Import Lines Plan to Rhino

Discussion in 'Software' started by ivansalasj, Nov 15, 2006.

  1. Tim B
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    Tim B Senior Member

    Importing a raster image into Rhino is easy. Goto

    View --> Background bitmap --> Place

    Now specify top right and bottom left corners. Simple.

    Raggi, Autocad is not as accurate as Rhino, be careful with tolerances. I usually work in meters and use tolerances of 0.00001 (ie. a hundredth of a mm). I honestly don't think I'd start playing with lines plans in AutoCAD. It's good for producing 2D drawings, not designing boats.

    Normally, when you're tracing lines, you keep the degree the same for all curves (degree 3 is usually ok), but use as few control points as you can get away with.

    I didn't know Rhino could handle PDFs is that just Rhino 4?

    Cheers,

    Tim B.
     
  2. Raggi_Thor
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    Tim, we use the tools we have and know :)

    What happens to your background image in Rhino when you zoom and pan while you draw?

    AutoCAD is very good for tracing raster images :) it's easy to pan while you are drawing.
    Rhino 3.0 can import pdf.
    I don't think a raster image in a pdf or converted to pdf will give you anything useful as an import, BUT a lines drawing printed directly from any cad program to pdf will be imported as lines or curves to Rhino.

    AutoCAD is more than accurate enough for 2D drawing. Double precision floating points, normally 16 decimals or so.
     
  3. Tim B
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    Tim B Senior Member

    Panning and zooming with a raster image in rhino is just like panning or zooming any other object.

    Raster images in PDF files will remain as raster images for obvious reasons. Whether all PDF files are written from CAD with curves as curves I wouldn't like to say. Certainly any CAD software based on the Linux/Unix system will, as the process is esentially writing to a postscript file, then printing from there. Others, particularly on Windows (which I think uses a raster printer driver) may be different.

    AutoCAD has, in the past been known to trim lines to the screen position of the cutting object. When the cutting object is a circle drawn from eight lines that's quite a deviation. Further to that, I've rarely found it easy to import/export to/from AutoCAD.

    As far as I'm concerned, AutoCAD is not good enough to warrant the money. Especially when QCAD is available for a hundredth of the cost.

    Tim B.
     
  4. Raggi_Thor
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    OK Tim, I'll have another try on backgrounds in Rhino.

    What you say about AutoCAD is obviously wrong. How do you think large production industries could live with that for 20 years (the TRIM command was introduced in R2.5 in 1885 or so)? Where does myths like that come from? I don't remember how it was in R2.7 in 1985, but in R9, from 1987, I am pretty sure trimming of lines have been as accureate as you can do it with double precision in C(++?). btw, that was on Ultrix :) on DEC Alpha Sparc(?) something.
     
  5. Raggi_Thor
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    Tim, we are a bit off topic, but I just tested a plot from BricsCad (low cost acad clone) to pdf through Win2Pdf (low cost pdf writer) and opened it in Rhino. All objects are curves in Rhino. Splines and arcs from BricsCad have too many control points though.

    I agree that AutoCAD is too expensive, that's why I use and sell BricsCad, just 225 Euro :)
     
  6. Tim B
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    Tim B Senior Member

    No, I don't think I'm wrong, I saw it happen in R12, It trimmed it perfectly accurately, just not to where the circle should have been mathematically. I had a play with Rhino's import PDF function, and it seems it should be used with care, but it's a rather handy feature. it seems to struggle on PDF files that are larger than A4, and line widths greater than 0.

    I'm using QCAD for 2D Drawing work now. it's by far the best package I've found to date.

    Tim B.
     
  7. Steve Baer
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    Steve Baer Rhino Developer

    I'm a developer for Rhino. Do you have a model that displays this behavior that I could look at?
    Thanks,
    -Steve
     
  8. Steve Baer
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    Steve Baer Rhino Developer

    Hi Raggi,
    Rhino has two methods for displaying raster images in the background.

    The first is called "WallPaper" which can be accessed through the ViewportProperties. Wallpaper just displays in the background and has no relationship to physical sizes in the model. It does not change when you pan or zoom. It sounds like this is what you are currently using.

