5. Geometry Plotting Specification – plots.xml

Basic plotting capabilities are available in OpenMC by creating a plots.xml file and subsequently running with the --plot command-line flag. The root element of the plots.xml is simply <plots> and any number output plots can be defined with <plot> sub-elements. Four plot types are currently implemented in openMC:

• slice 2D pixel plot along one of the major axes. Produces a PNG image file.

• voxel 3D voxel data dump. Produces an HDF5 file containing voxel xyz position and cell or material id.

• wireframe_raytrace 2D pixel plot of a three-dimensional view of a geometry using wireframes around cells or materials and coloring by depth through each material.

• solid_raytrace 2D pixel plot of a three-dimensional view of a geometry with solid colored surfaces of a set of cells or materials.

5.1. <plot> Element

Each plot is specified by a combination of the following attributes or sub-elements:

id:

The unique id of the plot.

Default: None - Required entry

filename:

Filename for the output plot file.

Default: “plot”

color_by:

Keyword for plot coloring. This can be either “cell” or “material”, which colors regions by cells and materials, respectively. For voxel plots, this determines which id (cell or material) is associated with each position.

Default: “cell”

level:

Universe depth to plot at (optional). This parameter controls how many universe levels deep to pull cell and material ids from when setting plot colors. If a given location does not have as many levels as specified, colors will be taken from the lowest level at that location. For example, if level is set to zero colors will be taken from top-level (universe zero) cells only. However, if level is set to 1 colors will be taken from cells in universes that fill top-level fill-cells, and from top-level cells that contain materials.

Default: Whatever the deepest universe is in the model

origin:

Specifies the (x,y,z) coordinate of the center of the plot. Should be three floats separated by spaces.

Default: None - Required entry

width:

Specifies the width of the plot along each of the basis directions. Should be two or three floats separated by spaces for 2D plots and 3D plots, respectively.

Default: None - Required entry

type:

Keyword for type of plot to be produced. Currently “slice”, “voxel”, “wireframe_raytrace”, and “solid_raytrace” plots are implemented. The “slice” plot type creates 2D pixel maps saved in the PNG file format. The “voxel” plot type produces a binary datafile containing voxel grid positioning and the cell or material (specified by the color tag) at the center of each voxel. Voxel plot files can be processed into VTK files using the openmc.voxel_to_vtk() function and subsequently viewed with a 3D viewer such as VISIT or Paraview. See Voxel Plot File Format for information about the datafile structure.

Note

High-resolution voxel files produced by OpenMC can be quite large, but the equivalent VTK files will be significantly smaller.

Default: “slice”

All <plot> elements must contain the pixels attribute or sub-element:

pixels:

Specifies the number of pixels or voxels to be used along each of the basis directions for “slice” and “voxel” plots, respectively. Should be two or three integers separated by spaces.

Warning

If the aspect ratio defined in pixels does not match the aspect ratio defined in width the plot may appear stretched or squeezed.

Warning

Geometry features along a basis direction smaller than width/pixels along that basis direction may not appear in the plot.

Default: None - Required entry for all plots

<plot> elements of type “slice” can also contain the following attributes or sub-elements. These are not used in “voxel” plots:

basis:

Keyword specifying the plane of the plot for “slice” type plots. Can be one of: “xy”, “xz”, “yz”.

Default: “xy”

background:

Specifies the RGB color of the regions where no OpenMC cell can be found. Should be three integers separated by spaces.

Default: 0 0 0 (black)

color:

Any number of this optional tag may be included in each <plot> element, which can override the default random colors for cells or materials. Each color element must contain id and rgb sub-elements.

id:

Specifies the cell or material unique id for the color specification.

rgb:

Specifies the custom color for the cell or material. Should be 3 integers separated by spaces.

xs:

The attenuation coefficient for volume rendering of color in units of inverse centimeters. Zero corresponds to transparency. Only for plot type “wireframe_raytrace”.

As an example, if your plot is colored by material and you want material 23 to be blue, the corresponding color element would look like:

<color id="23" rgb="0 0 255" />

Default: None

mask:

The special mask sub-element allows for the selective plotting of only user-specified cells or materials. Only one mask element is allowed per plot element, and it must contain as attributes or sub-elements a background masking color and a list of cells or materials to plot:

components:

List of unique id numbers of the cells or materials to plot. Should be any number of integers separated by spaces.

background:

Color to apply to all cells or materials not in the components list of cells or materials to plot. This overrides any color color specifications.

Default: 255 255 255 (white)

show_overlaps:

Indicates whether overlapping regions of different cells are shown.

Default: None

overlap_color:

Specifies the RGB color of overlapping regions of different cells. Does not do anything if show_overlaps is “false” or not specified. Should be 3 integers separated by spaces.

Default: 255 0 0 (red)

meshlines:

The meshlines sub-element allows for plotting the boundaries of a regular mesh on top of a plot. Only one meshlines element is allowed per plot element, and it must contain as attributes or sub-elements a mesh type and a linewidth. Optionally, a color may be specified for the overlay:

meshtype:

The type of the mesh to be plotted. Valid options are “tally”, “entropy”, “ufs”, and “cmfd”. If plotting “tally” meshes, the id of the mesh to plot must be specified with the id sub-element.

id:

A single integer id number for the mesh specified on tallies.xml that should be plotted. This element is only required for meshtype="tally".

linewidth:

A single integer number of pixels of linewidth to specify for the mesh boundaries. Specifying this as 0 indicates that lines will be 1 pixel thick, specifying 1 indicates 3 pixels thick, specifying 2 indicates 5 pixels thick, etc.

color:

Specifies the custom color for the meshlines boundaries. Should be 3 integers separated by whitespace. This element is optional.

Default: 0 0 0 (black)

Default: None

<plot> elements of type “wireframe_raytrace” or “solid_raytrace” can contain the following attributes or sub-elements.

camera_position:

Location in 3D Cartesian space the camera is at.

Default: None - Required for all wireframe_raytrace or solid_raytrace plots

look_at:

Location in 3D Cartesian space the camera is looking at.

Default: None - Required for all wireframe_raytrace or solid_raytrace plots

field_of_view:

The horizontal field of view in degrees. Defaults to roughly the same value as for the human eye.

Default: 70

orthographic_width:

If set to a nonzero value, an orthographic rather than perspective projection for the camera is employed. An orthographic projection puts out parallel rays from the camera of a width prescribed here in the horizontal direction, with the width in the vertical direction decided by the pixel aspect ratio.

Default: 0

<plot> elements of type “solid_raytrace” can contain the following attributes or sub-elements.

opaque_ids:

List of integer IDs of cells or materials to be treated as visible in the plot. Whether the integers are interpreted as cell or material IDs depends on color_by.

Default: None - Required for all phong plots

light_position:

Location in 3D Cartesian space of the light.

Default: Same location as camera_position

diffuse_fraction:

Fraction of light originating from non-directional sources. If set to one, the coloring is not influenced by surface curvature, and no shadows appear. If set to zero, only regions illuminated by the light are not black.

Default: 0.1

<plot> elements of type “wireframe_raytrace” can contain the following attributes or sub-elements.

wireframe_color:

RGB value of the wireframe’s color

Default: 0, 0, 0 (black)

wireframe_thickness:

Integer number of pixels that the wireframe takes up. The value is a radius of the wireframe. Setting to zero removes any wireframing.

Default: 0

wireframe_ids:

Integer IDs of cells or materials of regions to draw wireframes around. Whether the integers are interpreted as cell or material IDs depends on color_by.

Default: None