MCNP Options Dialog        

MCNP Options Dialog

Grid Spacing

Except for the Z Increment Item, the Grid Spacing items control the 2D voxel grid overlaying each scan image.

The spacing between the 2D grid lines can be specified in Pixels (recommended) or Centimeters (cm), or inferred from the Number of grid lines to use. The program gives a warning if the settings result in the last grid line lying beyond the edge of the image.

Square Grid

When checked, the same grid spacing is used in the horizontal and vertical directions and the Y (Vertical) field is hidden.

X (Across)

The grid spacing value or number of grid lines used in the horizontal direction.

Y (Vertical)

The grid spacing value or number of grid lines used in the vertical direction. When Square Grid is checked, the field is hidden and the value is taken from the X (Across) field.

Z Increment (Under Development)

The Z Increment determines how many scans in a 3D set are used. Each scan is used if the value is 1. If the value is N > 1, every Nth scan is used.

Grid Style

The items in the Grid Style box affect the display of the voxel grid overlaying an image.

Show Grid

The grid is present when Show Grid is checked. The grid visibility can also be changed with the Show Grid menu items and toolbar button .

Line Width

The thickness of the grid lines, in pixels, can be typed in the edit field or incremented with the arrow buttons. A width of 0 results in a 1 pixel thick line.


The Color button shows the Windows color selection dialog in which the grid line color can be chosen. The current color is shown in the frame to the right of the button.


The generated MCNP geometry can be written as a Lattice or as individual Cells.

When Lattice is chosen, the Cell Combination box is replaced by checkbox items specific to lattices:

Fill Repeat Syntax

When Fill Repeat Syntax is checked, the MCNP R notation is used to condense consecutive fills of the same universe, such as 5 4R instead of 5 5 5 5 5.

List Lattice Fill

When List Lattice Fill is checked, the entire fill specification is shown in the preview window. When not checked, the MCNP commands READ NOECHO and READ ECHO bracket the lattice cell and its fill specification. The cell description and fill extents are shown as commented lines before the suppressed fill.

Coincident Surfaces

The setting affects the positions of the surfaces of the cell containing the geometry when the geometry is written as a Lattice. When checked, the planes of the container cell can be coincident with the lattice planes. When not checked, the container planes are slightly offset towards the center of the model. Coincident surfaces were not allowed in MCNP versi ons prior to MCNP4B; some users have reported problems with their use in later versions.

Cell Combination

When the geometry is written as Cells, a combination algorithm can be invoked to join cells of the same material that share a common boundary. The algorithm may result in a large reduction in the total number of cells where large connected regions of the same material are present.


The combination algorithm is invoked when Combine is checked.

Fast Combine

An alternative fast combination algorithm searches for combination candidates in only one direction in a single pass. The net reduction in cells will not be as much as with the full algorithm but can still be substantial. The alternative algorithm is used if Fast Combine is checked.

Combine in Z

When checked, the algorithm attempts to combine cells in different 2D layers as well as within each layer. Otherwise, the algorithm only operates within each 2D image. Selecting Combine in Z results in longer execution time and may not result in a significant increase in the number of cells combined. Combine in Z is ignored if Fast Combine is checked.

Max. Pass / Terminate

The cell combination algorithm searches through the model in a series of passes. In each pass, a larger number of neighboring cells are included in the search for joining candidates. The transcript window lists the number of cells deleted by combining and (optionally) the time spent in each pass. The sequence of passes ends when the number of passes reaches Max. Pass or the number of cells deleted by combining in one pass is less than Terminate. The Max. Pass limit is ignored if the value is < 0. Terminate must be >= 0.

Mat'l Mix Threshold (%)

The material mixing thresholds are used when defining new materials for cells consisting of multiple materials. The values are entered as a per-cent between 0 and 100. Materials with a voxel cell fraction of less than Ignore are not used in the mixture. If the fractions of each of the remaining materials (after renormalizing to account for any ignore materials) is within Same As of the materials in an existing mixture, that mixture is used. Otherwise, a new mixture is defined.

Edge Material

If the majority of the pixels at the edge of the scan are at or below the minimum pixel intensity shown (or at or above the maximum), the edge algorithm finds all such pixels connected with those at the edge. This material usually represents air or some other medium surround the model. The crop boundary algorithm searches for all pixels forming a connect region with the dominant material at the crop region boundary.

Analyze when Loading

When checked, the edge material algorithm is invoked as each image is loaded. Otherwise, the algorithm must be invoked manually from the Image context menu.

Use Mat'l at Crop Edge

When Use Mat'l at Crop Edge is checked, the crop boundary algorithm is used. Otherwise, the edge algorithm is used.

Threshold (%)

For the edge algorithm, the number of pixels on the edge that are <= the minimum value (or >= the maximum) must be at least Threshold times the total number of pixels on the image boundary in order for the algorithm to proceed. When the crop boundary algorithm is used, the number of pixels at the boundary with the dominant material must be at least Threshold times the total number of pixels on the crop boundary.


The edge material is shown in a separate color unaffected by the current color scheme. The Color button shows the Windows color selection dialog in which the edge color can be chosen. The current color is shown in the frame to the right of the button.


The Frame limits select which frames of a multiframe image are converted. If All is not checked, fields for entering the Start and End frames are present.

Apply puts the changes into effect and dismisses the dialog.

Cancel dismisses the dialog without changing any settings.

Help shows the help page for the dialog.

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