[Bf-docboard] Re: sine wave errata

[Stefano Selleri]

Argh... I must redo the image too :(

Stefano
  ----- Original Message ----- 
  From: Randall Rickert 
  To: bf-docboard at projects.blender.org 
  Sent: Tuesday, October 18, 2005 6:45 PM
  Subject: [Bf-docboard] Re: sine wave errata


  Sorry, looking at it closer, the documentation says:


    The actual width of the area in which the single pulse is significantly non-zero in Blender Units is given by 4 over the Narrow Value. That is, if Narrow is 1 the pulse is 4 Units wide, and if Narrow is 4 the pulse is 1 Unit Wide.


  It seems this formula should be 4 over twice the Narrow value i.e.: 4/(2*Narrow), not 4/Narrow. I tried different values to get closer to a sine wave, such as Pi/(2*Narrow). It's really not possible to make a sine wave in Blender, because the pulse is a Gaussian function or such, not a sine function. 4/(2*Narrow) makes the wave very smooth, but the peaks are a bit more narrow than the valleys.


  My suggestion of Pi/(2*Narrow) looked more like a sine wave, but it makes a subtle crease in the valley. 4/(2*Narrow) is a better formula, and is probably the formula the original author intended when they wrote "4 over Narrow".


  -Randall




    Date: Mon, 17 Oct 2005 03:27:55 -0700
    From: Randall Rickert <randall at rickert-digital.com>
    Subject: [Bf-docboard] sine wave errata
    To: bf-docboard at projects.blender.org
    Message-ID: <8E36C3EA-5636-493F-BA71-51DBFD628C43 at rickert-digital.com>
    Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed


    In the user documentation on this page:
    http://download.blender.org/documentation/htmlI/ch21s03.html


    It says:


      To obtain a Sinusoidal-like wave


      To obtain a nice Wave effect similar to sea waves and close to a  
      sinusoidal wave it is necessary that the distance between following  
      ripples and the ripple width are equal, that is the Width Num  
      Button value must be equal to 4 over the Narrow value.


    There is a nice diagram also. Both the diagram and the text are  
    incorrect. The formula Width=4/Narrow does not create something like  
    a sine wave. This is easy to see if you try using the values Width=4  
    and Narrow=1. The result does not look at all like a sine wave.


    As far as I can tell, the formula for a wave that looks sinusoidal  
    should be Width=Pi/(2*Narrow). Probably a better way to write it is  
    Narrow=Pi/(2*Width), because most people would probably start with a  
    wavelength in mind (the wavelength is Width*2).


    It's a bad interface anyway, because making a sine wave (probably the  
    most common wave the user will want to make) shouldn't require the  
    user to calculate Pi/(2*whatever).


    -Randall




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