    The second is called "BackgroundBitmap". This is a rectangle that you can place, rotate, and scale in rhino. It lives in world coordinates and moves when you pan, zoom and rotat in your viewport. This is what you should be using for tracing raster images like scanned in lines plans.

    Thanks,
    -Steve (Rhino Developer)
     
  9. Raggi_Thor
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    Thanks Steve, now I understand :)

    And Tim, you are a stubborn one, and this is annoying me more than it should :)
    I can install R12 here, just have to find the cd, but in Acad R14 (from 1997!), 2000, 2005 and 2007 it works OK. Even if you have coarse settings for display resolution (which is a good for complicated drawings on slow computers), well anyway, even if the circle looks like a six sided polygon on the screen (before you regen), the trimming is of course accurate.

    Another myth (I hope) that I like to believe is that Microstation has a finite set of points in every drawing, so that if you have a very large ship, small items is impossible to draw accurately. This is the contrary to acad, where you can draw the sun, the earth and the moon and the the little plate saying "Neil was here"!
     
  10. Raggi_Thor
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    Couldn't resist...
    http://www.intelcad.com/pages/autocad/index.htm

    I site:
    Many of the designers using CAD today don't fully realize the magnitude of accuracy provided by AutoCAD. Often in the past I could hear polemics, where Intergraph IGDS and Microstation users were "proving" that "their" software is better in all respects, one of them being accuracy. This was never the truth, as even in its infancy, in the early eighties, AutoCAD was using double precision floating numbers to store and process DWG data, where IGDS was using 32 bit integer cube to define space positioning of its elements.

    Read on, and once you are through, download SOLAR.DWG and go on your interplanetary trip to witness AutoCAD accuracy :)

    How much more precise is a double precision number from a 32 bit integer?
    A double precision number uses 64 bits (8 bytes) to represent a single floating point number - twice as much as a 32 bit integer. Of these 64 bits, one is used for sign, 11 are used for exponent and 52 are used to define mantissa.

    Graphical representation of such a 64 bit number would be:

    S EEEEEEEEEEE FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF

    where:

    S - sign bit, 1 means negative, 0 positive
    E - each E means one bit of exponent. 11 bit number can represent values from -1022 to 1023
    F - each F represents one bit of a mantissa. 52 bit mantissa can represent 4503599627370496 fractions.

    32 bit integer cube can represent 4294967296 discrete points in each of the three directions.

    Below is a translation of what these numbers will mean to the processing and storage of CAD entities.

    If you will try to draw a drawing that extends 4 km in each direction, Microstation's 32 bit format will limit your accuracy to 0.001mm. The same size extents in an AutoCAD drawing can be drawn with an accuracy of 0.000000001mm - that is a million times more accurate.

    One could say "one accuracy is high enough and another is overkill, so what?". But then, he doesn't realize that with almost EVERY geometrical operation performed on an entity, the accuracy is reduced. When entities are moved, rotated, scaled, stretched etc., complex mathematical transformations are being applied to their geometry. The results are stored back in the drawing database: in AutoCAD with double precision floating point accuracy, in Microstation with 32 bit integer accuracy. Both, math transformation and storage, are REDUCING the accuracy of a drawing. Where an AutoCAD user can safely ignore a 3 or 4 significant digit reduction in accuracy in a drawing that has been modified thousands times over the years (he still has 12 precise digits), the same cannot be said about a Microstation user that has maximum of 10 precise digits and loses 3 of them in complex processing).

    To showcase the power of AutoCAD detailing, Autodesk was including in earlier releases of AutoCAD (I think, up to R12) the simple, yet very impressive, 2D drawing file SOLAR.DWG (drawn in 1983 by John Walker, co-founder of Autodesk). You can download this file below (when you finish reading ;).

    I will always remember my first "interplanetary" DWG travel that I did in 1985, after learning how to zoom:

    after you open the drawing, you are looking at a whole solar system from outer space, drawn to scale in kilometers as DWG units.
    zooming into blob at the center reveals an inner solar system with a few orbits, a 3-rd of them being Earth's, with the Sun in the center.
    On the Earth orbit you can see a small flickering dot. Zoom in on it, the larger circle is Moon's orbit around Earth, the dot in the middle is Earth.
    On Moon's orbit you can see a flickering dot. Zoom in on it, it's Moon.
    On Moon you can see a flickering dot. Zoom in on it, you will see the crater.
    Near the crater (200 meters from it) you can see small green item. Zoom on it, it's LEM, the landing module that brought Neil Armstrong and his colleagues to the Moon.
    On the leg of LEM you can see a 30cm plaque. Zoom in on it and you can read the message:
    HERE MEN FROM THE PLANET EARTH FIRST SET FOOT UPON THE MOON etc.
    signed by three astronauts and president Nixon
    One day, when I have some time I'll add solar.dwg screen shots to this web page.

