# Help to understand why the sine wave from a curve line is not the same lenth of the curve line?

I have problem -Please help me to sole the problem of the length if you can tell me reason i will be gratfull

• Well now if you think that blender generated modifiers like sin or cos phases and lengths can be understood; please enlighten me sometime. But the bottom line is that -- while ESL is difficult -- you'll get little help from what is here. Put yourself in the place of the helper. What would she/he ask? When you helped someone: what information would be valuable (here) to invoke a response? Avoid emotions; frustrations about the software: 3D modeling and animation is very arcane software. Click on Edit under your question when you have more information. Feb 7 at 3:22

The solution is quite simple: if you want the sine wave to have the same dimension on X as the straight line, they should both start at the same X value and end at the same X value.

But you are plugging the Position vector into the float X input of the Combine XYZ node. A vector $$\vec{v}=(v_1,v_2,v_3)$$ will be converted into a float value by averaging the three values:

$$f(\vec{v})=f(v_1,v_2,v_3) = \frac{v_1+v_2+v_3}{3}.$$

In your case the three components are the $$x$$, $$y$$ and $$z$$ values but since $$y,z=0$$ this results in

$$f(x,y,z) = \frac{x+y+z}{3} = \frac{x+0+0}{3} = \frac{x}{3}.$$

Which means, while your straight line goes from -7 m to 10.1 m, the resulting sine curve only goes from $$\dfrac{-7}{3}\approx -2.3333$$ to $$\dfrac{10.1}{3}\approx 3.3667$$ so it is only one third of the original size.

What you need to do is use a Separate XYZ node to get the individual X float values so you can plug them into the X input of the Combine XYZ node to keep them the same as before. Oh, and by the way if you do not have a specific reason for the Transform Geometry node, you can achieve the same by entering -1.4 as Z value in the Offset vector of the Set Position node:

The other thing is: I do not know if this is intentionally (but probably not since you did not seem to care for separating the vector), the sine is now also just calculated for the -2.3333 to 3.3667 range. Maybe you want to use the separated X value there as well:

• Is there any way to use string to show the coordinate of the points of the sine ? -Because in the x goes from 0 to 5 is this value are in radiant ? Feb 7 at 13:03
• @KebabSharif Where does the x go from 0 to 5? The x goes either from -7 to 10.1 or -2.3333 to 3.3667 with the values in your question. The z values as result from $\sin x$ are ranging from -1 to 1 and with the offset from -2.4 to -0.4, but yes - the Math node takes the input as radians, not degrees. Feb 7 at 13:19