Modelling question

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 From:  Bloodlust
8220.1 
Hey everyone,

Great to be here. I've got a nooby question thou. MoI seems to be a wonderful program (I came from MODO, but it's unfortunately too slow for me). I know MoI is more NURBS system, but I'll ask either way:
How can I move these selected curves a little bit lower? Move tool doesn't seem to work on particural curves, but only with full outline. Would be great if someone can enlight me!

Thanks in advance!
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 From:  Michael Gibson
8220.2 In reply to 8220.1 
Hi Bloodlust, the NURBS modeling in MoI works very differently than the polygons that you've used in Modo. The curves that you show highlighted there are not just plain curves, they are edge curves which are making up the boundaries of faces. Unlike polygon modeling, in NURBS the edge curves do not define a surface, they just mark which areas of the surface are active and inactive. So you can't manipulate an object by yanking it around by individual edges like you do in polygon modeling.

Polygon modeling is kind of like sculpting where you make objects by pushing and pulling on its point cage in 3D space. NURBS modeling is not like that at all - NURBS modeling is more like drawing where you draw key profile curves, then construct your model from those curves. Some curves are used to create basic stock elements like an extrude or revolve, and others are used to cut away material. NURBS modeling is especially strong in the area of mechanical parts where the design can be defined well by 2D profile curves. If you want to make an organic shape that you want to manipulate by bulging out localized areas of it, that's usually better done in polygon modeling than in NURBS modeling.

The inherent way that polygon models are defined means that you can grab small bits of it and yank them around. The inherent way that NURBS models are defined with an "underlying surface" and then trim curves on that surface means you can't do that but what you get instead is the ability to have a hole in the middle of a surface which is why NURBS modeling is much stronger with cutting and boolean operations than polygons.

Hope this helps!

- Michael
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 From:  Michael Gibson
8220.3 In reply to 8220.1 
Hi Bloodlust, so just to give you more information on your particular shape, in NURBS modeling the way you'd make a dip in your object there would be to draw a 2D profile curve something like this:



Then use Construct > Revolve (turn off the "Cap ends" option in Revolve) to make a type of bulged disc shape from that, this will be a cutting object:



Now take your base extruded object, which you would want to have extruded some extended amount further than what you originally did, and position the disc where you want the top of your final object to be at. Then use Construct > Boolean > Difference to cut the extrusion with the disc:



You will then be left with the imprint of the disc in your extrusion as one combined object:



This is a common thing in NURBS modeling where you will want to construct an extended piece initially and then use a boolean to cut off some excess pieces to form the final shape. Usually you can do the boolean using a 2D curve as the cutting object but in this case you will need to build a revolved surface and use that surface as the cutting object because you don't want just a straight directional cut.

- Michael

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 From:  Bloodlust
8220.4 In reply to 8220.3 
Hey Michael,

Huge thanks for enlightenment. This is my first contact with NURBS because my thinking as rightly noticed is quite different. Thank you again for your help! It's now crystal clear!

Best,
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 From:  Michael Gibson
8220.5 In reply to 8220.4 
No problem! Also there are some tips here for people coming from a poly modeling background, they may be useful:
http://moi3d.com/forum/index.php?webtag=MOI&msg=4865.2

- Michael
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