ploting a spiral

[mong35]

thread770-141275 <--- this also helpt me understand a little about polar coords and cartesian coords. thanks.

hi guys. i want to plot a fib spiral in excel. the catch is i want to give the x1,y1 and x2,y2 as starting points on a cartesian plane.

so it will look like this

http://www.mcs.surrey.ac.uk/Personal/R.Knott/Fibonacci/GoldenSpiral.xls

using 1.618 as the expansion factor. but in this example it just starts and goes. this is where i'm having trouble.
i can calculate the angle and distance from x1,y1 x2,y2 but how do i transpose this into this spreadsheet to give me my spiral in the proportions i need them in???

once i have my spiral the correct size and pitch then i will transpose it to the cartesion plane i need it on. this is no problem. any help would be appreciated. thank you.

so to recap. let x1,y1 be 0,0 and start the spiral at x2,y2 ANYWHERE on the plane! so for distance(radius) and angle start drawing spiral to the proportions of (distance). what is the correct excel formula for this. the url is close. but i don't understand what to change.

mong35

p.s. i've made a partial (first 6 arcs) spiral using 1/4 arcs but the damn thing is hard coded and very messy. i know the solution will be very easy and simple.... lol.

 

[IRstuff]

Is this for school?

TTFN

FAQ731-376

 

[dimjim]

Cant you simply draw it at 0,0
and then move the whole thing from 0,0 to
x2,y2?

 

[mong35]

lol. no its not for school but feels that way. lol.

i found a workaround but i'm still not 100% about the scaling. even though it looks proportional. the thing is if i change the x value to pixels then my y scale will be off the chart. anyway here i'm using 7 increasing quarter circles. i can rotate it clock or anti clockwise and adjust the pitch. so will do for now. i'm going to try write a function in basic now to do this.

thanks for reading my post.