Encyclopaedia Index

Contents list

Importing CAD Data

Introduction

Allowable Geometries

Converting and Importing Other CAD Format Files

Importing a CAD Object
      Changing units
      Alignment of axes

Assembling a Complete Geometry
     Import by Group

Translation Errors

Introduction

If the geometry already exists as CAD geometry files, a considerable time saving can be achieved through the use of PHOENICS-VR's ability to import CAD files directly.

CAD-packages are frequently used to design engineering equipment. Most have the ability to define their output in a variety of formats. The formats supported directly by VR are:

Many further formats are supported indirectly by translation to .3ds using SimLab Composer from SimLabSoft. This software can be supplied by CHAM and will run silently whenever required once installed. A licence key can be obtained directly from CHAM.

The formats requiring Simlab Composer are:

PHOENICS VR converts the CAD file to the PHOENICS-VR geometry format directly (or indirectly via SimLab) using the Datmaker utility. Once a CAD file is converted to the PHOENICS VR geometry format, its file extension is changed to '.DAT'. In addition, a JPEG thumbnail of the converted geometry is created. This can be used later to import another copy of the same geometry.

The new file is placed in the current working directory by default. Optionally, the new file can instead be placed in a central geometry store, \PHOENICS \D_SATELL \D_OBJECT \FROMCAD.

The local working directory should be used for geometries specific to a single project, or if the user does not have 'write' permission to the central store. The central store should be used for geometries which are to be shared between projects.

Each CAD file should ideally contain the geometry of only one object - as the entire contents of a CAD file are treated as a single VR object, it will not be possible to attach different attributes to different parts of the geometry. If the geometry consists of several objects with different attributes, then one file per object should be created using the CAD system and they can then be converted and imported into PHOENICS-VR individually.

If that is not possible, the import module DatMaker can be used to extract multiple objects from a single CAD or DAT file.

Many CAD and / or DAT files can be imported simultaneously, as explained below. See also the tutorials on importing CAD data.

Allowable Geometries

A few points must be observed prior to generating files which are to be imported into PHOENICS, regardless of what CAD program is used:

• The geometry must be a closed volume. Holes in the surface may lead to detection errors. Datmaker's 'Do hole mend' feature can be used to repair such holes.
• It must be defined by single-sided facets whose normals all point outwards. Inward-facing facets will lead to detection errors. Datmaker's 'Check consistency' feature can be used to ensure all facets point outwards.
• Wirefame geometries cannot be used as they do not define closed volumes.
• Plane geometries for use as PLATE, INLET, OUTLET etc are acceptable provided that they are created and imported as volumes - they can then have one dimension set to zero in VR Editor to make them planar.
• Too many inter-penetrating items within a single file can lead to detection errors - it is best to keep items which penetrate each other as separate objects, or to perform a Boolean join on them (in the CAD program) to create a single item with no internal structures. Datmaker's 'Split into closed volumes' feature can be used to split the CAD file into individual closed volumes, or the 'Split into CAD entities' feature can be used to split into the groupings found in the CAD file, each of which may consist of several closed volumes. These can then be imported as a ' CAD Group'.

At first sight, viewed from above, this geometry looks acceptable:

In fact, it will not work because none of the buildings have bottoms, so they are not closed volumes. This can be seen when viewed from below.

The solver will not detect anything!

Converting and Importing other CAD format files.

SimLab Composer

Installations of PHOENICS created after May 2013 can utilise the Simlab Composer package from Simulation Lab Software Inc - www.simlab-soft.com.

PHOENICS checks if the Simlab Composer is activated and, if available, then uses this utility to convert any files falling outside of the standard list (shown above.) It does this, without the need for user interaction, first into 3DS format and then to the default .DAT format needed by PHOENICS.

The Simlab Composer can be obtained from CHAM. All that is needed is a request to be made to CHAM, which holds a number of Simlab licence strings.

The Simlab Composer can be used in two different ways: 'passive' or 'active'. DatMaker uses Simlab in passive mode for the direct conversion of 3D CAD files into the PHOENICS .DAT geometry format without user interaction.

All the file extensions listed can be converted automatically in this way.

When used in active mode, the user accesses Simlab via the PHOENICS - VR Utilities menu. Simlab can also be used, for example, to create 3D PDF files for emailing results or geometry to customers.

