- Chimera-users - RBVI Mailing Lists

Re: [Chimera-users] Rotation about an axis
by Thomas Goddard 21 Apr '06

21 Apr '06

Hi Jordan, Aha! It turns out I wrote code that does exactly what you want last year. It is called the symmetric molecule copies command at the bottom of the Chimera experimental features web page: http://www.cgl.ucsf.edu/chimera/experimental/experimental.html It is not distributed with Chimera yet but you can download it on that page and install it with your existing Chimera. I hate to discourage you from Python programming in Chimera but I think this is just what you need. You open one copy of your molecule and then use this "sym" command to make the hexamer. Then when you move the original copy of the molecule relative to your map, the other 5 copies automatically reposition to maintain the 6-fold symmetry. To get a more detailed description look at the "details" link on the experimental features page. The hexamer symmetry comes from the BIOMT matrices in the PDB file. This sym command treats those matrices in the coordinate system of the density map (yes, a bit weird). The key here is to make sure the symmetry axis of the density map matches the symmetry axis of the BIOMT matrices. The easiest approach is probably to make the BIOMT matrices produce a hexamer about the z-axis through (0,0,0). When you open your density map in Chimera it may not have the hexamer density centered at (0,0,0). You will need to adjust its origin so the density hexamer is centered at (0,0,0). Use the volume dialog menu entry Features / Origin and Scale to adjust the position of the lower left front corner of the map. Assuming the hexamer is centered in a 128 x 128 x 100 grid with voxel size 0.8 angstroms you would set the origin to (-50.8, -50.8, -39.6) = (-63.5 * 0.8, -63.5 * 0.8, -49.5 * 0.8). The weird 63.5 = 128/2 - .5 instead of 64 = 128/2 is easiest to understand if you think of a map that is only 2 by 2 by 2 in size. Remember to press the Enter key in one of the origin fields in the volume dialog to have the new position take effect. In any case that may still be a half voxel off depending on your map, or it may be way off. Of course you have to know the position of the center of the hexamer in your density to make this work. A way to verify that you have set the correct origin is to open 2 copies of the map -- set the map origins, then use constrained move to rotate just one copy keeping the other one fixed. It is easy then to visually see if the two copies are concentric. For convenience you can save your map as an MRC file with the new origin with the volume dialog File / Save As... menu entry. Saving a Chimera session also saves the origin in the Chimera session file (the map is not modified). I can see various troubles with using the Multiscale tool. First Multiscale low resolution surfaces are not reliably synchronized to the individual PDB models. If you change a PDB model position Multiscale won't realize it and the low resolution surface will not move to the new location. If you are using the latest Chimera snapshot (1.2224, April 10, 2006) then the problems will be even more severe because I changed the way Multiscale positions PDB models. Instead of setting the pdb_model.openState.xform it changes the atom coordinates of the model (setting atom.coord = x,y,z). All the xforms of the 6 models in a hexamer would be the same in Chimera 1.2224. This change was made to allow correctly moving individual chains of multiscale models, possible with the "movement mouse mode" feature on the experimental features web page. Lastly some clarification about Chimera's coordinate systems. First there is a global Chimera coordinates system with the x axis always horizontal relative to your graphics window, the y axis always vertical, and the z axis always pointing out of the screen at you. When you rotate models with the mouse, this coordinate system does not change -- the individual matrices positioning the models are changed. The origin of this global coordinate system is not necessarily in the center of the screen. It can be anywhere including off-screen. The global coordinates for the center of the screen are set to match the center of the bounding box of the first model you open in Chimera. Besides the global coordinate system each model has a local coordinate system. With a PDB file, the atom coordinate positions are in the local coordinate system. If you open a PDB model in Chimera and rotate it, the atom.coord x,y,z values do not change -- they are expressed in the local coordinate system which is fixed to the atoms and rotates with the model. (You can however change the atom.coord positions using Python code.) The pdb_model.openState.xform 3 row by 4 column matrix gives the rotation and translation that maps the local coordinates (e.g. a PDB atom position) into Chimera global coordinates. Other types of Chimera models like density maps are just like PDB models having a local coordinate system -- the density map grid points have unchanging coordinates in the local coordinate system. More than you wanted to know. Tom > Date: Thu, 20 Apr 2006 19:51:40 -0700 > From: "Jordan Benjamin" <jordan.benjamin(a)gmail.com> > To: "Thomas Goddard" <goddard(a)cgl.ucsf.edu> > Subject: Re: [Chimera-users] Rotation about an axis > > Ah, it looks like it still works for normal models. The weird behavior > was with a model that had been generated with the Multiscale Models > tool from crystal contacts. I still wish I understood the > global-vs-local issue better though. > > > On 4/20/06, Jordan Benjamin <jordan.benjamin(a)gmail.com> wrote: > > Thank you for your help on this. I have a further question. Basically, > I'm trying to dock into electron density the crystal structure of a > protein that forms a hexamer. I would like to be able to have six > copies of the monomer structure loaded at once, and when I move or > rotate one copy, I'd like to be able to transform the other five to > match. So, I thought the ConstrainedMove code would be a good starting > point, since what I'm trying to do is the same thing it does, just > with the rotation specified by degrees instead of by dragging the > mouse. > > After you sent the email below, I modifed the function I was writing > accordingly, and it worked. However, I'm trying to use it now, and > it's not working. I'm a little lost on debugging it, because I don't > even know what Chimera's concept of a global coordinate system is, nor > do I have any way to visually display the local origin and axis for > each object. Is there a way to do these things that you know of? Do > you know of a simple way to rotate an object X degrees around a > specified axis (relative to another object if needed)? > > If these are really hard questions and the answer is just that I > should read the source code until I figure it out, that's totally > fine. I just thought I'd ask. > > At least with Chimera the code IS available, unlike the situation with > Amira where things would be undocumented and broken, and there'd be no > way to fix them... > > Thanks so much, > Jordan > > The function I was using is as follows (yes, it's brittle and ugly, > but it's all I had time for): > def update_hexamer(ref_model,model,*rest): > origin = (0,0,0) > axis = (0,0,1) > angle_deg = 60 > > mvo = chimera.Point(*origin) > vo = ref_model.openState.xform.apply(mvo) > mva = apply(chimera.Vector, axis) > va = ref_model.openState.xform.apply(mva) > > xf_original = model.openState.xform > > for i in range(5): > xf = chimera.Xform() > xf.translate(*vo) > xf.rotate(va, angle_deg+60*i) > xf.translate(-vo.x, -vo.y, -vo.z) > model.openState.globalXform(xf) > rest[i].openState.xform = model.openState.xform > model.openState.xform = xf_original >

