Hello Lorenz,
But, if you use the command 'measure mapstats' to get summary statistics of map values (
https://www.cgl.ucsf.edu/chimerax/docs/user/commands/measure.html#mapstats ), you will notice that different maps have very different distributions of voxel values. This is because: 1) cryoEM maps are not on an absolute scale (the voxel values totally depend on the pixel values in the original micrographs, which will be different from dataset to dataset); and 2) box sizes are arbitrary, which affects the mean and median voxel values because you never have the same ratio of voxels containing background versus voxels containing signal.
So, setting contour levels like this might not work exactly as you want. Always check visually!
I have had no problem choosing contour levels visually as best as I can, and reporting the absolute contour level for each map when writing about such comparisons.
If you are comparing similar structures at similar resolutions, say for example an apo structure versus the same with a bound ligand, then one way to obtain comparable contour levels could be as follows:
1) choose a "reference" map, set its contour level interactively to something adequate for the features you are looking at, and note the absolute level (from the volume viewer) in case you need to set it again later after other changes
3) now on your other map, adjust the contour level visually until it roughly matches the reference map, measure the volume, and adjust the contour level finely (fine adjustments are easier with the 'volume level' command than manually with the slider) until the measured volume matches the one you had for the reference map in step 2
4) note the absolute contour level of this other map from the volume viewer: it is likely not identical to the one of the reference map, despite both maps now at a contour enclosing the same volume
I hope this helps,
Guillaume
Dear ChimeraX-Team and all,
I want to visualize multiple cryoEM maps in a comparative manner. Therefore, I would like to display them with a threshold level of e.g. 90% their maximum voxel value.
Is this possible in chimerax? Any help would be greatly appreciated. Thank you.
Best,
Lorenz
VARNING: Klicka inte på länkar och öppna inte bilagor om du inte känner igen avsändaren och vet att innehållet är säkert.
CAUTION: Do not click on links or open attachments unless you recognise the sender and know the content is safe.