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Adding dimensions to an isometric view.

simon_powellsimon_powell Member Posts: 5
Is it possible to show dimensions on isometric views? Onshape allows me to do so and it seems to be in the correct plane, but the dimension stated is smaller than it actually is. My guess is that it's a result of showing a 3D dimension in 2D?

Best Answers

Answers

  • simon_powellsimon_powell Member Posts: 5
    Thanks a lot for the responses! Explained it really well.
  • NeilCookeNeilCooke Moderator, Onshape Employees Posts: 2,347
    Simon - you can also override the dimension and enter the actual value if you need to show the dimension on the isometric. 
    Neil Cooke, Director of Technical Marketing, Onshape Inc.
  • michael3424michael3424 Member Posts: 476 ✭✭✭
    Is there any reason why OS could not calculate and display dimensions on isometric views?
  • 3dcad3dcad Member, OS Professional, Mentor Posts: 2,387 PRO
    I've struggled with this for decades, the best view to show furniture dimensions to people would be single 3d view with all needed dimensions. And the best way to create that view would be 3d cad so that I can easily get new version if dimensions change (ie. not overiding any dimensions).

    Foreshortened values in drawings seems pretty redundant? Does anyone have any use case where this value is needed instead of actual lenght from the 3d model?

    //rami
  • SquidLordSquidLord Member Posts: 15 ✭✭
    3dcad said:
    Foreshortened values in drawings seems pretty redundant? Does anyone have any use case where this value is needed instead of actual lenght from the 3d model?

    It's not the fact that the length calculated for an isometric view is hard. Geometrically it's actually quite simple. The real problem runs thus:

    There is literally no way to tell the difference between an isometric view and an orthographic view on a flat sheet of paper.

    Literally, that is the problem. You cannot tell whether a projection is 3-D or 2-D once it's projected onto a 2-D surface. Take a look at the dowel example. Is that illustrating one dowel laying parallel to the plane of view and the same dowel at an isometric retreating angle or is it illustrating two dowels, one parallel to the plane of view and the other also parallel to the plane of view with a non-orthographic cut across both ends? You can't tell. It is literally impossible to tell.

    That's why the basic assumption in 2-D mechanical drawing is that any part measured is parallel to the 2-D viewing plane. Because without that assumption, you simply cannot understand what you're seeing in any part of the illustration. That has to be a key part of the assessment of said drawings.

    The best way to show furniture dimensions to people is actually an interactive 3-D view with the dimensions hanging out in 3-D. There are a couple of CAD programs which are exporting to an active PDF file which essentially do that, and Fusion 360 allows you to give view access to an online interface to view the model live. Honestly, in Onshape there's no real reason not to give people a link to an assembly derived into its own document if you want to show off a particular piece of furniture with all of its dimensions but without showing all of "your work." It would be nice if we could create a view which actually showed those dimensions attached to the model as it's rotated and moved, and I'd love to see that, but it's definitely not necessary.
  • 3dcad3dcad Member, OS Professional, Mentor Posts: 2,387 PRO
    So I need to forget 2d drawings and hunt for named views with possibility to show certain dimensions - this is something I have requested before we even had 2d drawings in Onshape =)
    //rami
  • brian_bradybrian_brady Member, Developers Posts: 411 EDU
    SquidLord said:
    3dcad said:
    Foreshortened values in drawings seems pretty redundant? Does anyone have any use case where this value is needed instead of actual lenght from the 3d model?

    It's not the fact that the length calculated for an isometric view is hard. Geometrically it's actually quite simple. The real problem runs thus:

    There is literally no way to tell the difference between an isometric view and an orthographic view on a flat sheet of paper.


    I hear you and you are correct, about a drawing on paper. An Onshape drawing is not on paper. OS knows that the view you are asking to connect a dimension to is actually an isometric view and thus should be able to give you isometric dimensions. I would like to see isometric dimensions myself. To make it work, there would probably need to be a new dimension tool. Sometimes the only way to get the isometric dimension you want would be from a surface to a vertex and that is not currently an option.
  • david_weber318david_weber318 Member Posts: 1 EDU
    I have looked at the whole thread here and understand.  I also agree that this has been a problem in all the CAD programs I have used.  I would like to make a formal request a tool/method  to make Isometric Dimensions  possible and easy.  Thanks!
  • erik_bongerserik_bongers Member Posts: 6
    Perhaps this is a standard, and thus has nothing to do with OnShape, but...what on earth could be the use of these foreshortened dimensions?
    Please help me explain these sizes to my carpenter.
    This is mindblowingly weird.
    Wait a minute...when I google "dimensions in isometric drawings", I get loads of examples with REAL dimensions, so...this is just a bug in OnShape?
  • PeteYodisPeteYodis Moderator, Onshape Employees Posts: 300
    @erik_bongers

    No this is not a bug in Onshape drawings.  This is just functionality we have not implemented yet.  We will get to it.  Right now Onshape only places projected dimensions.  This is generally the more popular use case compared to true dimensions.   As others have mentioned there is not an automatic way to know that dimensions should be "true" versus projected.  We will likely include a setting on a view that will set dimensions to be true or projected.  It's likely that isometric views will always be set to True type when we implement this, and then users can switch if they need.  For named views, it will probably be impossible to know if users want true or projected dimensions by default so we will likely default to projected.  We will likely not permit, at first, for views to contain a mix of true and projected dimensions.  That can get awfully confusing to the readers of drawings.  
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