Model orientation

Several times over the last few years I have received models from people which were modelled orthogonally. When I asked them to properly orient the building they said that that was not possible in their software (read not Autodesk) and that I had to rotate it in Navisworks. 

First of all it’s my opinion that anyone supplying a model has to take care of getting it at the right position and at the right orientation. Because any rounding errors will throw of the clash detection. If everyone would make the same mistake it wouldn’t be a problem but if some get it right and others don’t, than we are in a world of hurt.

Imagine the following conversation at the building site… You wouldn’t accept it there either.


Model like you are going to build!

Model orientation

10 thoughts on “Model orientation

  • 2015-09-11 at 19:33
    Permalink

    Most cad software can not handle a 0,0,0 very far from any modeled object. For example there is s 20 mile limit in revit (it used to be a 2 mile limit). There are other limits in other software, autocad included. And in more advanced 3d-cad, used for detailed modeling (LOD 400), like Tekla, the model has to be closer to 0,0,0, than if software which generates not that detailed models, like Revit, are used.
    And exactly what happens the rotating the model depends on the chosen precision in the software, so when the models are rotated in different cad programs, in some situations they do not end up in the exact same place.
    There for best practice is to use a project coordinate system close to the building modeled, an orthogonal to the building one.
    The surveyor or who ever needs transformed coordinates has to handle that them selves, using software in which it can be done correctly. This is not work for what ever architect or other drafter, you at least have to be aware of the problem with precision that can arise to be able to avoid them.

    Reply
  • 2015-09-11 at 19:33
    Permalink

    Most cad software can not handle a 0,0,0 very far from any modeled object. For example there is s 20 mile limit in revit (it used to be a 2 mile limit). There are other limits in other software, autocad included. And in more advanced 3d-cad, used for detailed modeling (LOD 400), like Tekla, the model has to be closer to 0,0,0, than if software which generates not that detailed models, like Revit, are used.
    And exactly what happens the rotating the model depends on the chosen precision in the software, so when the models are rotated in different cad programs, in some situations they do not end up in the exact same place.
    There for best practice is to use a project coordinate system close to the building modeled, an orthogonal to the building one.
    The surveyor or who ever needs transformed coordinates has to handle that them selves, using software in which it can be done correctly. This is not work for what ever architect or other drafter, you at least have to be aware of the problem with precision that can arise to be able to avoid them.

    Reply
  • 2015-09-11 at 19:59
    Permalink

    Thank you Anders,

    I am quite aware of the issues between different precisions of different programs. Due to mathematics every program becomes less precise the further away you move from it's 0,0,0. The problem I want to point is that the person who does the clash detection is not the person who should move models from different software packages to the right coordinates and the right orientation. When I can have my way I also send back Revit models that have not been properly setup.

    Regarding your system you describe, I am sure it works but why can't we model the way we build. It's strange and I think it's even an old heritage from the time we drew on paper.

    Another point, not mention before, is that certain analysis do not produce the correct results if the model is not correctly oriented.

    Regarding Tekla, and I don't know much about Tekla, I wonder why don't they just work the way they want but once they need to export, then you position and orient the export to the right location and orientation (in the export itself). This way the responsibility remains with the modeller.

    By the way what you describe with project coordinates is exactly how I work in Revit 🙂

    Thank you very much for the time to share your insights it's most appreciated.

    Reply
  • 2015-09-11 at 19:59
    Permalink

    Thank you Anders,

    I am quite aware of the issues between different precisions of different programs. Due to mathematics every program becomes less precise the further away you move from it's 0,0,0. The problem I want to point is that the person who does the clash detection is not the person who should move models from different software packages to the right coordinates and the right orientation. When I can have my way I also send back Revit models that have not been properly setup.

    Regarding your system you describe, I am sure it works but why can't we model the way we build. It's strange and I think it's even an old heritage from the time we drew on paper.

    Another point, not mention before, is that certain analysis do not produce the correct results if the model is not correctly oriented.

    Regarding Tekla, and I don't know much about Tekla, I wonder why don't they just work the way they want but once they need to export, then you position and orient the export to the right location and orientation (in the export itself). This way the responsibility remains with the modeller.

    By the way what you describe with project coordinates is exactly how I work in Revit 🙂

    Thank you very much for the time to share your insights it's most appreciated.

    Reply
  • 2015-09-12 at 20:28
    Permalink

    This is why shared coordinates exist. The Revit model can be located near the origin of the file while it references a coordinate system that is very different. All anyone needs to do to resolve this link a survey, position it properly and use Acquire Coordinates. I prefer to create a Revit model for site and link the survey into that. Then I link the building to the site, mimicking reality…position the building properly and then Publish Coordinates. This way the model can be orthogonal, easy to describe on drawings AND related to the site position properly.

    Reply
  • 2015-09-12 at 20:28
    Permalink

    This is why shared coordinates exist. The Revit model can be located near the origin of the file while it references a coordinate system that is very different. All anyone needs to do to resolve this link a survey, position it properly and use Acquire Coordinates. I prefer to create a Revit model for site and link the survey into that. Then I link the building to the site, mimicking reality…position the building properly and then Publish Coordinates. This way the model can be orthogonal, easy to describe on drawings AND related to the site position properly.

    Reply
  • 2015-09-12 at 20:28
    Permalink

    You can do as you describe when exporting from Tekla. But if the model is moved to far from 0,0,0, the export will be messed up, since the precision will be to bad. I don't think you can move it as far away as a revit model since it is a more detailed model. And high precision is as most important when rotating the model.
    But the simplest way to handle the problem with the precision, which we will have to live with, is to use a project coordinate system with 0,0,0 close to the building modeled, and oriented after the building.
    And leave transformations and such to surveyors. The problem will probably only be worse in the future when the models will be more and more detailed.

    Reply
  • 2015-09-12 at 20:28
    Permalink

    You can do as you describe when exporting from Tekla. But if the model is moved to far from 0,0,0, the export will be messed up, since the precision will be to bad. I don't think you can move it as far away as a revit model since it is a more detailed model. And high precision is as most important when rotating the model.
    But the simplest way to handle the problem with the precision, which we will have to live with, is to use a project coordinate system with 0,0,0 close to the building modeled, and oriented after the building.
    And leave transformations and such to surveyors. The problem will probably only be worse in the future when the models will be more and more detailed.

    Reply
  • 2015-11-23 at 11:52
    Permalink

    @Steve, that's what I do too. Basically my project base point stays on the revit origin so I can always link in origin to origin if needed. I never rotate my models to draw orthogonally. I prefer scope boxes.

    @Anders, it's the rotation that worries me the most. I have seen quite some things going wrong due to rounding errors

    Reply
  • 2015-11-23 at 11:52
    Permalink

    @Steve, that's what I do too. Basically my project base point stays on the revit origin so I can always link in origin to origin if needed. I never rotate my models to draw orthogonally. I prefer scope boxes.

    @Anders, it's the rotation that worries me the most. I have seen quite some things going wrong due to rounding errors

    Reply

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