    Now download SOLAR.DWG (don't worry, it's just 10kB, 15 years ago my computer had 20MB hard disk and "huge" CAD files had 200kB). Start your (CAD) engine and take off on your interplanetary trip. Let me know how it went when you come back.

    For Microstation accuracy believers, with all their tools starting with "ACCU", for accurate ;) I propose the following form of treatment:
    Try to replicate SOLAR.DWG (drawn 17 years ago on AutoCAD!!!), make it into SOLAR.DGN ;) with today's Microstation (XXI century). This 17 year old, 64 bit double precision DWG, can have everything in the Solar System positioned with an accuracy of a few millimeters (you can read 3.7mm text on a plaque). With DGN, the smallest item that can be drawn in this drawing (showing orbit of Pluto, 11916840000 km diameter) is a 3 kilometer line, both endpoints being positioned with 3 kilometer "accuracy" in X, Y and Z direction.

    Alex Januszkiewicz
    alexj@intelcad.com
    Former President / Principal Programmer
    IntelCAD Systems / DWG Data Recovery Services

    PS. Do I have any Microstation background to make these kind of discussions? Even though I spent the last 15 years programming mostly for AutoCAD, I did a lot of MDL development for Microstation, PDS and Frameworks clients over the last 10 years. To this date I develop, from time to time, commercial grade, complex MDL programs, on site of a large company in Calgary that uses both AutoCAD and Microstation/PDS. I know Microstation and its DGN format in and out.

    ******************************** end site
     
  11. ivansalasj
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    ivansalasj Junior Member

    Raggi Thor:

    In the last posts we have surely deviated, I have been away at sea for several months and I am back working on my designs.

    I have traced the lines in Autocad from an imported image of the lines plan of the yacht I am currently working on. My query now is that I would like to carry out the hull modelling in Maxsurf rather than in Rhino, primarily because I have used it on previous designs and I am used to it.

    I can create the surfaces in rhino to match the lines I have imported from Autocad and faired with Rhino, and then export these surfaces to Maxsurf for modelling and hydrostatic calculations, is that a good way to do this or its better to continue the hull modelling in Rhino, which I have never done!

    Any suggestions?

    Cheers

    Ivan
     
  12. Crag Cay
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    Crag Cay Senior Member

    Hi Ivan,

    I still think you are making this overly complicated. As I suggested in my previous posts, doing the whole thing in Maxsurf is straightforward and quick.

    Once you have the scanned lines planes imported into the background of each view and scaled, open a surface and get modelling. The more experience you have the quicker you will be able to establish the control net required, but a long keeled hull is quite straight forward.

    Then get the sheer and keel /bow / stern profiles established with the edges of the surface, before working on the hull shape. Establish your section grid to correspond to the original stations on the drawing and try to make sure you have a control column close to the key stations. Then work in the Body Plan view with the section display off. You will then get a single line representing the section you want to work with and its corresponding control column.

    But again as I said earlier, when you fair the lines you will do a better job than the original lines plans as you will be doing the lofting stage as well. So depending on whether the original lines were done well, and whether the plans you have are not distorted, etc, will effect how close your Maxsurf model will be to the original.

    Once you have your model you can then do the hydrostatics in HydroMax. I would export it to Rhino for 3D detailing.
     
  13. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    Even if I like AutoCAD/BricsCad and Rhino I have to agree with Crag.
    Every import/export is an extra hassle.
     
  14. Tim B
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    Tim B Senior Member

    So what we need is automatic sections, buttocks and waterlines in Rhino.

    Why didn't I think of that earlier?

    Tim B.
     

  15. Steve Baer
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    Location: Seattle, WA

    Steve Baer Rhino Developer

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