PolyTrans / NuGraf

These third-party programs from Okino Computer Graphics provide a very powerful suite of conversion utilities. They will translate almost any CAD format into almost any other. One of the available export options is STL, so these programs can be used to convert any CAD file into something useable by PHOENICS. The programs have limited capability to modify or repair the CAD model.

AC3D

The AC3D program can import geometries in many 3D file formats including POV-Ray, VRML (1 and 2), RenderMan, 3D Studio 3DS, Lightwave, DXF, Alias triangle, Wavefront OBJ, Direct X, Milkshape, MD2, Quake 3 BSP.

It can perform Boolean operations on multiple objects - for example to join two intersecting objects and leave only the surfaces of the joined part. It can export PHOENICS geometry files, which are directly useable by the VR-Editor.

Importing a Single CAD Object

Locating and Loading the CAD File

CAD geometries are attached to objects just as the CHAM-supplied geometries are. They can be attached to new objects, or to existing objects. The CAD file(s) to be imported can be anywhere on the file system.

There are three ways of importing an existing CAD file:

• In Windows Explorer, select the required CAD file, and with the left mouse button held down drag the file into the VR-Editor window. Release the mouse button to 'drop' the file. Choose whether to create a new object at the origin or replace the geometry of an existing object, then proceed as below (see also VR Editor Object Dialog, Object 'Shape' Page, Drag and Drop; or,
• Click 'Settings',

  

  then 'New', then 'Import CAD Object', then proceed as below; or,

• To start the import process, create a new object, or double-click on an existing object. On the object dialog box, click on to the 'Shape' page then 'CAD File'.

Any of these actions will bring up a dialog box, which allows the type of file to be imported to be selected:

In either case, a file browser will appear, with which the file to be imported can be selected:

A selection of example CAD files is supplied in the folders:

\PHOENICS\D_INTFAC\D_CADPHO\D_STL
\PHOENICS\D_INTFAC\D_DXF

In this example, PIPES.STL has been selected. The CAD file can be located anywhere on the system.

Once 'Open' on the file selection dialog has been clicked, a confirmation of the input and output file names will be shown:

If happy to proceed, click OK, and the selected file will be translated using the DatMaker module. The options for DatMaker are as follows:

• Do Hole Mend: the facets defining the shape of an object should make a complete closed volume. This attempts to identify any missing facets and to fill the resulting hole with new facets.
• Check Folds: sometimes the facets in a geometry may be folded over each other, leading to problems in detection at the solution stage. This attempts to identify such facets and replaces them with unfolded facets.
• Check consistency: the facets making up a closed volume must all face outwards. Sometimes some facets point inwards, again leading to detection problems. This attempts to ensure that all facets point the same way, and that all point outwards.
• No graphic output: when ticked (by default), DatMaker runs silently with no user input. When un-ticked, DatMaker will open a graphics window once conversion is complete allowing the original and converted geometries to be inspected before import to VR-Editor.
• Split CAD file into separate closed volumes: when ticked, each closed volume found in the original CAD will be output as a separate DAT file. This may result in many hundreds of files being created.
• Split CAD file into separate CAD entities: when ticked, each named entity found in the original CAD file will be output as a separate DAT file. Each of these may contain more than one closed volume.

The last two options are mutually exclusive. In either case the names of the output files will be based on the original CAD file name with _1.dat, _2.dat, ... _n.dat added to the end. In addition, a file with a name ending _0.dat will also be created. This file marks the original orign and extent of the single CAD file. It is used as a place holder to ensure the separate files are imported in the correct locations relative to each other.

Note that the more repair processing is selected, the longer the repair may take.

Fitting the CAD Geometry to the Object

Once the translation is complete, the following dialog box will be shown:

This dialog shows how many points and facets were created, and shows the size and origin read from the CAD file. There are then two choices for the size and position:

• Object Size 'Take size from Geometry file'
  • Yes - Take the size of the object from the CAD geometry and resize the object bounding box to fit. If necessary, resize the domain to encompass the object. This is the default
  • No - Scale the geometry so that it fits within the bounding box of the current object.
• Object colour 'Take colour from Geometry file
  • Yes - Take the colours and transparencies of all facets from the geometry file. This is the default.
  • No - the colour of the object will depend on the object type.
• Object origin in PHOENICS domain
  • At object position - the object will be placed at the location of the current object
  • From CAD file - the object will be placed at the location found in the CAD file.
  • User - at a location entered by the user in the Xorg, Yorg & Zorg input boxes, which become active.