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Re: [Chimera-users] Sum of volume data values
by Thomas Goddard 13 Apr '06

13 Apr '06

Hi Eran, Ok, here is code to read an MRC file and print the sum of map values without using Chimera. You need Python, the Numeric Python module which handles multidimensional arrays and the VolumeData module from Chimera. Numeric is obtained from sourceforge: http://sourceforge.net/project/showfiles.php?group_id=1369&package_id=1351 The VolumeData module is in your Chimera distribution. chimera/share/VolumeData Here's an example running the script where I've set PYTHONPATH to have access to the VolumeData module: % env PYTHONPATH=/usr/local/chimera/share python2.4 volumesum2.py Sum of values of groel.mrc = 21720.8984375 Send future questions to chimera-users(a)cgl.ucsf.edu so others who have similar problems can benefit. I get that email just as fast. Tom ------- file volumesum2.py follows: # Script to print the sum of volume data values. # Does not need Chimera, just the VolumeData module and Numeric and Python. path = 'groel.mrc' # Read the MRC volume data and get the 3-D Numeric array. from VolumeData.mrc.mrc_format import MRC_Data data = MRC_Data(path) m = data.matrix() # Compute the sum of the elements of the volume matrix. import Numeric sum = Numeric.sum(m.flat) # Print the sum print 'Sum of values of', path, ' = ', sum ------- > Date: Wed, 12 Apr 2006 14:46:14 -0700 > From: Eran Shacham <eshacham(a)burnham.org> > To: Thomas Goddard <goddard(a)cgl.ucsf.edu> > Subject: Re: Sum of volume data values > > Hey Tom, > > Thanks for your reply. However, I would like to do that from within a > script I already wrote. i.e I would like to integrate a read_in method > for an MRC file, access it values and then calculate the sum. I would > like to avoid doing that by opening my file in Chimera at this stage of > the program. Can it be done by importing some of your code? > > Thanks, > Eran.

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Sum of volume data values
by Thomas Goddard 12 Apr '06

12 Apr '06

Hi Eran, You can open your MRC file in Chimera, then open the following script "volumesum.py" which contains Python code to have the sum of all the volume values printed. Use menu entry File / Open to open both files. If you want to do this many times I can give you a modified version that creates a Chimera menu entry (under the Tools menu) that runs the script. Tom ------------ File volumesum.py follows: # Script to print the sum of volume data values. # Get the volume dialog object import VolumeViewer d = VolumeViewer.volume_dialog() # Get the volume data currently shown by the volume dialog dr = d.focus_region m = dr.full_matrix() # Compute the sum of the elements of the volume matrix. import Numeric sum = Numeric.sum(m.flat) # Print the sum to the reply log dialog. message = 'Sum of values of %s = %.6g' % (dr.full_name(), sum) print message # Display the reply log dialog. from chimera import dialogs dialogs.display('reply') ------------- > Date: Wed, 12 Apr 2006 13:52:26 -0700 > From: Eran Shacham <eshacham(a)burnham.org> > To: Thomas Goddard <goddard(a)cgl.ucsf.edu> > Subject: Reading mrc files > > Hi Tom, > > Can I use Chimera's code for reading in mrc files? Essentially, I would > like to read in an mrc file and access its values. It is a mask file, > and I simply need to add up it values. Any suggestions on how to do that > easily with a Chimera module? > > Cheers, > Eran

