Tuesday, 17 January 2017

Cooridinate systems in 3d software

If you've ever imported a model into another 3d software application and your model has been 
unceremoniously flipped in another orientation I hope this Dummies guide will help explain why.


Left Handed Coordination


Firstly there are two basic coordinate orientations The Left Handed and the Right Handed system.
The most common by far... is the left handed system.

Thumb "Z" Pointer finger "Y" Middle finger "X"

Right Handed Coordination

Where it gets more complicated is when they start changing the  "Z" and "Y" around and this is where the problems start.

Here are several examples of different "Z" orientations.

You'll also notice they are always coloured R G B as well.

Blender has the "Z" up "Y" depth version
Blender has the "Z" up "Y" depth version




3ds Max has the "Z" up "Y" depth version
Click to see bigger version
3ds Max has the "Z" up "Y" depth version



Fusion 360 has the "Z" Depth and "Y" up version
Click for bigger version

Fusion 360 has the "Z" Depth and "Y" up version



Meshmixer has the "Z" Depth and "Y" up version
Click for larger version

Meshmixer has the "Z" Depth and "Y" up version


Autodesks' Maya also uses the "Z" Depth version and the term Z Depth has more than one meaning.

It is this orientation where we get our calculations for determining how we might set the visual falloff in 3d software where things blur as they are further away from the viewer.

Funnily enough 3ds Max also call this procedure "Z Depth" as well, despite it being in the "Y orientation in Max"



So if you make the "maker coin" in Meshmixer as it is presented in the picture and import it into Fusion it should retain its orientation, but if you import it into Blender or 3ds Max it will probably spin the coin to match its original orientation. This confusingly wont be the case with all software. I made the coin in 3ds Max lying down as you see it in meshmixer, so it hasn't re orientated the coin to suit the program it has reoriented the coordinate system to suit the coin.....

You should find that both Blender and 3ds Max along with some other programs, keep everything as you probably intended and will flip your coin to the orientation you made it in.


Blender

Meshmixer

Fusion360

So if your model is not in the same position you first modelled it in then it is the program you imported into that has a different coordination system to blame.

In Blender and 3ds Max it is very easy to change this orientation. The other programs could also be able to do this but I've never had the need to do this in them.

When exporting in the OBJ format in 3ds Max you get the option to set the "Z" "Y" orientation. This might also be available in other formats like FBX so check before picking your format. Off hand I don't know and I'm too lazy too check :-)

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