A question about data origin in densiy maps... I open a map using the python script (in IDLE):

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import VolumeData gd = VolumeData.mrc.open ( "MRC map file" )[0]

looking at the origin of this map:

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gd.origin (-135.679992676, -135.679992676, -135.679992676)

It is different than the origin reported if I open the same map file in Volume Viewer; pasted from the Volume Viewer dialog: -136.75 -136.75 -136.75 Why the difference? As to why I care, it's because if I open the map as in the python script above and then subsequently use it to compute average density values for certain structures, they are different than the average density values reported in the 'Fit Model in Map' dialog. It would give me more peace of mind if they matched... Now to start speculating on why the difference, I've seen that, internally, MRC maps define the origin in terms of a grid value, for example -64,-64,-64 in a 128x128x128 map. So the first value for the origin, as in the script method above, is calculated as if the origin is at the _center_ of the first grid point: origin[0] = -64 * step + step/2 (where step is 2.13669279804), while the second value (showing up in Volume Viewer) is simply calculated right on the grid point: origin[0] = -64 * step What's the right way to think about this? In the worst case, it's really a pretty small offset so not a big deal. Greg