Accurate Sine Wave PATH?

Asked by isnb on 2008-09-05

How do I draw a path that has the exact shape of a sine wave?

To clarify, I don't want to draw an approximation of sine wave, using the inaccurate hand/mouse movements. Rather, I would like to draw a sine wave (or control its properties) similar to the way I draw a circle, a rectangle, etc.

Is this possible in InkScape?

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isnb (member57140223) said : #1


From :

How can sine curves be made in Inkscape?

Inkscape includes an extension called Function Plotter. It can be used to create sine curves or any other function graphs. To access it, go to the Effects menu, and then the Render submenu. Other software, such as Xfig, KiG, or KSEG can also be used to create complex curves and then export to SVG for use in Inkscape.

Effects > Render > Function Plotter...

Now I have to figure out all the mind boggling input fields... :-)

Help would be appreciated.

Alvin Penner (apenner) said : #2

- draw a rectangle, make sure that it is selected or highlighted
- click on Effects | Render | Function Plotter
- in the Function textbox, type sin(x)
- for y value of rectangle bottom, type -1
- for y value of rectangle top, type +1
- similarly you can customize the start and end x values to suit your taste.

The actual refresh, or update, process for the sine wave is not entirely clear to me, I find the most convenient thing is to simply delete the rectangle entirely and draw a new one, the Plotter routine will remember all your settings so you can simply hit Apply again, once you have a new empty rectangle selected.

isnb (member57140223) said : #3

Thank you for your answer. It was very helpful for figuring out the myriad of options there and generating my first sine wave. However, the generated sine wave appears modulated, not on a straight line - and its amplitude far exceeds the dimensions of the rectangle. What am I doing wrong?

Here is a snapshot of what I received:

And here are the settings that I used to generate it:

Any idea why the generated sine wave appears like that?


isnb (member57140223) said : #4

Ah! I think that I got it. :-)

Here is what I did:

1) I unchecked the "Multiply x-range by 2*pi" checkbox (and specified and End x-value of 360)

2) I increased the number of Samples from 8 to 128

3) I checked the "Isotropic scaling" checkbox.

I think that #3 was the most important one. It's so confusing... what does "Isotropic scaling" mean?

isnb (member57140223) said : #5

This is really weird: the "Multiply x-range by 2*pi" checkbox is the one that effects the sine wave "modulation"... Why???

To better explain: If I check that "Multiply x-range by 2*pi" checkbox, then the sine wave draws around a perfectly horizontal line. Otherwise, it draws around another sine wave... Weird. What's the connection between modulation and changing the unit system to be radian based???

Alvin Penner (apenner) said : #6

you are probably seeing the effects of what is known as "aliasing", which is what happens when you don't sample a signal fast enough to catch all the variations. Try using a smaller x range and a larger number of samples.

for example, start x = 0, end x = 2, check mark on multiply range by 2*pi, samples = 8 , will give you a well-behaved sine wave with exactly 2 full cycles.

Can you help with this problem?

Provide an answer of your own, or ask isnb for more information if necessary.

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