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<p>This plugin reads electron density maps written in Fsfour format, used by
<a href="http://www.scripps.edu/pub/dem-web/toc.html">XtalView</a>. The
format is briefly described at <a
  href="http://www.csb.yale.edu/userguides/datamanip/phases/FSFOUR.html">http://www.csb.yale.edu/userguides/datamanip/phases/FSFOUR.html</a>.</p>

<h1>Feature-specific notes:</h1>

<p><b>Read-only</b>
<br>This plugin is used only to read files. VMD does not currently support
writing this file type.</p>

<p><b>Byte-order</b>
<br>Fsfour files are created using the native byte-order of the machine used
to create them. This plugin can read maps created with either
byte-order.</p>

<p><b>Symmetry Records</b>
<br>Fsfour maps may contain a collection of records that describe the
symmetry of the crystal. Since VMD does not make use of such information
currently, these records are ignored.</p>

<p><b>Unit Cell Geometry</b>
<br>Old versions of the <a
  href="http://www.scripps.edu/~cdputnam/software/cns2fsfour.html">cns2fsfour</a>
and <a
  href="http://www.scripps.edu/~cdputnam/software/ccp2fsfour.html">ccp2fsfour</a>
utilities produced files that lacked the unit cell information that was not
used by XTalView. This plugin can currently load these files, but the unit
cell will almost certainly be incorrect. Support for such files may become
deprecated, users are encouraged to upgrade the the newest versions of
these tools.

<p><b>Unit Cell Origin</b>
<br>Fsfour maps assume a periodic unit cell; therefore, each file contains
data for a unit cell beginning at the point <0, 0, 0>. 

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