You may have experienced it before - the model you see on the screen is divided into many triangular surfaces in different sizes, which together form something similar to the model you expected to see. In such cases, you have a model that consists of polygons. When is it common to use such polygon models, and what can you do with a model of this type in SOLIDWORKS? We will take a closer look at this here.
We take the basics very first; Polygons are a way of representing 3D geometry, which is especially widely used in 3D applications for visual design, film, and VR, such as MODO, Maya, 3Dstudio Max and Cinema4D. One of the advantages of polygon models is that they basically take up little space on disk, and therefore load quickly.
In real-time 3D applications such as games and VR, is this especially important. Polygon models usually make up the basic geometry, and then various image files are added to the models that control not only colors and texture, but also the degree of detail (normal maps), transparent areas (alpha maps) and many other things. Everything for the 3D performance to be as good and realistic as possible. This is a long way from what we are used to in industrial CAD applications, but still polygons have their function in SOLIDWORKS.
Polygon files are used in 3D printing
If you have sent files to be printed on a 3D printer, you may have used the STL file format. This is a polygon-based format that most 3D printers accept. Some types of scanner software also use STL when transferring files to CAD. When you save to STL from a SOLIDWORKS file, a file containing polygons is saved.
If you work a lot with industries that use programs such as MODO and 3DStudio, it is also common to get polygon models from there, although many of these programs can also export to IGES, STEP, ACIS and Parasolid, which are formats that SOLIDWORKS understands better. As in most other similar programs, the geometry in a SOLIDWORKS file is specified as either Boundary Representation (B-Rep) or NURBS, which are other ways of defining 3D geometry, and which are mostly only supported by the typical CAD programs.
Some file formats are displayed as polygons in SOLIDWORKS
If you work in the construction industry and want to have a file in SOLIDWORKS from either Revit or ArchiCAD, it is common to use the IFC format. The IFC format is displayed as polygons and may therefore look a little strange on the screen. If you are going to save to an IFC file or other polygon-based file formats, it is the Image Quality setting I mentioned in the previous section that controls how fine-mesh polygon-mesh will be. Read more about IFC here
You are already working with polygon models
What you see on the screen in SOLIDWORKS when working with a regular model is actually a polygon version of the model. The model you are working on is, in fact, without you noticing it transformed into a polygon version so that the algorithms for shading can reproduce the model on the screen in a lifelike way. You do not really need to consider this polygon model for graphic display, but you will notice it if the resolution of the model is too low for what it is supposed to represent, for example at the ends of long and thin cylinder surfaces.
By the way, you can control this resolution even with the top slider under Document Properties - Image Quality. If you are going to save to a polygon format from SOLIDWORKS, it is this graphic polygon model, with your chosen resolution, that forms the basis for the model that is saved. This is good to know when we look below at how we can import and export polygon models.
How to import polygon models to SOLIDWORKS
SOLIDWORKS can represent geometry in different ways - where the two most common topological categories are Solid bodies and surface bodies. Solids and surfaces can be defined mathematically either as B-Rep or NURBS depending on what the geometry looks like (whether the geometry consists of is prismatic or freeform geometry, for example). Graphics bodies are a third way, and these can be either polygons or point clouds.
SOLIDWORKS can import several different polygon formats, and we distinguish between two different ways of importing these, where one type is available in the Professional and Premium versions and gives you several options for working further with the model.
Import method 1:
With SOLIDWORKS Standard, Professional and Premium, you can import the formats STL, OBJ, OFF, PLY, PLY2 and WRL from the 2017 version. With this method you can choose whether you want to import the model as Graphics Body, Solid Body or Surface Body. You can get the model as solid, but only if it meets the requirements for solid models, for example that the volume must be closed and that the model must be cleaned of so-called non-manifold geometry. The WRL format has its own entry, and the reason for this is that this format has its own import settings, where you can choose whether to include or omit image textures.
Import method 2:
With SOLIDWORKS Professional (2016 and later) and SOLIDWORKS Premium, by activating the ScanTo3D add-in, you can import the 3DS, STL, OBJ, WRL, PLY, PLY2 formats. Select the import option «ScanTo3D Mesh Files….» open the file in such a way that you can continue working with it with ScanTo3D. with ScanTo3D, you can briefly recreate SOLIDWORKS geometry with polygon models as a starting point - which is desirable if the starting point is a scanned product that is to be modified or otherwise included in downstream processes.
How about saving to polygon formats such as OBJ, does it work?
Yes, it's possible. A useful feature of ScanTo3D is that you can also export to multiple polygon formats. The export to STL has its own settings, but what if you want to export to a format that can be opened in 3DStudio, or us say Unity or Unreal environments, to create VR versions of your models? Then you need to be able to export to, for example, the OBJ file format. The workflow for this is:
- First save the SOLIDWORKS file to the WRL file format
- Open the WRL file. With the ScanTo3D add-in enabled, select “ScanTo3D Mesh Files (…) in the file format selector under File - Open.
- If you want to use ScanTo3D to modify the polygon model, you can do it here.
- Export the file to the desired format by selecting for example «ScanTo3D (* .obj)» under the file format selector in Save As.
In other words, it is the Image Quality setting that controls how fine-meshed the polygon model becomes. It must be added that none of the export options give you square polygons (quads), so if the purpose of the OBJ export is to use the model in for example VR, then often the model must be retopologized at the receiver - i.e., rebuilt to optimize performance and prepare for different mappings. Admittedly, there are some programs that can import CAD files where the model is at least experimentally converted to quads.
It must also be mentioned that there is a Free OBJ exporter to SOLIDWORKS. This is a third-party macro that at the time of writing will also work for newer versions of SOLIDWORKS. In addition, there will be various third-party add-ins to SOLIDWORKS that can export to OBJ. I must add that as of today we unfortunately do not sell or have technical support for any of this.
Some precautions for you who want polygon models into a production model
You may sometimes need to insert polygon models into a production file set for the graphic display, or because you have no other substrate than a polygon file. This is entirely possible, but then it's good to know this:
- Polygon models that have very many polygons can reduce the performance of the part or assembly (open, save, rebuild, rotate).
- Polygon models inserted as Graphics Bodies will not be visible on renderings in PhotoView360. The alternative is to use Visualize, which all Photoview-users have access to.
Visualize can also open many different formats, including polygon formats.
So, these are some of the possibilities you have with polygon models in SOLIDWORKS. Feel free to contact us if you want to know more about this.