Logarithmic spiral with equation

[svantevid]

I'm trying to create a Logarithmic spiral in Creo. I used the equation bellow, but the "shape" of the curve I get is not correct (I compared it to a curve from Graph software and calculations of intersection properties with a circle with 129,4mm diameter). 

Equation in Creo:

a=1
b=0.3
x=a*exp(b*t)*cos(t*360)
y=a*exp(b*t)*sin(t*360)
z=0

Screenshot from Creo:

https://i.imgur.com/tWBBViU.png

Screenshot from Graph software:

https://i.imgur.com/4FsrHMf.png

Does anyone know why I cannot get the correct shape? I also tried with polar (cylindrical) csys and get the same results.

[MartinHanak · Accepted solution]

Hi,

use following equations

a=1
b=0.3
n=4
x=a*exp(b*t*2*pi*n)*cos(t*360*n)
y=a*exp(b*t*2*pi*n)*sin(t*360*n)
z=0

Note:

In Graph software sin() an cos() functions use values in radians. In Creo sin() an cos() functions use values in degrees.

[svantevid]

Martin, thank you very much!