CAD Part: STEP/IGES/SAT

Objects may be imported in either IGES, SAT, or STEP format. These file formats are commonly supported by CAD programs. Imported objects may also be in SAB (native format of Parasolid CAD libraries, see "Imported objects and SAB files"). Once imported, an object may have optical properties such as coatings, glass, and scattering functions applied, and then be ray traced like any other optical component.

To import an object, set the object type to "CAD Part: STEP/IGES/SAT" and select the file name from the drop-down box, or place the file name in the comment column. The file must reside in the <objects>\CAD Files folder (see "Folders" ) and end in the extension IGS, IGES, SAT, STP, STEP, or SAB. The extension must be included with the file name on the comment column.

The following parameters are used by the CAD Part object type.

Parameter # Description Face Name Face #
1 Scale: This dimensionless parameter scales the entire imported solid. Upon import, OpticStudio will automatically attempt to scale the dimensions of the imported solid to match the current dimensions in OpticStudio; this scale factor is applied after that conversion. NA NA
2 Mode: The mode controls the trade off between set-up time and ray tracing speed. Use mode 1 for fast set up time and slower ray tracing, mode 2 for medium set up time and medium ray tracing, and mode 3 for slow set up time and fast ray tracing. Generally use mode 1 during set-up of the analysis, and mode 3 for analysis tracing a large number of rays. NA NA
3-5 # X, Y, Z Voxels: Voxels is a name derived from "volume pixels". A voxel is a 3D rectangle that defines some portion of the total volume occupied by imported solids. Voxel technology allows for fast ray tracing by pre- computing which objects, or portions of objects; lie within a given voxel. A ray entering a voxellated space may only intersect some subset of the total number of voxels; and therefore only these voxels need to be checked for possible ray-object intersections. The greater the number of voxels, the longer the set-up time but the faster the ray tracing. It generally takes some experimenting to determine the optimum number of voxels. Use 5 for all three values if no other values seem obviously superior. NA NA
6-8 Unused. NA NA
9 Explode?: This parameter indicates whether the object has been exploded into its constituent parts (for objects that represent assemblies). Note that manual modification of the "Explode?" parameter does not actually change the behavior of the object. The parameter is there for reference only so OpticStudio knows when to look for the exploded constituent parts already extracted by the appropriate tool and referenced in the editor. The flag is 0 if the object has not been exploded, and is set to 1 if the object has been exploded. Once the flag has been set to 1 by the appropriate tool, there is no way to recombine the object, other than manually deleting the objects corresponding to the constituent parts. To explode an imported object which has not already been exploded, use the tool described in "Explode CAD Part: STEP/IGES/SAT" . NA NA

Imported objects and SAB files

When importing CAD objects from IGES, STEP, or other format files, the data must be translated into the OpticStudio internal object representation. This conversion need only be done once, and thereafter the converted file can be used. This greatly speeds up the loading of imported objects. The converted file name is the original file name with the extension SAB appended. For example, if the original imported file was MyObject.IGS, the SAB file created will be MyObject.IGS.SAB. The name of the file used by the imported object will be changed to the converted file name. OpticStudio will automatically convert imported files to SAB format files if the original file requires more than 2.0 seconds to read and convert, and if the scale factor is 1.0. If the scale factor needs to be something other than 1.0, first set the scale factor to 1.0, then after the file has been converted to SAB format, the scale factor may be adjusted to the desired value. This restriction prevents unexpected scaling of the SAB object when more than one ZMX file is using the same SAB object.

It is recommended that the original CAD file be retained, even though the SAB file will be used by OpticStudio. This allows regeneration of the SAB file should that be required. This feature may be disabled, see "Convert Imported Files To SAB" under "Type tab" .

Comments about imported objects

The advantage to using imported objects is that solids of any shape may be ray traced within OpticStudio. There are no limits on the shape, complexity, or number of objects that may be imported and ray traced. Multiple objects may be imported in a single file. The disadvantage to using imported objects is ray tracing speed, and in some cases, ray tracing accuracy. See the discussion below for important considerations regarding imported objects. An alternative to imported objects exists, see "User Defined Object" .

Ray tracing accuracy for imported objects

Not all types of surface shapes may be ray traced with adequate accuracy using representations supported by CAD file formats, such as IGES, SAT, and STEP. For planes, spheres, and cylinders, the CAD representation, if done correctly, is of very high precision suitable for optical accuracy ray tracing. However, higher order shapes do not usually have a native representation in CAD formats. For example, an aspheric surface with a polynomial term of the form r^16 may have no equivalent representation in the chosen CAD format. A CAD program will generally approximate this shape using a segmented spline, which is in general a piece-wise fit of the surface using multiple lower order polynomials. Typically, multiple third or fourth order polynomials are used to approxi- mate the surface. This is probably adequate for mechanical design, but not for optical precision ray tracing, where surfaces must be know to tiny fractions of the wavelength of light.

This problem often arises when a high optical precision surface is modeled in OpticStudio, then exported as a CAD file, then imported as an CAD file for subsequent ray tracing. The optical precision of the part is lost upon exporting the native OpticStudio asphere as a CAD spline. See "Limitations of exported data" for more information.

For non-imaging optics, the precision of the CAD representation is usually adequate, but for imaging systems, great care must be taken to verify that the imported CAD part is a suitably accurate description of the desired shape. Note OpticStudio uses a relative internal optical precision of about 1E-12 for ray tracing. Most CAD representations of objects are many orders of magnitude more coarse.

Ray tracing speed for imported objects

Simple objects such as spherical lenses typically ray trace slower when imported in CAD format than the native OpticStudio object of identical shape. Ray tracing speed for imported objects is critically dependent upon the efficient representation of the solid shape within the imported file. The identical object may be represented in a nearly infinite number of ways using the various solid and surface entity types supported by the CAD formats OpticStudio can import. For example, an efficient representation of an object may use only a few spline surfaces; while an inefficient representation of the object may use hundreds of smaller spline surfaces. Although from a mechanical modeling perspective the two representations may both be valid and the resulting solids identical, the represen- tation with the larger number of spline surfaces will ray trace dramatically slower. The only remedy is to return to the source of the CAD file and see if a more efficient representation may be generated.

Limitations on imported objects

Not all possible valid CAD format files may be imported, as OpticStudio may only import solids. No lines or surfaces are allowed. Shells must be converted to thin solids before being imported into OpticStudio. Solids must be simply closed with a continuous exterior surface without holes or gaps. No internal surfaces or faces are allowed. Solids composed of multiple solid volumes either in contact or overlapping cannot be ray traced. Multiple volumes not in contact are allowed. Files containing valid solids which do not import may be sent to technical support for review; however no guarantee is offered that OpticStudio can be made to accommodate all possible CAD format entity types and files.

  • Not all possible valid CAD format files may be imported, as OpticStudio may only import solids.

  • No lines or surfaces are allowed.

  • Shells must be converted to thin solids before being imported into OpticStudio.

  • Solids must be simply closed with a continuous exterior surface without holes or gaps.

  • No internal surfaces or faces are allowed.

  • Solids composed of multiple solid volumes either in contact or overlapping cannot be ray traced.

  • Multiple volumes not in contact are allowed.

  • Solids with dimensions larger than approximately 1×104 are not supported by the Parasolid libraries. This can be avoided by changing the lens units. For example change the lens units from millimeters to meters.

  • Files containing valid solids which do not import may be sent to technical support for review; however no guarantee is offered that OpticStudio can be made to accommodate all possible CAD format entity types and files.

Next: