SYNOPSIS

coils [ -as? ] [ -r rotations ] [ -t tightness ] [ -w width ] [ -W width ] 
      [ -f filename ] [ -N object ] [ -o output_format ]

DESCRIPTION

The coils program produces an output file suitable for use with rendering programs that model coils or springs. Currently only POV-Ray include files are supported for output formats.

The final object is centered about the origin and the X axis. This means the left and right ends of the coil are equadistance along the X axis from the origin. The coordinates of both ends of the coil are provided in the comment section of the output file. No textures are provided.

OPTIONS

EXAMPLE USAGE

Suppose you want to create a coiled strand around a barrel, where each rotation of the coil touches its adjoining neighbor. Suprisingly, thats exactly why I wrote this little ditty. How would you do this? You need to know the following things:

1. The number of rotations the strand will make. 10 rotations should be enough for this example.
2. The radius of the strand. Lets say our barrel is 8 units long and will have 10 rotations in its coil, we'll need 8/(10/2)=1.6 units. Remember, this is the minor radius value for the torii that will make up the coil.
3. The radius of a complete rotation of the strand. We'll make our barrel 4 units in diameter, so the radius of a complete rotation of the coil around the barrel would be 2+1.6=3.6.
4. The distance between the apex of one rotation of the strand to the apex of the next rotation of the strand. This is the tightness. This is simply 2 times the radius of the strand, since each rotation touches its neighbor. For springs this value would be greater than 2 times the strand radius, so there is empty space between each rotation.

We also want two of these coils, with unique names but in the same include file. The include file should be called "mycoils.inc". We'll need to run the coils command twice. The first invokation would be as follows:

coils -r 10 -w 1.6 -W 3.6  -t  3.2  -f  mycoils.inc  -N coil1

The next invokation needs to tell coils program to append to an existing file. We do this with the -a option:

coils -a -r 10 -w 1.6 -W 3.6 -t 3.2 -f  mycoils.inc  -N coil2

Viola! You now have two coils named coil1 and coil2 that can be used within your POV-Ray scene file.

HOW DOES IT WORK

SEE ALSO

BUGS

It was quick and dirty and if you do stupid things it breaks. So, don't do stupid things.

The command line options use atof() to convert the input to a double. This only provides 6 digit precision unfortunately. I'm too lazy to convert this to a long double function so if you need greater precision you'll need to replace the atof() calls to your own version.

Torii are notorious for slowing the processing of an image. Although a bounding box around the coil helps speed processing, you should be aware that the coil itself will be quite slow to render, especially if you include a large number of rotations.

AUTHOR