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Volume series tool
by Thomas Goddard 12 Apr '06

12 Apr '06

I wrote a Chimera tool to display sequences of volume data sets. They are displayed one at a time like a movie and a slider lets you choose any particular volume. It is intended for looking at 3-D optical microscopy time series, or a sequence of single particle density map reconstructions. Available on the Chimera experimental features web page: http://www.cgl.ucsf.edu/chimera/experimental/experimental.html Tom

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Rotation about an axis
by Jordan Benjamin 11 Apr '06

11 Apr '06

I'm trying to rotate a model about a specified axis and origin (preferably in global coordinates). I would like the rotation to be applied on top of whatever transformations have been applied already. I've looked at the documentation, including the programmer's FAQ and the source code for ConstrainedMove. I couldn't figure out how to do this, so I wrote the following function based on the ConstrainedMove code to do the rotation relative to another model: def rotate_around_model_axis(ref_model, model, origin, axis, angle_deg): mvo = apply(chimera.Vector, origin) vo = ref_model.openState.xform.apply(mvo) mva = apply(chimera.Vector, axis) va = ref_model.openState.xform.apply(mva) xf = chimera.Xform() xf.translate(vo) xf.rotate(va, angle_deg) xf.translate(-vo) model.openState.globalXform(xf) But, this doesn't seem to work as I'd intended. Is there a way to do this? Also, I'm a little confused about the coordinate system. It seems like the concept of a global coordinate system may not apply in Chimera the way I'm used to (like in Amira for example) since the camera is fixed. Is this true, or am I totally lost? Thanks in advance for any help you can provide. Jordan

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Newbie Questions
by Shafrir, Yinon (NIH/NCI) [F] 11 Apr '06

11 Apr '06

Hi there! I have two questions regarding using Chimera. How do you break a molecule to different models using the command line? I have a protein composed of 4 chains. It loads as one piece and designated model 0 I then select a single chain and I want to designate it as a new model. How do I do that using the command line (so I can write a script)? Also, when I select the chain and use the write command in this manner "write selected su1.pdb" the save dialog box pops up (even though I designated a filename) When I try "write selected 0 su1.pdb" nothing happens. My other question is: How can you force chimera to assign secondary type display to residues without editing the PDB file first? Say I want to show 30 residues that are not detected by ksdssp as beta sheets. Still, I want to represent them as beta sheets. Do I need to edit the pdb file? Best regards Yinon Shafrir

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Axis display
by Jordan Benjamin 10 Apr '06

10 Apr '06

Is there a convenient way to display the axes of the coordinate system (and preferably the origin)? Forgive me if this is addressed in the documentation, but I wasn't able to find it. Thanks, Jordan

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Collaboratory session
by Eduardo Sanz Garcia 10 Apr '06

10 Apr '06

I have been trying to set up a collaboratory session, but I could not see the model. I was able to chat and to see the pointer of the other person, anything else. Any idea? How can I know if it is a problem caused by the firewall?

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Move atoms with mouse
by Thomas Goddard 07 Apr '06

07 Apr '06

I put a tool on the Chimera experimental features web page that enhances the standard rotation and translation mouse modes (left and middle mouse buttons) to enable moving helices, strands, turns, PDB chains, any selected set of atoms, or multiscale model chains. http://www.cgl.ucsf.edu/chimera/experimental/experimental.html The molecular pieces are translated or rotated by dragging them with the mouse. It requires Chimera version 1.2206 or newer, and that is only available for Macintosh computers right now. Tom

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Newbie Questions
by Shafrir, Yinon (NIH/NCI) [F] 07 Apr '06

07 Apr '06

Hi there! I have two questions regarding using Chimera. How do you break a molecule to different models using the command line? I have a protein composed of 4 chains. It loads as one piece and designated model 0 I then select a single chain and I want to designate it as a new model. How do I do that using the command line (so I can write a script)? Also, when I select the chain and use the write command in this manner "write selected su1.pdb" the save dialog box pops up (even though I designated a filename) When I try "write selected 0 su1.pdb" nothing happens. My other question is: How can you force chimera to assign secondary type display to residues without editing the PDB file first? Say I want to show 30 residues that are not detected by ksdssp as beta sheets. Still, I want to represent them as beta sheets. Do I need to edit the pdb file? Best regards Yinon Shafrir

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