Offsets to .csv file and into Rhino using Excel Spreadsheet

Discussion in 'Software' started by DCockey, Dec 9, 2021.

  1. DCockey
    Joined: Oct 2009
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    Location: Midcoast Maine

    DCockey Senior Member

    Also posted on the Rhino forum.

    First the short version. Instructions and tips may follow.

    Attached is an Excel spreadsheet I use for importing a table of offsets into Rhino as a set of 3D points. The spreadsheet uses the conventional system for units of feet and inches of writing the offsets as feet - inches (integers) - eighths of inches. For example 4-6-3 is 4 feet 6 3/8 inches.
    After entering the offsets on the first sheet the second sheet is saved as a .csv file, which can then be imported into Rhino.

    Example of a Mukilteo boat which was documented for the National Park Service by Jack Becker. The lines and table of offsets can be downloaded at 1. Lines and offsets table - 19' 6" Mukilteo Boat, The Center for Wooden Boats, Seattle, King County, WA 1
    Attached are:
    Excel spreadsheet with the offsets entered
    .csv file with offsets:
    Rhino 7 .3dm file with offsets as 3D points:
    Rhino 7 .3dm file with points sorted and initial curves:
     

    Attached Files:

  2. pafurijaz
    Joined: Dec 2016
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    Location: Italy

    pafurijaz Senior Member

    Hi, this tool is useful, but I opened the file and I saw that there are some misaligned areas and wavy profiles, are these errors present in the offset table,
    Or is this due to the curve through point used to build the splines? 
From these a wavy surface is consequently obtained.
    upload_2021-12-10_17-27-58.png

    Greetings
     
  3. DCockey
    Joined: Oct 2009
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    Location: Midcoast Maine

    DCockey Senior Member

    There are multiple reasons for the waves in the curves which were created directly from the points with no editing or fairing.

    The plans used as the source of the offsets were made from an existing, old boat which was not as fair as a new boat. From the notes on the plans: Vessel was documented "as is" with not attempt to correct for distortions due to age, deterioration, or deformation.

    There may be mistakes; either in the original table of offsets or in what I typed into the spreadsheet. I checked what I typed and corrected several errors. Judgement is needed to determine if there are errors in the original table of offsets.

    The precision of the offsets is limited to 1/16 inch. When a curve is interpolated through two points which are close together compared to the spacing between other input points waves frequently occur. This is the cause of the waves in several of the station curves.​

    I use points from a table of offsets as initial data for creating a hull surface. The file I uploaded with the curves shows the initial sorting and inspection of the imported points. There is considerable work needed to create a fair surface based on the points.
     
  4. pafurijaz
    Joined: Dec 2016
    Posts: 265
    Likes: 51, Points: 38, Legacy Rep: 18
    Location: Italy

    pafurijaz Senior Member

    OK, I too have found errors in an offset table, of a hull, which I transcribed in 3D space with the points, and I had to review the areas out of alignment.
     

  5. DCockey
    Joined: Oct 2009
    Posts: 5,170
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    Location: Midcoast Maine

    DCockey Senior Member

    Notes on entering offsets in the Excel spreadsheet

    Do not make corrections in the Excel spreadsheet by dragging the contents of cells. The result will be errors in the output. Dragging cells in the spreadsheet will change the references in the formulas used to create the sheet for the .csv file. If you make a mistake and type input in the wrong cells then back up and type it in the correct cells.

    Each offset location has three cell for feet, inches and eighths of inches respectively. This follows the standard format used in tables of offsets. In the spread sheet it is permitted to enter values for greater than 11 and values for eighths greater than 7. Also the values entered do not have to be integers. For example the following are equivalent:
    5 feet 3 inches 1 eighths
    0 feet 63 inches 1 eighths
    5 feet 3.125 inches 0 eighths
    0 feet 63.124 inches 0 eighths
    All of the above result in 63.125 as the value in the .csv file.

    Negative values can be entered for offsets. This can be useful if points are desired below the baseline for example. The entry in each cell needs to be entered as a negative number. For example -2 feet -7 inches -2 eighths results in -31.25 in the .csv file. If -2 feet 7 inches 2 eighths is entered instead the result in the .csv file will be -16.75 in the .csv file.

    Entries in tables of offsets frequently contain “+” after the number of eighths. This usually means to add 1/16 inch to the offsets. I add .5 to the number of eighths when entering the corresponding value in the spreadsheet. For example 1 5 2+ is entered as 1 5 2.5
     
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