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{New to CAD] How would I go about parametrically recreating an existing flowing organic shape?

ann_monnann_monn Member Posts: 11
i have a physical hand sculpt, and a .obj file derived from photogrammetry.  i now understand i can neither [import to modify] nor [import as reference object] any polygonal model.  although i have Maya 2010, it can't export parametric models for use in Onshape.  i also now understand i cant import images as reference either.  

the first approach i can come up with is to
   • take physical model onto table saw
   • slice physical model into 1" sections
   • prepare an Onshape workspace with horizontal sketch planes 1" apart, corresponding to physical slices
   • physically trace outlines of each slice onto clear acetate, incorporating center & axis reference marks
   • physically tape the acetate to monitor screen, retrace the corresponding outlines onto each plane
   • use the outlines together with the Loft Tool to arrive at a parametric surface?

how will i ever recreate the subtleties of the sculpt?  Loft does not seem possible to use very expressively.  i can't help noticing the Loft page doesn't speak to strategy; i'd have to blunder around by trial and error like a blind man.  does 

the second approach i can think of is to try to find photogrammetry that yields a parametric model output?  i don't see that anywhere

the third approach is starting over from scratch in a polygonal modeler? but then I'm buying into the catastrophe of Boolean operation errors in a polygonal environment.  rhino looks like a reasonable option, however booleans look catastrophic in rhino -- http://wiki.mcneel.com/rhino/booleanfaq -- you are expected to check all your vertices + edges *individually* and repair them manually

the fourth approach would be just making a big dumb block, and chipping away at it subtractively with blobs.  

it was also suggested i may be able to translate my .obj file into Parasolid or STEP using "a free online translation service".   does anybody here know of such a service?  there are plenty that yield polygonal formats from parametric models, but not the reverse. somebody on reddit is telling me to look at InStep, which will at least output a STEP file, which might possibly be at least visible as a guide surface in OnShape.  

how are other artists modeling expressive, organic shapes, and then modifying them efficiently?

i could buy rhino for $800 with the T-splines add on, and go through the learning curve and use my .obj as a guide to create a parametric version; but it looks like you can only get STEP out of it.  what guarantee do i have that STEP will be usable in Onshape?

i could buy Solidworks for a year for $1200.  pretty steep.  but i see on their forums they have Deform and Freeform Tools, and you can at least import pics as reference

last, how much can i expect to pay to hire someone to replicate this model parametrically: http://imgur.com/3YgJY4C.  ideally just as a surface, because i need to create sizes, and the extrusion would scale with the size, which is undesirable.

thanks in advance for your thoughts




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Best Answers

  • andrew_troupandrew_troup Member, Mentor Posts: 1,584 ✭✭✭✭
    edited November 2015 Answer ✓
    To do what you are trying to do with an MCAD modeller is (as far as anyone can judge without inspecting your "expressive, organic shapes") possible (although not, currently, with Onshape), but it is rather difficult.

    It takes most people years using something like Solidworks to get their skills up to the level where, for really tricky shapes, it is the user dictating the nuances.

    Up till then, there will be times when it is the software deciding whether it feels sufficiently persuaded (and, when it's being bloody minded, inclined) to play ball.

    I think something more towards Modo than Solidworks is probably going to get you where you want to go quicker than most (check out this link:)
    http://www.digitaltutors.com/tutorial/1327-Getting-Started-with-Sculpting-in-MODO#play-33712

    but I wouldn't rule out something like Rhino 

    ON EDIT
    Two things: Onshape DOES now permit import of pictures as a guide for sketching (but I don't see it adding any value to what you're trying to do, at this very early stage in its provision of surface modelling capabilities).

    and the shape you posted (which I missed on first read-through of your post) would be very easy for anyone reasonably well versed in most leading MCAD modellers, but even easier in something like Rhino+Tsplines. If it took them much more than an hour to wrap up, something would be wrong (either with the form in which the information was supplied, or with their level of skill)
  • andrew_troupandrew_troup Member, Mentor Posts: 1,584 ✭✭✭✭
    Answer ✓
    I'm sorry I was unclear: I meant that Rhino + T would be suitable for creating the model.

    Onshape is of no use at present for anything to do with manipulating such a shape.

    If you want to create a parametric surface or solid, it's going to have to be Solidworks or similar.

Answers

  • andrew_troupandrew_troup Member, Mentor Posts: 1,584 ✭✭✭✭
    edited November 2015 Answer ✓
    To do what you are trying to do with an MCAD modeller is (as far as anyone can judge without inspecting your "expressive, organic shapes") possible (although not, currently, with Onshape), but it is rather difficult.

