Hi John, There are various types of spirals that are defined mathematically, so you might want to investigate a bit further to determine one that fits your needs and is pleasing to the eye.
The simplest type (and probably what you are looking for) is the Archimedean Spiral, whose definition is r = a * theta, where r is the distance from the origin, a is an arbitrary constant and theta is the angle from the x axis. This is actually a special case of r = a * theta ^ (1/n) where n defines how tightly the spiral is wrapped, and for the Archimedean Spiral is 1. Other values of n give other types of spirals. A more elegant spiral is the logarithmic (or equiangular) spiral which is the shape of the many-chambered nautilus shell. It is defined by r = a * e ^ (b * theta) where r is the distance from the origin, a and b are arbitrary constants, e is the natural log and theta is the angle from the x axis. It is interesting that this is also the shape of the cam devices that are used in rock climbing for jamming in cracks...the spiral has an interesting characteristic that make it suitable for this application. These formulas are in polar coordinates, and most programs plot using cartesian (x,y) coordinates, but the conversion is easily done. This may sound complicated, but drawing spirals is quite simple mathematically and to program, especially compared to something like a gnomonic projection. I write programs in Visual Basic that draw in Adobe Illustrator, so I can't help you with the specifics of Delta CAD. If you would like, I can send you samples in .dxf that you could probably import or a .jpg format to show you what they look like...or a simple search on the web will show the similar. Tom Kreyche -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of John Carmichael Sent: Sunday, October 06, 2002 12:16 PM To: Sundial List Subject: Drawing Spirals? Hello all: Does anybody know how to draw a good spiral using Delta Cad? Or maybe there is some other program that will draw spirals (spirals can be drawn with different parameters) and I can import the drawing into DC as a dxf or bmp. The only way I can think of doing it on Delta Cad is mechanically. But this is very tedious. (see photo. First draw concentric circles, then add progressively longer radii from the center at the desired intervals around. Then I connect the radii endpoints with a spline). thanks John John L. Carmichael Jr. Sundial Sculptures 925 E. Foothills Dr. Tucson Arizona 85718 USA Tel: 520-696-1709 Email: [EMAIL PROTECTED] Website: <http://www.sundialsculptures.com> - -
