Isosurface Geometry Generator

This tool can be used to generate an isosurface geometry from any 3D mesh tagged with scalar values (eg, a Cartesian weight window mesh used for Monte Carlo particle transport). The tool will create a meshed surface geometry (DAGMC-compliant) using specified isosurface values.

Table of Contents

1. Installation

2. Python Module

3. Command Line Tool

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Installation

Dependencies

• Python 2.7
• VisIt
• MOAB v5.1+ with PyMOAB enabled

Pip install

From the source directory, run the following to install:

  pip install . --user

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Python Module Usage

To use, import the Python module with from IsogeomGenerator import vol.

Steps

To generate a full geometry from a starting Cartesian mesh file, run the following steps in order:

1. Set contour levels values: This will assign the values that will be used for the isosurface selections in the mesh file. The values can be set using one of three methods:

   • assign_levels(levels): User defines the contour levels to be used as the isosurfaces.

     Input: levels, list of floats, list of user-defined values

   • read_levels(levelfile): Read level values from a file. One value per line only.

     Input: levelfile, string, relative path to file with level information.

   • generate_levels(N, minN, maxN, mode='lin'): Auto-generate evenly-spaced level values between the min and max value.

     Input:

     • N: int or float, number of levels (int) to generate ('lin' or 'log' mode); or the ratio (float) to use to separate levels ('ratio' mode).
     • minN: float, minimum level value
     • maxN: float, maximum level value
     • mode (optional): string, options are 'lin' (default), 'log', or 'ratio'.
       • 'lin': N linearly spaced values between minN and maxN
       • 'log': N logarithmically spaced values between minN and maxN
       • ratio: levels that are spaced by a constant ratio N. minN will be used as minimum level value and the maximum level value is less than or equal to maxN.

2. Generate the isovolume database: This step will use the level values assigned in step 1 to create isovolumes in the mesh file using VisIt. Two consecutive level values are used to generate an isovolume in the meshfile and the surface of that volume is exported as a meshed surface. Each isovolume is exported as one file in the database.

   • generate_volumes(self, filename, data, dbname='/tmp/'): Creates an STL file for each isovolume. Files are generated in the dbname folder.

     Input:

     • filename: string, path to vtk file with the mesh file
     • data: string, name of the data whose values exist on the mesh (will be used to generate the isovolumes)
     • dbname: (optional), string, Absolute path to the folder to store created surface files. Default: a folder called tmp/ in the current directory.

3. Create the DAGMC isosurface geometry:

   • create_geometry(tag_for_viz=False, norm=1.0, merge_tol=1e-5, dbname='/tmp/', tags=None, sname=None, sdir=None): Creates a DAGMC-compliant isosurface geometry from the isovolume files in the database created in step 2 using MOAB.

     Input:

     • tag_for_viz: bool (optional), True to tag each triangle on every surface with the data value. Needed to visualize values in VisIt. Default=False.
     • norm: float (optional), default=1. All data values will be multiplied by the normalization factor.
     • merge_tol: float (option), default=1e-5 cm. Merge tolerance for mesh based merge of coincident surfaces.
     • dbname: string (optional), name of folder to store created surface files. Must be absolute path. default: a folder called 'tmp' in the current directory
     • tags: dict (optional), set of names and values to tag on the geometry root set. Dictionary should be structured with each key as a tag name (str) and with a single value (float) for the tag. Example: {'NAME1':1.0, 'NAME2': 2.0}
     • sname: string (optional), name of file (including extension) for the written geometry file. Acceptable file types are VTK and H5M. Default name: isogeom.h5m

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Command Line Tool

The steps for creating an isosurface geometry can be done on the command line with the generate_isogeom command. This tool can be run in three different modes:

• full: this will run both the visit step then the moab step (described below). Command:

  generate_isogeom full <meshfile> <dataname> [options]
  

• visit: starting from a Cartesian mesh file, this will generate only a database of separate isosurface files from VisIt (step 2 above). Command:

  generate_isogeom visit <meshfile> <dataname> [options]
  

• moab: this will start from the database (generated in the visit step) to create a DAGMC-compliant isosurface geometry using PyMOAB (step 3 above). Command:

  generate_isogeom moab [options]
  

To view the three different modes, run generate_isogeom --help.

Options

Each mode has different required or optional arguments needed at run time. Below is a table summary of those options. This information is also available via terminal help message: (generate_isogeom [mode] --help).

