From its inception in 1988 Okino has long been an active developer and provider of CAD conversion software that has helped to bridge the CAD-world with the non-CAD animation and visual simulation worlds. The following are answers to very common questions posed by our users over the last decade and a half.
Most CAD modelers are BREP “solids” based which define each object by Bodies, Shells and Faces. Faces are one of the basic elements of a solids object. Okino’s CAD importers typically provide you with an option to import the objects “By Body” or “By Face”. Importing “By Body” will create a minimal number of objects in your scene. If these options are disabled (not available for the current import operation) then simply enable the “Optimize Hierarchy” or “Optimize Scene” checkbox that is available on almost all Okino CAD importers – this option was created to reduce the excessive number of “Face” elements. Alternatively, import into the stand-alone PolyTrans or NuGraf software and choose the “Optimize Number of Objects” command from the “Win” menu of the Selector Window’s main menu bar. - Updated: October 19, 2007
Maya v2.51 added the new capability of importing vertex normals for its mesh based objects (these are needed to represent the smoothing of the objects). However, the internal routines inside Maya can become incredibly slow to accept the vertex normals during an import process of large mesh models. Alias has been made aware of this after Maya 3.0 but no improvements have been seen. The solution is to choose the “Create new vertex normals based on angles” radio button on the “Mesh” sub-panel of the PolyTrans-for-Maya “Import Options” panel; this will use smoothing groups instead of the more accurate vertex normals. - Updated: October 19, 2007
3ds max has its origins in the mid-1980’s program called “CAD-3D” written by Tom Hudson on the Atari ST computer. It and other Antic software products were culled together and ultimately became the 3D Studio product line developed by the Yost Group and Autodesk. 3D Studio evolved into 3ds max in the mid 1990’s. Due to this historical evolution of the software, 3ds max still uses the 1980’s concept of “smoothing groups” to represent the smoothing on mesh objects rather than the more ideal, accurate and modern “vertex normals” method. Smoothing groups are just an approximation of the original smoothing information contained in the source CAD model. Smoothing groups have problems representing the original smoothing for CAD objects which share smooth and abrupt angles within the same mesh model and on the same set of triangles. The problems will manifest themselves as “black bands” as well as visible seams along triangle boundaries. In addition, 3ds max has inherently had problems rendering very thin and long “sliver” triangles which are common from data obtained from meshed CAD solids data. Several suggestions are available. First, for the problematic mesh model in question, select it inside 3ds max and apply a “Smooth” object-space modifier to it; enable the “Auto-smooth” and optionally enable the “Prevent Indirect Smoothing” checkboxes. Alternatively, what you need to do is break apart the problematic mesh model so that the parts which are smoothed and the parts which have abrupt angular changes are in two different mesh models; this latter suggestion is rarely, if ever, required to be done. Even though 3ds max uses smoothing groups it still does provide “32 bitmaks” per vertex (internally within its database) and thus provides some good freedom to approximate the original vertex normals of the CAD data with the new smoothing group flags per vertex; this should be compared to Lightwave which only has a single smoothing cut-off angle per-material-per-mesh object and thus has much less freedom to recreate the smoothing properly. - Updated: October 19, 2007
Lightwave needs special attention and instructions in order to properly import CAD models. Lightwave and 3ds max have their origins in the mid-1980’s and both still cling to the usage of approximating “smoothing groups” instead of accurate vertex normals, the latter which is the modern method of representing mesh smoothing. Smoothing groups have the most problems with CAD data where they are a lot of abrupt angular changes within a single mesh object. To compound the problem Lightwave only allows a single smoothing angle to be defined per mesh object which can be very limiting. Due to these facts, you will have to “guess” an appropriate smoothing angle for your data when exporting to Lightwave files via the “Geometry Smoothing Angle” type-in box on the Okino Lightwave exporter. In general, use a smoothing angle between 18 and 30 degrees. After import into Lightwave you can interactively set this smoothing angle with the material editor.
But, there is one case you should be aware of. First of all, each object in the source CAD model becomes one .lwo file on disk, and thus can create a tremendous number of .lwo files. To overcome this situation enable the “Optimize Hierarchy” or “Optimize Scene” checkbox found on most Okino CAD importers; this will heavily reduce the complexity of the scene and create many fewer .lwo files. The only side effect of doing this is that some new "combined" objects may not smooth properly in Lightwave due to the "single smoothing angle per object" (ie: a new combined object might now have a combination of creased and smoothed faces). If this problem occurs then you can either explode those objects based on material assignment inside Lightwave or inside PolyTrans and the problem will go away. - Updated: October 19, 2007
This probably relates to “units matching”. When the person modeled the original scene they implicitly or explicitly chose a “unit of measurement” for measuring sizes in the source modeling program. The imported geometry will have to be scaled in size to match the units of measurement from the source modeling program to the destination program. For example, Microstation files are always measured in millimeters, Maya uses centimeters, Lightwave users meters and 3DS MAX uses inches. Most Okino CAD importers will allow you to specify the desired units of measurement for your destination program which will provide automatic scaling. - Updated: October 19, 2007
Use the “Shrink Wrap” feature inside the Pro/Engineer software. This will create a new assembly and related parts which represent the outer visible surfaces of the original assembly. - Updated: October 19, 2007
Export from your CAD modeling program as “solids” and not “surfaces”. Then, use one of the PTC Granite importers such as ProE, IGES, ACIS, STEP or Parasolids. They will create a mesh based on the BREP (solids) representation of the model. - Updated: October 19, 2007
Okino’s view windows implicitly only show objects up to 1 million units away from the camera to improve z-buffer drawing efficiency (10 million units in more recent versions of the software). We would recommend you update your DXF/DWG importer module (imp_dxf.dll) which will allow you to scale the imported geometry smaller so that the extent of the data is not so large. - Updated: October 19, 2007
The realistic answer is that you need to be reasonable with the size of the source data set. If the data came from a solids modeling program then the data will be in parametric or NURBS geometric format. Once this data gets converted to a mesh representation it will expand by 10 to 100 times in size on average (in terms of memory usage). If the source data is highly curved (like an oil refinery plant with many tubes) then the meshed version of the solids data will become huge. In general if your source data is very large (say, over 200MB of source data) then you just have too much data to start with in the first place – remove excess and useless geometry items in the source modeling program, and use “Shrink Wrap” if you are using Pro/Engineer. There is no definitive answer in terms of “What is too large” but in our experience assemblies up to 200MB in size can generally be imported, optimized and animated adequately in programs such as Maya, 3ds max, XSI and Lightwave. - Updated: October 19, 2007
You need to export your IGES file as a “surfaced model” (128/144/142 entities) with “uv-space trim curves”. If you import the model, press F2 on the keyboard and scroll backwards in the message window then you may find that your IGES file has no “uv-space” trim curves defined in it. Alternatively, import via the PTC Granite IGES importer. - Updated: October 19, 2007
