Adding a textured surface to your model’s appearances is one of the best ways to boost the realism of your renderings in SOLIDWORKS. There are two methods for adding surface texture, Bump Mapping and Displacement Mapping. In this post we’re going to compare the two, and go into some detail on what to watch out for when using Displacement Mapping.
Bump and Displace, which is which?
While both Bump Mapping and Displacement Mapping simulate the addition of texture on a surface, they accomplish this in very different ways. Bump Mapping simulates a textured surface by adding shadows and highlights on the surface as they would appear if the texture was really there. This is a quick and easy way of simulating texture that take much less time and resources to render. Displacement Mapping, on the other hand, actually pushes the surface out to create the texture. The shadows and highlights are a rendered as though the model always had the texture.
The biggest difference in the final result generated by these two techniques is found at the edge of the part. Since Bump Mapping only add highlights and shadows, the outline of the part doesn’t change. In the example shown below we can see that the bump mapping hasn’t affected the silhouette of the sphere on the left, this can take away from the realism of the image. With displacement mapping turned on, however, the boundary is pushed up, resulting in a more realistic profile.
Keep in mind that with shallow textures, it’s much harder to tell the difference Bump Mapping and Displacement Mapping. In the images above I presented an extreme example. Try and pick out the Displacement Mapped image below. Not as obvious, is it?
Where Displacement Mapping Stumbles
As we’ve seen above, displacement mapping can produce much nicer results, especially when dealing with pronounced textures. You can run into trouble with Displacement Mapping, however, when you try and add it to more than one surface at a time that are in different orientations. As an example, let’s take the simple shape show below and apply the same dimpled Displacement Mapping texture that we used above.
A good place to start is to use the Projected mapping type projecting down from the top of the part. As we can see below this will create ridges instead of dimples down the vertical face of the part. If this is what you’re after, great! But in this case I would like the dimples to be the same everywhere, so we’ll have to try something else.
Ok so let’s try adding a separate appearance to the vertical faces and the fillet using the spherical projection type instead, shown below.Now the dimples on the vertical surface are much better but there is something weird happening at the interface between the top and side surfaces. Taking a closer look we can see that there is a gap where the dimples don’t quite line up. Keep in mind that it took A LOT of tweaking to make the gap as small as it is in the image below.
One last thing we can try is to add the spherical mapping to the whole part. As shown below, with this method we get a smooth transition along the fillet with no gaps. However, the dimples get smaller and bunch up as they go further up to the top of the part.
So Now What?
In the examples I’ve shown so far, the displacement mapping has been a bit on the extreme side. This was just to help illustrate the problems you can run into. A shallower texture mapping would still run into the same issues, but the gaps created would be smaller.
In the end, the moral of the story is that sometimes there is no perfect solution. In this case you would have to balance what affects the realism of the image most. Ask yourself;
- Is it most important that the dimples are all the same size?
- Could you change the color to something darker to hide the gap created at the interface?
- Is this a main part, taking up a lot of the frame in the final render, or is it just a detail where no one is likely to notice the gap?
- Do I really need displacement mapping in this case, or could I get away with Bump Mapping which won’t make any gaps, since it doesn’t move the surface.
These are all things to consider when you’re applying textures to your models. But in the end, your photo realistic renders will be well worth the effort!