (trilinear interpolation). The Chimera command to do that looks like vop resample #3 onGrid #2 Here #3 is the id number (shown in Favorites / Model Panel or the volume dialog) of the rotated map that was fit into map #2. This will make a new map that you can save and it will align with map #2 when opened in another session or with other software since they share identical grids. http://www.cgl.ucsf.edu/chimera/docs/UsersGuide/midas/vop.html#resample Tom

Hi Tom,

Hope this email finds you well. This is Jie from Joachim Frank's lab. We met at the UCSF molecular animation workshop.

I am writing about the "save map as" function in Chimera. Is there a way to save map relative to another map (like the option available in "save PDB")? The fitting algorithm ("fit in map" function) in Chimera is very good, and I sometimes use it to align two density maps. However, I couldn't save the density map after it was shifted. If there's no such option, is it possible to add it?

Best regards,

-Jie