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C Library Functions  - spirograph (3)

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NAME

spirograph(3f) - [M_drawplus] draw a hypotrochoid (LICENSE:MIT)

CONTENTS

Synopsis
Description
Options
Example
Author
License

SYNOPSIS

subroutine spirograph(xcenter,ycenter,sunr0,planet0,offset0,radius,ilines,ang,angs,ifill)

     real,intent(in)    :: xcenter, ycenter
     real,intent(in)    :: sunr0,planet0,offset0
     real,intent(in)    :: radius
     integer,intent(in) :: ilines
     real,intent(in)    :: ang
     real,intent(in)    :: angs
     integer,intent(in) :: ifill

DESCRIPTION

Draw a hypotrochoid generated by a fixed point on a circle rolling inside a fixed circle. It has the parametric equations

      x = (R+r)costheta-(r+rho)cos((R+r)/rtheta)
      y = (R+r)sintheta-(r+rho)sin((R+r)/rtheta)

where R is the radius of the fixed circle, r is the radius of the rotating circle, and rho is the offset of the edge of the rotating circle. The figure closes only if R, r, and rho are rational. The equations can also be written

OPTIONS

xcenter,ycenter
	center of curve
sunr0	radii of sun, planet, and planet offset
planet0
	radii of sun, planet, and planet offset
offset0
	radii of sun, planet, and planet offset
radius	radius to fit the shape to (no fit if radius is 0)
ilines	number of points to sample along curve
ang	angle to rotate the shape by, to orientate it.
angs	angle to start sampling points at; ccw is +; 0 is East
ifill	1 make a filled polygon, 2 make a hatched polygon

EXAMPLE

AUTHOR

John S. Urban

LICENSE

MIT License

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Nemo Release 3.1

spirograph (3)

June 29, 2025

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