• X = required
• O = optional
• - = Not allowed

Command Option				Run Mode
	Option	Description	Default value	full	visit	moab
Mesh file information
Cartesian Mesh File	meshfile	Relative path to the Cartesian mesh file that will be used to generate isosurfaces.		X	X	-
Data Name	dataname	The name of the scalar data on the Cartesian mesh file to use for the isosurfaces.		X	X	-
Level value information	One of the following options is required: -lf, -lv, -gl	These options set the values that will be used for the isosurfaces in the mesh file.		X	X	X
Level File	-lf/--levelfile LEVELFILE	Relative path to file containing values to use for isosurface levels. File should be structured to have one value per line.		O	O	O
Level Values	-lv/--levelvalues VAL [VAL VAL]	List of values used to generate isosurfaces in VisIt.		O	O	O
Generate Levels	-gl/--generatelevels ratio/log/lin	Specifies the mode for generating level values to be used for the isosurfaces. If used, values for the minimum and maximum levels (-lx) and the ratio or number of levels (-N) are also required. Options are: (1) ratio: N is the ratio between levels ranging from the min value up to, but not exceeding, the max value. (2) log: N is the number of levels to be evenly spaced logarithmically between the min and max values. (3) lin: N is the number of levels to be evenly spaced linearly between the min and max values.		O	O	-
Number of Levels	-N/--numlevels N	(Required if using -gl, otherwise not allowed)		X/-	X/-	-
Level Min/Max	-lx/--levelextrema MIN_VAL MAX_VAL	(Required if using -gl, otherwise not allowed)		X/-	X/-	-
Geometry information		These options specify information needed to generate a DAGMC geometry from the isosurfaces produced from VisIt.
Database Path	-db/--database DATABASE_PATH	Relative path to folder where isosurface meshfiles from VisIt are to be saved (visit step) or read from (moab step).	A folder called tmp/ in the current directory: ${PWD}/tmp/	O	O	O
Mesh-based Merge Tolerance	-m/--mergetol TOL	Merge tolerance for mesh based merging of coincident surfaces.	1e-5	O	-	O
Surface Normalization Factor	-n/--norm NORM_FACTOR	All level values will be multiplied by this normalization factor when the geometry is generated.	1.0	O	-	O
Visualization Tag	-v/--viz	If set, surfaces generated will be tagged with data for visualization purposes in VisIt. Note: this will increase the file size as each individual facet will be tagged with data.		O	-	O
Isosurface Geometry Filename	-g/--geomfile GEOM_FILENAME	Filename to write generated isosurface geometry file. Must be either a .h5m or .vtk file name.	isogeom.h5m	O	-	O
Save Location	-sp/--savepath PATH	Absolue path to folder to write generated geometry file.	Database Path	O	-	O
Extra Tag Information	-t/--tag TAGNAME TAGVAL	Information to tag on the whole geometry. First entry must be the name for the tag (string). Second entry must be the value for the tag (will be tagged as float). Option can be set more than once to set more tags.		O	-	O

Example Usage

All of these examples will assume a starting Cartesian mesh file called cw_mesh with the desired data called wwn.

• Run all the steps start to finish, defining 3 values for the level information at runtime, and tag for visualization:

  generate_isogeom full cw_mesh wwn -lv 0.1 5.2 12.3 --viz
  

• Generate a geometry start to finish, with 5 levels logarithmically spaced from 1e-5 to 1e+3. Also tag the geometry two metadata tags called E1 and E2 with values of 1.0 and 10.0, respectively:

  generate_isogeom full cw_mesh wwn -gl log -lx 1e-5 1e+3 -N 5 -t E1 1.0 -t E2 10.0
  

• Generate only the isovolume database using levels that logarithmically spaced between 0.1 and 1e+14 and specifying where to write the generated database:

  generate_isogeom visit cw_mesh wwn -gl log -lx 0.1 1e+14 -db my_database/
  

• Generate an isovolume database in the default location using levels between 1.0 2e+4 that are spaced with a ratio of 20:

  generate_isogeom visit cw_mesh wwn -gl ratio -lx 1.0 2.e4 -N 20
  

• Generate an isosurface geometry using the levelfile and database located in my_database/, specifying a file name for file produced:

  generate_isogeom moab -lf my_database/levelfile -db my_database -g geom1.h5m
  

• Generate a geometry from a database located in my_isogeom/, read the level info from a file called levelinfo, mutliply all data by a factor of 2e4, and save the file as my_isogeom.vtk in a new folder called output_folder/:

  generate_isogeom moab -db my_isogeom/ -lf levelinfo -n 2e4 -g my_isogeom.vtk -sp output_folder/