Rhino "how to" question

Discussion in 'Software' started by TheFisher, Jan 22, 2004.

  1. TheFisher
    Joined: Oct 2003
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    Location: Middleburg, FL

    TheFisher Junior Member

    How do I go from a table of offsets to entering the data into Rhino?
     
  2. duluthboats
    Joined: Mar 2002
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    Location: Minneapolis,MN, USA

    duluthboats Senior Dreamer

    The short version is to enter each station as a series of points. Select single point from the curve menu. The command line will ask for the coordinates, enter, X comma, Y comma Z, return. Then use curve, polyline from points, to connect the points. Then loft a surface from the curves. It should be this easy but in reality it isn’t. I wish I had the skill to write a good tutorial on this subject. My advice is to do all the Rhino tutorials and learn how all the tools work before you try drawing a hull from offsets. It is much easier to draw a hull from scratch. When you get frustrated take a break and come back to it later.

    Good luck
    Gary :D
     
  3. nico
    Joined: Jan 2003
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    nico Senior Member

    or learn how to make scripts it is much faster for entering points
     
  4. SailDesign
    Joined: Jan 2003
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    SailDesign Old Phart! Stay upwind..

    "or learn how to make scripts it is much faster for entering points"

    Geek! :)
     
  5. duluthboats
    Joined: Mar 2002
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    Location: Minneapolis,MN, USA

    duluthboats Senior Dreamer

    LOL!! That was close to my thought as well. But I would like to learn this trick, so maybe Nico could give a little tut on scripting a table of offsets into Rhino. I’m not too proud to beg. PLEASE!!

    Gary :D
     
  6. Polarity
    Joined: Dec 2001
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    Polarity Senior Member

  7. mee
    Joined: Oct 2003
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    Location: Ajax, Ontario, Canada

    mee New Member

    Table of offsets to 3D model

    A number of programs will import x,y,z coordinate values directly into a CADD drawing such as Rhino or AutoCAD. I have been experimenting with this process and have successfully generated coordinate sets (i.e. x,y,z values)
    from tables-of-offsets. The station gives the x value, the offset from the centre-line if the boat will give the y value and the z value is generated from the distance above an arbitrary baseline or waterline reference. Each section of the boat can be "built" by inputting 8 - 15 points that describe the section shape. This is the easy stuff! It can be prepared as a simple ASCII or text file by using a spreadsheet such MS excel and then saved as a "text only" file. The format really isn't too difficult or rigid; it can be comma or space delimited, contain a point number for each set of coordinates and also contain a description. For example,

    10 345.78 234.56 67.78 Deck

    is a typical listing for a single point on the surface of he boat. The order for the information really isn't too important as long long as you know what is what.

    10 = point number
    345.78 = x
    234.56 = y
    67.78 = z
    Deck = description of the feature or object

    The difficult part of the process is to join these points together to form a fair surface that represents a true model of the boat. The best model is one that can be produced from as many points as possible but a table-of-offsets will only generate points at possibly 2' stations at best! Joining thru the points can provide a NURBS line in Rhino or a 2-D polyline in AutoCAD but be careful because splining these lines does not honour the original point positions! A "fit-line" in AutoCAD works better but can only be accomplished in 2-D.

    Lofting in Rhino is pretty good but you will definitely see "kinks" at each station. As far as I can tell, the only way to eliminate these is by eye. If anyone knows otherwise, please let me know! Rhino wil also do some interseting stuff that can't be explained by humans! Often a "bowtie" or complete abberation of surface lines is created for no apparent reason. The only solution I have found is to drink excessively! (only kidding)

    I hope this information may help but anyone needing further info can conmtact me at:
    fmee@rogers.com
     
  8. CGN
    Joined: Jan 2003
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    CGN Senior Member

    Hi this is a spreadsheet CSV (format), and I included a RhinoV2 file with the way it is supposed to look the CSV file once is open with rhino.

    that's is if your reading the file from an offset table, but if you are reading form a hull design software and you can't make it export into rhino, use the coordinates of the vertex of the surface (on the hull design software) and then input this ones into a spreadsheet save them as a CSV and open them in Rhino, once open, create a surface that has the same number or vertexes and drag the surfaces vertexes to match the vertexes points that you brought in first with the CSV file.

    and if is a polysurface explode this ones into single surfaces and do the same.
    but is really complicated.
     

