evaluate surface

this definition is thanks to andrew kudless from matsys. during a rhinoscript workshop at cal poly, he quickly showed us how to obtain the normal from a surface in grasshopper


  • evaluate surface
  • vector scalar multiplication
  • vector vector summation

19 Responses to evaluate surface

  1. Rundial says:

    same problem as everyone else
    and the link
    “Here is the build for grasshopper 0.8.0052
    https://files.me.com/semorse/w1loz1” is no longer available
    if someone has a grasshopper file for this so i can what i’m supposed to substitute that’d be great
    i can’t seem to figure out the math otherwise

    please help
    i’m stuck on this BIG TIME!

  2. rufus says:

    using build 0.8.0063
    already FAIL at 00:28 as i connect the Pt XYZ to UV, Eval turns red and gives me the Runtime Error:
    “1.Invalid cast: Surface >> Brep”

    have found no advice in forums, please help me out here!
    what is the problem??

    • rufus says:

      OK found the solution:
      i redrew the curves, who used to be fragments of circles
      for some reason grasshopper didn’t like them.
      after redrawing them, lofting didn’t bring the desired outcome, was tangled up, until i mirrored one of the curves, so, apparently it does matter from which curve end i start drawing when lofting, is that correct!
      lofting the curves so that the curve endpoints connect, as well as the startpoints connect, finally gave the solution.

  3. federico says:

    hi, there is any possibility to build this tutorial for grasshopper 0.8.0052 thnx!

  4. thomas says:

    Can you redo this for the new version? The lack of a vector multiply function is a real spanner in the works!

  5. Shawn says:

    Here is the build for grasshopper 0.8.0052

    • Shawn says:

      Since MobileMe have been replace with iCloud, iDisk will be no longer be available after June 2012.
      So I have removed the .ghx file.

      In regards to the reason for just submitting the correct build for the latest grasshopper version.
      Rather than explain it I thought it might be easier to just show what the others have been referring to as
      “math multiplication and math addition.”

      The laster grasshopper has made the the math functions “context-aware.” Meaning if the input is a vector
      value the math functions will read it as a vector. So the vector multiplication and summation just become
      math multiplication and math addition.

      Hope this helps.

      • Shawn says:

        Seems I had some HTML input error. Sorry for the inconvenience but could please fix the broken sentences in my last post when you moderate it?

  6. Ben says:

    there is a problem in the lates grasshopper build… can’t figure out how to “eval” on a surface….

  7. tnunz says:

    If you’re using the latest GH, the standard Addition and Multiplication functions are used in place of Vector Summation and Vector Multiply, respectively. This should get you what you’re looking for.

  8. deniz says:

    Dude, i’m using grasshopper 08.0052 and i can’t find a SUM function from the vector menus. I have used Vec2pt instead of the Sum in this tutorial and it did not come up with the things i expect it to be. For example in my screen there is no normal vectors which is perpendicular to the surface. Instead of that there is a huge vector pipe which seens like a ray, so too big and not a normal of the surface.It makes weird angles to the surface.

  9. Jo. says:

    I am sorry I dont understand how to make the product line map to the surface of the loft?

    I am using version 8.0051 and therefore using Amp and Xproduct as noted above…. can you explain what you mean by ‘there is a PLUS to the math addition’? if this is what I am after…?


  10. Timothy says:

    Just cant get it to work in the latest GH. Instead of multiply I used Amp. and instead of Sum I used XProd. The line comes out of the normal position but it is ending in weird places and so is not he actual normal. Please can you explain in new GH?

  11. Peter says:

    Can’t guess what shold be done instead in the new GH version. :(

  12. peter says:

    There is a PLUS to the math addition – the math addition is an overriding function and is not restrained to numbers only, for example, it adds objects that add for example a point and a vector.

  13. Raymond Chau says:

    Thanks for the tutorial! But I am wondering how I can determine the normal from a point on the surface if I only know the x,y,z coordinates of the point?

  14. marek says:

    Hi, good work… but vector scalar multiplication and vector vector summation don’t exist in GH build 08.004 :-( the solve is math multiplication and math addition… pls write “about this” in web under to topics, it will be very helpful for any beginners like me ;-) thanx

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