On 12/01/2014 06:52 PM, Jon Elson wrote: >> All CNC machines use turtle graphics in 2D, 3D, 4D, etc. > No, turtle graphics is a scheme where the coordinate system is > centered on the turtle, and everything is relative to which way the > turtle is pointing now. So, if the turtle makes a 90 degree turn to > the left, and then moves forward, it will go in a different direction > than it would have before turning. So, the only operations permitted > are turning left or right by some angle, and moving forward in > whatever way the turtle is pointing.
That I would call a semantic interpretation. Whether you turn the turtle or the coordinate system is a matter of frame of reference, which, mathematically, is a simple trick. The distinction is IMO irrelevant as you can always define the exact transformation matrix to any frame of reference (and we are not going to come close to speed c). Your assertion does not hold entirely, because some machines have a rotational axis, which alter the coordinate system, as seen from the object under construction. The point of "turtle graphics" is that the the point-of-operation is a continuous and uninterrupted curve (in the zero order; derivatives may be discontinuous). A milling bit does not magically appear/disappear at the operator's whim and will thus follow a continuous path in the zero order with respect to the object. (let us not split hairs on doing tool-changes) > Most CNC machines have a fixed coordinate system, with an X axis, and > a Y (or Z) axis that is 90 degrees to the X. There is no operation to > turn left or right, and a +X move will always be in the same > direction. Actually, the /machine/ usually has a fixed frame of reference. The programmer is welcome to use a different one as long as it is ultimately translated to the machine's coordinate system. As I said, it is a matter of frame of reference. -- Greetings Bertho (disclaimers are disclaimed) ------------------------------------------------------------------------------ Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server from Actuate! Instantly Supercharge Your Business Reports and Dashboards with Interactivity, Sharing, Native Excel Exports, App Integration & more Get technology previously reserved for billion-dollar corporations, FREE http://pubads.g.doubleclick.net/gampad/clk?id=157005751&iu=/4140/ostg.clktrk _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
