A Few Simple 3D Modeling Tips
As we explore augmented reality, virtual reality and mixed reality on the HoloLens, we often have a need to create or find 3D models. We have ended up with models from a number of different sources and in a variety of formats. Given all the options available, we wanted to share some of the tools and lessons we have learned.
Converting 3D Models
The first thing to know is that almost any 3D format can be converted into another 3D format. One of the best tools for this turns out to be Blender. Traditionally, Blender is used to create 3D models and animate them, but it can also import a wide range of formats and export in just about as many formats. There is a fairly steep learning curve with Blender, but if you are just using it to convert between formats it isn’t too hard to learn. If you want to put in some extra time, you can use Blender to tweak problems you might find with the imported model as well.
Retaining Model Scale
It can be important to retain the proper scale while converting between different types of models. If you are using Blender the default is going to be a “Blender Unit” but if you want to retain the correct size in the converted output you are going to want to make sure you set Blender to the correct measurement type. For example, we converted a 3D printed model into something we could view in the HoloLens, and the first step was to check what unit the measurements were made in for the original model as shown in the following screenshot from 123D Design:
Here the original unit of measurement was in millimeters.
In Blender you will want to set the units to millimeters before you import. There is a good Youtube video on how to change the setting here. Once you have the model imported, you can view the dimensions to validate that things imported properly:
Next you will want to make sure that when you export the following scale button is toggled as shown or the export will be in “Blender units” instead of the unit you set:
The following image shows the imported model that was originally for the 3D printer sitting next to the physical 3D printed result:
Models In Unity3D
One of the most popular tools for creating VR/AR applications is Unity3D. If you are using Unity3D you may not even have to go through a conversion process at all since it has a long list of formats it supports natively such as .FBX, .dae (Collada), .3DS, .dxf and .obj files as well as Blender files. Some of these formats don’t work as well as others but we have had luck with FBX and Blender formats.
Finding 3D Models
With the knowledge that you can convert between a wide range of different formats, the places you can find existing models is fairly large. For instance there are a lot of 3D printable models that can be found on Thingiverse. Another good source of 3D models is the Sketchup 3D warehouse and if you are using Unity3D it has support for Sketchup as well.
In a future post we will describe a technique for creating your own 3D models out of a set of images. Since that is a fairly complex subject, we will leave it for a post all by itself.
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