.. _Isovolume operator:

Isovolume operator
~~~~~~~~~~~~~~~~~~

.. _isovolume_operator_example:

.. figure:: images/isovolume_example.png
   :width: 60%
   :align: center
   
   Isovolume Operator Example

The Isovolume operator creates a new unstructured mesh using only cells and
parts of cells from the original mesh that are within the specified data range
for a variable. The resulting mesh can be used in other VisIt plots. You might
use this operator when searching for cells that have certain values. The
Isovolume operator can either use the plotted variable or a variable other
than the plotted variable. For instance, you might want to see a Pseudocolor
plot of pressure while using the Isovolume operator to remove all cells and
parts of cells below a certain density. An example of a plot to which an
Isovolume operator has been applied is shown in
.

Using the Isovolume operator
""""""""""""""""""""""""""""

.. _isovolume_window:

.. figure:: images/isovolumewindow.png
   :width: 60%
   :align: center
   
   Isovolume Attributes Window

The Isovolume operator iterates over every cell in a mesh and determines which
parts of the cell, if any, contain a value that falls within a specified data
range. If any parts of the cell are within the specified data range, they are
kept as part of the operator's output. The Isovolume operator uses an
isosurfacing algorithm to determine the interfaces where cells should be split
so the interfaces for neighboring cells are all continuous and fairly smooth.
To specify a data range, type new upper and lower bounds into the
**Lower bound** and **Upper bound** text fields in the
**Isovolume Attributes Window**, which is shown in 
:numref:`Figure %s<isovolume_window>`.

The variable that the Isovolume operator uses does not necessarily have to
match the plotted variable. If the plotted variable is to be used, the
**Variable** text field must contain the word: default. If you want to make
the Isovolume operator use a different variable so you can, for example, plot
temperature but only look at regions that have a density greater than 2g/mL,
you can set the Isovolume's variable to temperature. To make the Isovolume
operator use a different variable, select a new variable from the **Variable**
variable button in the **Isovolume Attributes Window**.

If you apply this operator to a plot that does not operator on scalar variables
such as the Mesh or Subset plots, be sure to set the variable because the
default variables for those plots is never a scalar variable. Without a scalar
variable, the Isovolume operator will not work.

.. spelling::
    mL 