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  9. snakefeet
    Joined: Sep 2002
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    snakefeet Junior Member

    straightening a bowtie

    mee, I think I know what you mean by "bowtie" in a lofted surface, and there is a way to fix that: first, delete the bowtied surface. Then go to the menu command <direction>. (I think the path is Analyze -> Direction but I'm on a Mac right now & can't verify) Then follow the dialogue instructions. You can check the direction of the curves and I believe that you can change the direction as needed.

    I can't explain the mathematics of it but I'm pretty sure that you want all the curves in a loft to be oriented in the same direction .... in a mathematical sense. What I mean is that, no matter what the shape of the curve is, curves in rhino have a direction sort of like the way vectors do (for all I know NURBS may be based on vector math). For instance, if all the curves in a hull were drawn from the keel up to the sheer, except one line was drawn from the sheer down to the keel. There will be a bowtie at that backwards line.

    I've found that, when building surfaces from curves (especially curves from other programs &/or other firms) it pays to check the direction of all curves, check the number of control points and degree of all curves, and sometimes even to trace over them in rhino and trash the originals so you know they're clean. I once tried to build a hull model from the lines plan in a set of drawigns from a yacht builder. After some strange results I zoomed waaaaaaaay in and found that in several of the aft section lines, the freeboard line came down to the inboard end of the chine line and the underbody line came to the outboard end of the chine line. I fixed that and the hull surfaced with almost no trouble.
     
  10. Polarity
    Joined: Dec 2001
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    Polarity Senior Member

    One thing with lofting surfaces to curves in rhino is that it is very sensitive to where you click the curve.
    These two surfaces were made from 2 identical sets of lines. When I lofted the one on the left I picked the curves at alternate ends. The one on the right I picked all the same ends... I will leave you to guess which is the one I wanted...

    Paul
     

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  11. PhotoBoatGuy
    Joined: Feb 2004
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    Location: Redmond, WA

    PhotoBoatGuy Rhino fanatic

    These suggestions all work in Rhino. Having modeled many boats in Rhino, I know the temptation to jump in at the deep end of the pool. DON'T

    It will serve you well, in this project and for years to come to start by learning how to model a boat, before working on something that counts. Take a very simple hull and create it from scratch. Learn to use the tools in Rhino that are designed to make your life easier. That way, you don't feel bad at the end of the day if you wind up trashing the whole mess.

    Then, when you are ready, you will find that typing a few coordinates is a very small part of modeling the hull. At that point, select whatever suggestion above seems to make the most sense to you and go with it. For my money, the scripting suggestion works best, since you can use the typed script file over and over till you get all the coords correct.

    As far as lofting surfaces from curves, if you preselect all curves and rebuild them, using the fewest points necessary to reliably duplicate the curves, you can then type the loft command and a surface with "clean" geometry will be lofted over the curves selected. An Isocurve will be present at each of the input curves, with a row of control points very near each isocurve.

    With these points and the various analysis tools (emaps, curvature maps, rendered displays, etc), you will be able to make the surface as smooth as you like.

    So, by all means, using a table of offsets will yield a hull, but learn to use the tools, first and you'll be glad you did.
     

  12. patrik111
    Joined: Sep 2003
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    Location: Sweden

    patrik111 Junior Member

    Not to geeky actually :)
    This is the first thing you see when opening Rhino help and click on Script.

    "This script creates a set of points from a list, selects them all, and fits a polyline through the points:
    ! _SelAll
    _Points
    -4,0
    5,1
    4,4
    -4,4
    13,-4
    8,-3
    1,6
    _Enter
    _Invert
    _CurveThroughPt"

    Just change the points to the one in your station.
    After that loft through the stations using the loft command

    You can just enter the points in any text editor and copy them and paste it into the command line.

    Good luck
     
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