Working with Purchased Models

There are many asset stores popping up online like 3D Ocean, Turbosquid, CGPeopleNetwork (was 3D02.com) that makes life and timelines easier by purchasing assets. I won’t go into licensing issues but rather this article is to give you a real world case example of dealing with a purchased asset and what that might mean to your schedule or planning.

We assume that by purchasing assets means receiving a quality product. Most would assume, as “common sense” might persuade, a vendor selling digital assets as a service between you and the producer would review and offer or rate product quality. Without giving a review of the available vendors I will instead advise you to thoroughly read a vendor’s terms and services especially relating to quality and complaint resolution practices.

I can attest that I have, more often than not, run into quality issues with products with issues from sloppy meshes to missing textures to horrid UV maps. So when purchasing assets be sure to invest a budget of contingency for model clean up and tweaking.

First Step: Interrogation

My example case comes from a Galaxy S3 phone model purchased. The site claimed to  have the model prepared for Cinema 4D with materials and textures. At first glance the model appeared usable but after a more thorough investigation I found issues that required repair and optimizing.

The first area to interrogate is the model mesh quality and  mesh topology. I was surprised the model was triangulated rather than a quadrangle (4-sided) polygon mesh. However, if you inspect the mesh you can see the original mesh probably was modeled in “quads” but to provide this model in a “native” Cinema 4D format the supplier decided to convert the model; resulting in a triangulated mesh.

Looking at the product in shaded mode, you should immediately see issues. Upon seeing mesh errors, I then test the mesh since the artifacts shown below are indications of unwelded vertices.

Galaxy S3 Shading Errors

To test the mesh I used a smoothing tool (Iron tool in Cinema 4D) and low and behold we see indeed the mesh is not contiguous which resulted in tearing of the model producing gaps:

Click for Larger

Click for Larger

Looking at the image above, you can see the highlighted areas above this model is in need of some repair; it won’t hold up to high quality rendering. You will want to continue this review for other important parts in the model to understand where the model is flawed.

Another area to review is the model resolution for the intent you require. The model in question was suspect in key areas like the output jack:

Click for Larger Image

Click for Larger Image

Step Two: Repair Model

Repairing the gross errors in the tearing mesh is relatively easy. The tearing and stippling is a result of duplicate vertices not being joined resulting in mulitple patches. Any modeling program with have a “merge vertices” type function and in my example using Cinema 4D I use the Optimize command. Using Optimize, I merge vertices and remove orphaned vertices (unused vertices) which results in a smooth appearing mesh:

Click for Larger Image

Click for Larger Image

It is worth noting that this operation does not smooth the mesh physically but rather allows the mesh smooth shading to work properly. In fact simply subdividing a mesh will not create additional smoothing and I will cover this more in the optimization section which move onto after ensuring our models do not suffer from unmerged vertices.

Step Three: Optimizing the Model

Prior to optimizing the mesh of your model, it is worth taking a second to mention Phong Angle and Vertex Normals. In a very simple set of term, the Phong Angle controls the visual smoothing of polygons by average angle between polygons. Whereas vertex normals are used to more accurately provide smoothing information.

The difference between phong angle smoothing and vertex normal smoothing is important because the optimizations I will be mentioning change the mesh which will compatible only with smoothing done by phong angle control. If you edit a mesh where its visual smoothing is determined by vertex normals you will destroy the information and then be left with shading errors. In some cases, your program may have methods to re-interpolate vertex normals to approximate the changes. To proceed be sure your model smoothing is being done by phong angle control.

I wrote earlier that the purchased model of the Galaxy S3 was triangulated and I also made the statement that it appeared the modeler used a quad topology method. To illustrate review the image below where I have highlighted polygon “loop” topology generally observed when modeling with quads:

Illustrating Loops in Triangulated Mesh

Illustrating Loops in Triangulated Mesh

Recognizing this is very important because it means we can employ some mesh tools to revert back to relatively quad based mesh. Having a quad based mesh means we can then employ subdivision surface smooth using tools like Turbosmooth in 3DS Max or HyperNURBS in Cinema 4D. You could attempt to do so with the triangulated mesh but the results are typically not predictable. Also, you cannot apply subdivision smoothing to meshes controlled by vertex normals.

Below is the result of using the Untriangulate function in Cinema 4D where I applied the function to the back cover only. A good starting point is using a similar angle value driving the phong angle; a value too low will result in poor results.

Galaxy S3 Cover Untriangulated

So far this is looking promising. We could apply subdivision smoothing to get a high definition mesh for closeups. However, all is not rosy because this is but one part in our model. Let’s look at another part to see what it might mean to not be so lucky.

Galaxy S3 Glass Click for Larger Image

Click for Larger Image

Click to Larger Image

 

 

By using standard modeling tools we can remove the offending edges and repair the mesh to use a clean quad topology.

Galaxy S3 Glass Mesh Cleanup

Step Four: Improving Mesh Resolution

The final step is to improve areas of the model that require better resolution for close up rendering. Let’s go back and review the issue where we saw facets on the output jack of the phone. The images below show the transition from triangulated mesh to the a smoothed mesh. Beginning with the original mesh, we use the untriangulate command to produce a quad mesh. With a clean quad topology we can apply a subdivision surface smoothing generator; in Cinema 4D I am using a HyperNURBS which allows us to add different levels of smoothing.

Screenshot_2013-01-09_23_13 Galaxy S3 Back Cover Mesh Optimized Screenshot_2013-01-09_23_23

 

Summary

We covered at length the pitfalls and considerations when attempting to use purchased model assets.

  1. Interrogate the model. Use viewport shading (without lines) to look for stippling and odd shading errors. In areas where there is errors test the mesh using modeling tools such as smoothing tool or brush tool to see if vertices are not merged.
  2. Optimize the model. Some models can be triangulated due to model conversion and to maximize efficiency of the model we want to have as clean mesh as possible. Using untriangulate functions will allow quad generation and if desired ngon creation.
  3. Review the optimization and clean up erroneous edges and complete broken topology loops.
  4. Focus on areas where improved smoothing is required. Improving the quadrangle mesh and cleaning up mesh loops will allow using a subdivision mesh smoothing generator to now improve rendering detail.

 

 

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