How and why to change scale in 3ds Max?

One of the most common problems in 3ds Max is the unit mismatch of a model. It is very important to understand some of these common mistakes, try to avoid them and remove them from your workflow.

Using correct units will help to create:

• Realistic objects
• Real-life scale
• A better visual experience in the scene
• Seamless integration into other scenes
  

Units Setup

Setting up correct units depends on what country you live in and what type of measurements you use (imperial or metric).

In our case, we are using metric units.

The unit setup dialog will appear when you click from the main menu Customize > Units Setup > System Unit Setup, then select centimeters and click ok.

At the Display Unit Scale select Metric and from the dropdown menu select centimeters.

System vs. Display Units

It is important to understand the difference between System Units and Display Units. Display Units affect only viewport geometry units while System Units determine the actual scale of the geometry. If you import a DXF file (which is unit-less) with one box the size of 1x1x1, after importing it can be 1mm or 1km depending on the System Units. This may have a significant impact on your scene and therefore, it is very important to always set up correct units before importing any models.

Problems resulting from incorrect units

• Zooming and Panning are too fast or slow
• Objects disappear when camera gets close
• Overlapping and flickering polygons
  

Zooming and Panning Are Too Fast or Too Slow

If you’re zooming or panning is way too slow or too fast, the most likely problem is the System Unit Scale. 3ds Max rounds-off floating points when dealing with extremely large or small distances. These round-offs can also cause some other problems like strange viewport clipping or flipped normals. If you work on a tiny scale like seeds of rice, it is recommended to change the System Unit Scale from the default of 1 unit = 1 cm to something like 1 unit = 0.1 cm. For large scale scenes like streets, airports and stadiums, you might increase this value to 1 unit = 10cm or 1 unit = 100cm.

Objects disappear when camera gets close

This situation can happen when you model an object with very small dimensions and have to come very close with a camera or perspective view. This problem is very common in architectural walk-throughs. When a camera gets too close to a wall and you are suddenly able to see through to another room or the other side. This problem is common for designers working with the metric system when you want to use real world metric units and you change the System Unit Scale to 1 unit = 1 meter.

Overlapping and flickering polygons

Overlapping and flickering polygons are usually signs of the wrong scale of your model, but it might happen also  when you work too far from the center of the scene. If you work on an object that is very big, it is recommended to change the units from cm to meters. If you work on a landscape you can change it even to km. You can also face this problem when importing DWG files which usually do not carry information about center on the scene which may result in importing a file too far from the origin.

At the end, if you focus a little bit of time and energy into setting up your units correctly from the beginning and adjusting them when necessary, not only will your workflow stay smooth but your end results will be better.