3D Models

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Notable reusable 3d-models

References

The folder 3d-models/Reference contains reference models for model size and rotation. They can be used for orienting and scaling other models. The models have a corresponding prefab in the folder unity/Assets/0Refactored/reusablePrefabs/reference. After they are placed in a scene or prefab and making sure they have a scale factor of 1 and are not rotated, they can be used as a reference for the rotation and size of other models.

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Scaling

Unity works with arbitrary units. The default physics work on the assumption that one unit is one meter. The VR-setup also assumes that one unit is one meter. Therefore all models should be designed in such a way that one unit is equal to one meter.

Here is a checklist for correct model scaling:

• The model was created in life size
• The model is exported to FBX with a scaling factor of one
• It is imported into Unity with a scaling factor of one
• It is placed in a scene with a scaling factor of one
• The model has the correct size for a VR-Player with a scaling factor of one

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Rotation

Unity uses a left-handed coordinate system. Blender uses a right-handed one. Therefore a conversation is needed when importing from Blender to Unity. Models should be created in such a way that they respect the rotation conventions.

Blender rotation convention:

Direction	Color	Interpretation
Positive X	Red	Left
Positive Y	Green	Backwards
Positive Z	Blue	Up

Unity rotation convention:

Direction	Color	Interpretation
Positive X	Red	Right
Positive Y	Green	Up
Positive Z	Blue	Forward

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Origin

The origin of a model should be chosen to make it as easy as possible to place the object in a scene. For example, if the object is a lamp that is mounted to the ceiling the origin should be in the middle of the part of the lamp that touches the ceiling. If the object is a door the origin should be at height 0, forward 0 and in the middle of the width, so that the door can be easily placed to touch the wall and floor.

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Exporting from Blender and importing into Unity

In order to prevent import issues during version upgrades all models should be included via FBX. Blender and other 3d-model files should not be placed inside the unity folder.

Blender steps

• The model is modeled in the correct scale, if not, scale the model accordingly

• The origin of the model is placed in an appropriate spot

• Check if the transform settings are correct (in object mode)

  • The location of the model has to be (0, 0, 0)
  • The rotation has to be (0, 0, 0)
  • The scale has to be (1, 1, 1)
  • If this is not the case use CTRL + A and select All transforms

• The model has to be oriented in along the Y-axis, with the front pointing in the negative Y direction

• The top of the model has to point in the positive Z direction

• Delete all unwanted objects such as cameras or lights, or select only the objects that should be exported

• If the model is a simple model without animations/armatures

  • Open the FBX exporter
  • If the desired objects are selected, select the option Selected Objects
  • Set Apply Scalings to All Local
  • Select the option Apply Transform
  • Export FBX file

• If the model has animations/armatures

  • Rotate the object along the X axis: -90 degrees
  • Use CTRL + A, select Rotation
  • Rotate the object along the X axis: 90 degrees
  • Do not apply the rotation this time
  • Open the FBX exporter
  • If the desired objects are selected, select the option Selected Objects
  • Set Apply Scalings to FBX Units Scale
  • Uncheck Apply Transform
  • Export FBX file

Unity steps

• Import FBX file

A good tutorial is available here:
https://www.immersivelimit.com/tutorials/blender-to-unity-export-correct-scale-rotation

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Note: There is a blender script planned that automates the steps

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