Hi, I am a beginner in using Chimera. I have a simple question for you experts and I really appreciate any guide for me. I am working on a project needs to create a one-to-one mapping between MRC grid and PDB atoms. For example, from the PDB file, I know the physical coordinates of each atom. I want to know whether each atom is out of the 3D volume of MRC or not. If it is inside the volume, I hope to know which voxel grid this atom is in. I have figured out the mapping between the physical origin of PDB system and its grid index in MRC using Chimera Volume Viewer -- > Features ---> Coordinates ----> Origin Index. But I am not sure whether the information of 'Rotation axis' is also very important, which is usually [0,0,1] in Chimera Volume Viewer -- > Features ---> Coordinates ----> Rotation axis. Thank you very much. Best, Rongjian