    It takes most people years using something like Solidworks to get their skills up to the level where, for really tricky shapes, it is the user dictating the nuances.

    Up till then, there will be times when it is the software deciding whether it feels sufficiently persuaded (and, when it's being bloody minded, inclined) to play ball.

    I think something more towards Modo than Solidworks is probably going to get you where you want to go quicker than most (check out this link:)
    http://www.digitaltutors.com/tutorial/1327-Getting-Started-with-Sculpting-in-MODO#play-33712

    but I wouldn't rule out something like Rhino 

    ON EDIT
    Two things: Onshape DOES now permit import of pictures as a guide for sketching (but I don't see it adding any value to what you're trying to do, at this very early stage in its provision of surface modelling capabilities).

    and the shape you posted (which I missed on first read-through of your post) would be very easy for anyone reasonably well versed in most leading MCAD modellers, but even easier in something like Rhino+Tsplines. If it took them much more than an hour to wrap up, something would be wrong (either with the form in which the information was supplied, or with their level of skill)
  • ann_monnann_monn Member Posts: 11
    edited November 2015
    thanks very much for the perspective.  i am in such unfamiliar territory.  much appreciated.

    EDIT: clearly, the logical course of action is to hire somebody to recreate model in Rhino.  but, do such models import reliably into Onshape?  and if it imports, will it actually be editable?  how can i protect myself?  would it be reasonable to ask the modeler to start by creating a simple stupid one-minute test-shape, using the same method and tools as for the full recreation, and provide the test-shape in [what format/s?] so i can pre-test the pathway before proceeding with the full task?

    please suggest format/s  =:-)

    in addition, what questions do you recommend i ask prospective Rhino artists to determine their suitability for this task?  



  • kevin_quigleykevin_quigley Member Posts: 306 ✭✭✭
    Honestly? Don't waste your time using any MCAD modeller for "expressive organic shapes" (it would really help to post an image btw). You will not get a "parametric" model unless you rebuild fully in your MCAD app. Using Rhino with TSplines will not give you a parametric model, it will give you a dumb nurbs surface...only editable in Rhino (and then limited).

    The single most important question to ask in CAD is what are you aiming to use the model in? Why do you need a parametric model? Why do you need anything other than Maya? 


  • ann_monnann_monn Member Posts: 11
    edited November 2015
    Honestly? i did post an image!  haha.  it would really help if you click the blue link at the bottom of my post!  =:-)       (quoting you a little bit)

    you guys really contradict each other 
  • navnav Member Posts: 258 ✭✭✭✭
    ann_monn said:
    Honestly? i did post an image! 
    Nicolas Ariza V.
    Indaer -- Aircraft Lifecycle Solutions
  • andrew_troupandrew_troup Member, Mentor Posts: 1,584 ✭✭✭✭
    edited November 2015
    @ann_monn 

    we-e-e-e-ll ..........Technically,      :#       you posted a link, whereas @nav (Nice, helpful non-contradicting, understated guy that he is) went the extra kilometre (he's a metric kinda guy, too) and HE posted an image for you.

    Furthermore, the forum software uses a font so fine, and a blue so dark, that it's hard on many monitors to distinguish a link from text

    That's my excuses, anyway, for missing it on first read-through, and I see I was not alone.....
  • kevin_quigleykevin_quigley Member Posts: 306 ✭✭✭
    Ok my bad, Didn't click the link.

    That would be a 2 min job in Rhino with T Splines...or a 3 min job without. Might be feasible in Onshape but probably not yet. SolidWorks, 4 minute job but fully parametric (and do tell where you can get SW for $1200 a year!).

    Not sure what you mean by us contradicting each other? 

    I'm giving you this advice based on experience of using these tools every day. The form is relatively simply (assuming there is no fine surface detail not showing in the image). When you said organic form I was envisaging something more complex. 
  • ann_monnann_monn Member Posts: 11
    edited November 2015
    i utterly appreciate your time and expertise.  all of you.  i'm new to CAD and i know how much i don't know.  thus, all my questions  =:-)

    i'm happy to hear how simple a task this will be with the right tools in hand!  there's no surface detail

    as i understand it, andrew states that a model created in Rhino using NURBs + T-splines will be editable in Onshape.  kevin states such a model is not.  

    i can't proceed intelligently without knowing the answer

    (i misunderstood "subscription service" to be the full yearly cost of Solidworks standard.  it did seem awfully reasonable, hah)
  • andrew_troupandrew_troup Member, Mentor Posts: 1,584 ✭✭✭✭
    Answer ✓
    I'm sorry I was unclear: I meant that Rhino + T would be suitable for creating the model.

