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importing STL


mariocoppola

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Posted (edited) · importing STL
34 minutes ago, mariocoppola said:

Hi all,

do you guys know why cura changes the position of a stl file? I export from Rhino and it is perfectly centrated in the 0,0,0 point, but in Cura it will go in another point of the plate. Why??

 

No why. That is the way Cura works.

 

In most cases Cura simply forgets the absolute position in a stl file. Fortunately, the function Merge Models can restore the relative positions of several models imported from different stl files.

Edited by curasurf
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    Posted · importing STL

    Because STL doesn't define what the 0,0,0 point is with respect to the build plate. There are a lot of models where the point is therefore chosen completely arbitrarily. As such, cura loads the models, places them on the buildplate and then tries to find a spot for them where they fit.

     

    3MF does not have this problem, since it does define where the origin is (it's always in the front left corner of the buildplate). I cant stress this enough; 3MF is a superior file format over STL in every single way.

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    Posted (edited) · importing STL
    1 hour ago, nallath said:

    Because STL doesn't define what the 0,0,0 point is with respect to the build plate.

     

    In my understanding, STL does have a definite 0,0,0 point. I suggest Cura add a button to "restore" the original "postion" and "transformation" of STL models. All the information is there, amd what need to be done is adpating it to the buildplate coordinate system. This would definitely make many new users easier to start their Cura journey.

    Edited by curasurf
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    Posted · importing STL
    21 hours ago, curasurf said:

     

    In my understanding, STL does have a definite 0,0,0 point. I suggest Cura add a button to "restore" the original "postion" and "transformation" of STL models. All the information is there, amd what need to be done is adpating it to the buildplate coordinate system. This would definitely make many new users easier to start their Cura journey.

    It has a 0,0,0 point, but it doesn't define what that point means. Some applications see it as the center, some see it as the left most point of the printer. It also doesn't define what up / down / left / right is. Cura assumes that Z is up, but this is not the case for some CAD software.

     

     

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    Posted (edited) · importing STL
    1 hour ago, nallath said:

    Cura assumes that Z is up, but this is not the case for some CAD software.

     

    Until now, when I use S3D (and many other STL-handing tools) to import STL files exported from some CAD software, I never found the STL models displaced. This seems to mean that for most STL files exported by most CAD softwares, the position and orientation can be handled correctly.

     

    There might be something wrong for STL models exported by 10% (?) CAD softwares. But if it's OK for 90% STL models, it's seems be wortwhile to do something.

    Edited by curasurf
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    Posted · importing STL

    ...well known for Solidworks files.

     

    E.g. look for "The facet normals at https://en.wikipedia.org/wiki/STL_(file_format) or search in Solidworks forum for "facet normal problem".

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    Posted · importing STL

    "...it is perfectly centrated in the 0,0,0 point."  Yes, that is Rhino.  If yours worked then mine would be wrong.

    When I export a 3D solid from AutoCad it must be wholly in the positive octant or it won't export.  It doesn't care where in the octant and no matter where I place it in the CAD software it comes into Cura with the Center of Geometry (the bounding box) at the mid point of the build plate.  Since my STL generator prohibits the origin from being within the model then where is the STL generator putting the origin?  Why would it care where the origin is?  

    I have no idea how many different STL generators are in use, but I would think that none operate exactly the same as others.  When a model comes into Cura WWAAAYYYY over there, I move it.  If I need to have two parts in an exact relation to each other on the build plate then I fool Cura so that when I move both to 0,0,0 they are in the correct relationship.

     

    If a designer wanted to model the ball on the trailer hitch on my truck - the center of the ball is at about X=6100, Y=0, Z=450.  I wouldn't want it to come into Cura at that location.  The left and right door handles are not symmetrical.  The right door handle would come in at Y=1000 and the left door handle at Y=-1000.  My point is that I would still end up moving things around.

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