Whichever option is chosen, the size and location of the object can be changed as desired later. The domain origin and size will be adjusted if necessary to enclose all objects.

Clicking on 'Reset', 'Fit to Window' on the toolbar will rescale the view to show the entire domain.

If the ' Object constrained by domain' tickbox on the General page is cleared before importing the CAD file or 'Object constrained by domain' is set to No on the dialog, the domain will not be resized if the object becomes bigger than the domain.

Changing Units

The Geometry scaling factor allows the CAD data to be transformed from the CAD units to the units used in PHOENICS-VR. These are normally taken to be meters. Typical scaling factors are:

Note that the units of the CAD origin are always assumed to be meters. If they are not, the correct values must be input otherwise the object may be located incorrectly. When the scale is changed, the Xorg, Yorg and Zorg boxes are updated when 'Apply' is pressed.

Alignment of Axes

It is possible to change the alignment of the CAD and PHOENICS-VR axes. By default, the CAD and PHOENICS-VR axes will be the same. If the CAD geometry was created with, say, the X axis pointing up, but the simulation is to run with Y as up, clicking on the CAD X Y Z align with VR button will cycle the alignments through X Y Z, Y Z X and Z X Y. This will ensure that the dimensions of the object bounding box are set correctly. Further orientation changes within the bounding box can be made by clicking on the Rotate Object Down / Up buttons on the hand-set.

Assembling a Complete Geometry

Import by Group

There are again three ways of importing several CAD (or DAT) files at one time. These are:

• In Windows Explorer, select the required CAD files (which need not all be of the same type), and with the left mouse button held down drag them into the VR-Editor window. Release the mouse button to 'drop' the files, then proceed as below (in this case the list of files will have already been filled with the selected files); or,
• Click 'Settings'

  

  then 'New', then 'Import CAD Group', then proceed as below; or,

• Use the 'Import by group' button on the Object 'Shape' page. Note that this button only appears for a new object.

Any of the above options will display the Group CAD/DAT Import dialog.

The names of the CAD files to be imported are selected with a file browser. The list can contain a mixture of supported CAD data types and also DAT files.

The options for 'Group origin in PHOENICS domain' are:

• At object origin - all objects in the group will be located relative to the position of the current object. This is the default for the first group import.
• Relative to previous - the objects in the current group are located relative to the previous group. This allows several groups of imported objects to be placed correctly relative to each other. This is the default for subsequent group imports.
• User - the origin of the current group is placed at Xorg, Yrg, Zorg which become active.
• From CAD file - the objects are located at the positions in the CAD files.

The Geometry scaling factor and CAD X Y Z alignment buttons are as described above for a single CAD file.

The type and attributes of the first object are copied to all the remaining objects in the list during the importation process. If the objects share many attributes, it is easier to set these for the first object before importing the list.

An alternative is to import each object in the assembly in turn using the 'Take size from geometry file' and 'Take position from geometry file' options, as described above.

Translation Errors

Failure to translate ASCII STL files may be due to the lines ending with Line-feed, rather than Carriage-return+Line-feed. This can be corrected by reading the STL file into WordPad, then saving it. It may be possible to change the output format settings in the CAD system to output a correct file, or to switch to binary format.

Another common error in CAD files is that the normals do not all face outwards. A symptom of this is that the object appears to change shape as the view is rotated, or it appears inside-out. If the setting 'View - Show back of objects' makes the image appear correct, it is a sure sign that some of the normals face in and not out. See the tutorial ' CAD Import / Datmaker: Repairing and Splitting a CAD file into individual objects' for an example.

Although STL formally defines a closed volume, this is not guaranteed. Some STL files may contain holes or gaps between facets. These can lead to detection errors in the Earth solver.

Both types of errors can sometimes be fixed in CAD files using Datmaker, started from Settings - Datmaker operations. The tutorial mentioned above exemplifies the use of Datmaker as part of the process of importing a sequence of STL files.

Contents list