    Onshape is of no use at present for anything to do with manipulating such a shape.

    If you want to create a parametric surface or solid, it's going to have to be Solidworks or similar.
  • ann_monnann_monn Member Posts: 11
    got it.  thanks very much! 
  • kevin_quigleykevin_quigley Member Posts: 306 ✭✭✭
    Ann when you move from any CAD system to another you always lose the native file format editing capability. So whilst I can open a SolidWorks file in Onshape, it comes in as a "dumb solid" - basically just a block of geometry. Depending on the nature of that geometry Onshape (and most other CAD systems these days) can edit the shape.

    For example, if you create a cube in SolidWorks and open it in Onshape, you can resize the cube by moving the faces. You can do the same in SolidWorks. However if you have an organic form like you have it will be next to impossible to edit that shape in Onshape (or indeed most other CAD systems except maybe the VERY expensive ones like NX or CATIA). To make those kind of shape edits you need access to the original model to edit the curves that drive the form.

    SolidWorks (and others) fo indeed have direct freeform face editing and these can be used to edit imported "dumb solids" but often only in very limited ways - but depending on the edits you can scale, flex, freeform edit faces and do things like that. But to be honest the most reliable way to make an edit on a complex surface body is to edit the driving curves and native features - and that requires access to the same application used to create it in the first place.

    What you can do though - in ANY CAD application - is take an imported dumb solid and ADD features to it - such as holes, or fillets and additional details such as shells and ribs (assuming the form allows a shell that is).

    The problem with the CAD industry is that it is driven by superlatives that look great in marketing material but rarely deliver at 2am the night before a 10am presentation!

    One final thing. SolidWorks Subcriptions are not like Onshape subscriptions. With SolidWorks (and most desktop CAD systems) you have to buy a license and then pay a "subscription" to get all the updates and access to online services for the following year. Depending on the package SolidWorks starts at around $4000 in the USA PLUS the subscription cost as an extra. Think that's bad? Here in the UK SolidWorks starts at £4000 and the annual subscription is £1000 (both for the base level package - it is more for the higher level packages). So I think you would need to fork out $5200 to start using SolidWorks.

    My advice would be, define exactly what you need to do, then use the system that delivers as much of that as possible. With your shapes, I would seriously consider using Rhino or SolidThinking. Both are good packages with excellent modelling tools.




  • 3dcad3dcad Member, OS Professional, Mentor Posts: 2,467 PRO
    edited November 2015
    @ann_monn
    If you only need this / few models and your interest in purely on something else than the beauty of modeling things yourself - you are on right track when you try to buy modeling job as a service.

    Modeling is fairly easy if you wan't to get into it, but it takes some time to learn. Knowing how to use tools in the software is easy (just read the help section) the hard part is to come up with right tools for each job. This forum is great source for that.
    //rami
  • ann_monnann_monn Member Posts: 11
    kevin_quigley -- here's what i need to do:

      • [replicate .obj as a surface] << [new to CAD + Onshape, still learning about the options]
      • (surface is the starting point, from which versions are created)
      • resize surface to desired scale as measured in vertical dimension
      • extrude inward [for consistent thickness across all versions]
      • split into 4" h sections using horizontal planar elements using Split Tool
      • using [my existing cutting tool], perforate each section individually using Boolean Tool subtractively
         (http://imgur.com/bABO0Fn -- this is just cylindrical but the setup also tested perfectly on irregular surface)
         (this approach permits custom perf pattern efficiently adaptable to each object)
      • export result for 3D print

    could i perform these steps successfully upon a "dumb surface"?  i will be very happy if the answer is yes.

    i'd like to stay out of Rhino for my boolean modifications, because you are expected to check all your vertices + edges *individually* and repair them manually:  http://wiki.mcneel.com/rhino/booleanfaq --

    i'd like to stay out of Maya 2010 because of its limited system of measurement.  i'd have to build "rulers", a whole system of measuring-blocks maybe?  and i'd have to use another package to resize things to real-world dimensions.  i'm also suspicious it will have the same vertex error issues as Rhino.  

    let me know what you think




  • kevin_quigleykevin_quigley Member Posts: 306 ✭✭✭
    edited November 2015
    One of the best tools in Rhino 5 is the bounding box tool. Select the part, type in the dimensions you want. Boom. Done. We use this every single day. It is a tool that is very common in non MCAD systems. Does Maya have this capability? If so, do your scaling in Maya, export to Onshape and do all the solid edits in that (and I am assuming you are bringing in a surface into Onshape, and that you would be thickening that surface).

    if you can simply scale your surface to get the shape you want then scale it in Maya (it must have a non iform scale tool).

