Author Topic: Imported model scale is always way off  (Read 323 times)

jonnyquest

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Imported model scale is always way off
« on: October 24, 2017, 01:07:25 AM »
Meshmixer is always defaulted in MM for me. Can't figure out how to make default inches.

Obj, or stl files types end up being 2mm big when they should be around 6in.

Why doesn't my model size stay the same when I import it?


MagWeb

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Re: Imported model scale is always way off
« Reply #1 on: October 24, 2017, 04:31:42 AM »
.Obj and .Stl do not know Units. These formats only know pure values.
So if you save an object (e.g. the default bunny which is 50 in Y) only "50" is stored no matter if you export from 50 mm, 50 cm, 50 m, 50 ft or 50 inch.

In MM "mm" is the default unit (unfortunately no way to change that). Anytime you import an object to a fresh (or replacing the existing) scene MM will fall back to "mm".
Now the first thing you need to do is to go to ANALYSIS/UnitsDimension and set inches there. If your file was written from a scene using inches you need to keep XYZ the same while you need to convert it if it was written using "mm" (or any other unit).
If your scene is using inches now and you import another file (written in in inches) appending it to the scene it should show up scaled right.
A problem are mixed source where different files were written in different units....

Against that MM's own format .MIX saves the scene including the used unit. So as long as you deal with MM use .mix format
I'm just a user as you are. Being no Autodesk employee: I do not know where this road will lead to, nor do I claim to've all stuff got right.

jonnyquest

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Re: Imported model scale is always way off
« Reply #2 on: October 24, 2017, 04:43:48 PM »
So what's the best way to bring MM modified mesh back into Rhino? I'm using this drawing to CNC the part. Exact size and location is imperative to my fixture.

MagWeb

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Re: Imported model scale is always way off
« Reply #3 on: October 24, 2017, 05:50:01 PM »
If you export from Rhino (at inch) to mesh > import to MM > export from MM to mesh > import to Rhino (at inch) you may not worry about units for, as said, values stay the same as long as you do no conversion.
Ignore the "mm" unit labels in MM and think of them as inches (or set UnitsDimension to use inch labels while keeping the values the same).

Note : Here on Rhino for Mac there's a import dialog where one can set the imported mesh's unit. If this unit is different to Rhino's scene ("model") unit, Rhino  does a auto conversion (scaling). So if you're sure that your mesh already owns the right values, you've to set the same unit here as your Rhino scene uses.
I'm just a user as you are. Being no Autodesk employee: I do not know where this road will lead to, nor do I claim to've all stuff got right.

jonnyquest

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Re: Imported model scale is always way off
« Reply #4 on: November 04, 2017, 05:10:03 PM »
Just a follow up, when I export back into Rhino, no issues! My geometry is correct.

Thank you very much!

Adisanut

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Re: Imported model scale is always way off
« Reply #5 on: November 22, 2017, 09:35:57 PM »
I'm the same with you. I modified the structure size. It felt like it was the same.