sirclippliers Posted April 24, 2011 Posted April 24, 2011 Hi, I am trying to follow some directions and the call for a spline to be drawn onto an image. I can only find a polyline which doesnt work like I need it to. As I understand it a polyline will put a curved line as close as it can to a series of points, whereas a spline will "join the dots". I need to join the dots but with a curve not a jagged straight edge. Can someone tell me where the spline is please. Many thanks, Dave. Quote
eldon Posted April 24, 2011 Posted April 24, 2011 As I understand it a polyline will put a curved line as close as it can to a series of points, whereas a spline will "join the dots". I am not sure that you have got that correct. If you draw a polyline as a series of straight lines, and then curve Fit. The resultant curved polyline passes exactly through the points. A spline also "joins the dots" and you should find it in the Draw menu. Quote
Tyke Posted April 25, 2011 Posted April 25, 2011 (edited) Eldon is correct, a polyline always passes through all of the points. Curve fitting a polyline will give you a curved line that still passes through all of the points, but curve fitting a polyline will also increase its length. A spline only passes through all of the points when its Fit Tolerance property is set to 0, a value greater than 0 will move the spline away from the points, the bigger the value the bigger the distance from the points. As far as I know a spline does not have a length property, so getting the length of a spline is not so simple if you need it. Perhaps you can get it programmatically. If you can Lee Mac will know how to do it. Edited April 25, 2011 by Tyke Quote
sirclippliers Posted April 25, 2011 Author Posted April 25, 2011 Ahh, found it, The text I have here states "a B Spline is a curve that passes near a set of control points whereas a Bezier curve passes through a given set of control points". Is that correct or am I trying to follow a tutorial written by someone who doesn't know. Its a B Spline I need, is that the default on AutoCAD? Quote
eldon Posted April 25, 2011 Posted April 25, 2011 Ahh, found it, The text I have here states "a B Spline is a curve that passes near a set of control points whereas a Bezier curve passes through a given set of control points". Is that correct or am I trying to follow a tutorial written by someone who doesn't know. Its a B Spline I need, is that the default on AutoCAD? If you use the Spline command, it will draw a Bezier curve which is a special case of a B-spline curve. It is a polynomial curve defined by a set of control points, representing an equation of an order one less than the number of points being considered. If you use the Polyline command, you can curve fit the resultant straight line sections with a Spline fit, which gives you the B-spline curve, which does not pass through the control points (except the first and last). If your instruction calls for a Spline curve to be drawn, then I would hazard a guess that you should be using the Spline command. (I am not really that clever, but I do know where to find information in the Help files) Quote
sirclippliers Posted April 25, 2011 Author Posted April 25, 2011 Indeed, as Albert Einstein once said "knowledge is not the retention of information, its knowing where to find it". He also said that compound interest is the eighth wonder of the world but thats irrelevant here.. Thanks for the info though, I'm going with the spline. Quote
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