    See here.

    http://download.autodesk.com/global/docs/maya2013/en_us/index.html?url=files/GeomToBBox.htm,topicNumber=d30e81348

    I imagine these apply to your version as well
  • ann_monnann_monn Member Posts: 11
    sadly maya 2010 does not have bounding box dimension capability.  and equally sadly maya 2010 has no exportable format readable in any way by Onshape.

    i think it would be crucial that someone experienced, with access to all the major software tools, create an array of lightweight, simple but known-good files in all formats, so importability and imported-object-functionality could be tested reliably and repeatably.  when i was a dev beta at Discreet, we did this, and created a running spreadsheet of the repeatable outcomes.  for us it was a necessity

    maybe in the CAD world nobody imports files from other applications --?  is it a really outlandish thing to do?  maybe its just not part of the workflow
  • andrew_troupandrew_troup Member, Mentor Posts: 1,584 ✭✭✭✭
    There is a comprehensive list of compatible formats for both import and export, at
    https://cad.onshape.com/help/#export.htm?TocPath=Importing%20%26%20Exporting%20Files|_____0

    The inability to import non-parametric formats from modellers which are  free-form rather than mechanical CAD is perhaps a bit like the early DOS spreadsheets and word processors each being unreceptive to the other's data.

    (Interestingly, though, Apple Macintosh apps did this from day one)

    When MCAD is more of a mature commodity, it is likely to be more amenable to data swaps.
  • kevin_quigleykevin_quigley Member Posts: 306 ✭✭✭
    I think there is an issue here with the term "parametric". Generally in the 3D design and engineering CAD sectors this means "editing via dimensions or feature properties".

    Moving data between apps is an everyday fact in engineering. Apps like Onshape, SolidWorks, Inventor etc are built on modelling kernels. This is where the clever stuff in CAD goes on, at kernel level. As far as the user is concerned apps that use modelling kernels create 'exact' geometry. These systems build surfaces from curves and interpolated surfaces. When these create a bounded form it is a solid. ( I am grossly simplifying this btw).

    Now there are other types of modelling systems that basically use polygons to create the shape...but these are approximations of the exact shape. There are several variants of these, from pure polygonal (3 sides) (like SketchUp) to more complex systems like Modo that use quad meshes and various sub divisional algorithms to define the 'smoothed' surface. These systems are great for doing freeform work where you move faces edges and vertices.

    then you have a new breed of systems that build a sub divisional/polygonal modelling interface to nurbs modelling tools. The best of both worlds, in theory. Look up T splines and Power Surfacing. Or Claydoo. There are others as well...SolidThinking has it built in and Rhino are working on it as well. PTC Creo has it too, as does NX and CATIA.

    So you can import polygonal formats into nurbs systems, and you can get a nurbs surface out, but there are caveats. Generally, the mesh needs to be a quad mesh. Stl tri meshes don't play nicely. Problem is, Onshape doesn't do this yet. I strongly suspect the folks behind Power Surfacing for SolidWorks are working on something though. They sell software components to enable this and loads of companies use them already. So it will come...but at a price probably.

    but even if you do get the mesh format converted to nurbs you need to be able to edit it. With existing TSplines and Power Surfacing add ons for SolidWorks you have basic editing capabilities on converted meshes...like scaling, face edits etc. But if you want real control you need to model from scratch.

    Thererin lies the issue and why users who need to do advanced or complex technical surfacing use applications that can deal with it. SolidWorks has most of the tools needed for this type of work. Onshape does not. Either does Fusion.

    Bottom line is, creating blobby demo jockey surfaces is easy. Creating precision smooth optimised surfaces is hard. Needs a combination of skill and good tools. 

    We admire the skills of a craftsperson who can sculpt wood or metal into beautiful forms, but rarely do we admire the skills of a designer who can create a precise digital model of a complex product. Anyone can do rectangle, extrude, fillet, shell. Not everyone can do 3D curve manipulation and surface creation. If there is one thing I wish CAD vendors would do is be honest about how tough some of this stuff is. Modelling is tough, but creating tools to handle higher end modelling functions is tough too. 

    So, got into a bit of a rant there, sorry! But out here at the sharp end, we have to deal with customer who think we can knock up a production model in minutes thanks to the BS CAD vendors spout about this. 
  • andrew_troupandrew_troup Member, Mentor Posts: 1,584 ✭✭✭✭
    .... out here at the sharp end, we have to deal with customer who think we can knock up a production model in minutes thanks to the BS CAD vendors spout about this. 
    Amen to everything you wrote, and especially this bit!
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