Object Spline in AutoCAD
|AutoCAD drawing command|
|Spline in AutoCAD is smooth Bezier curve, which by default passes through specified points or deviates from them within tolerance. AutoCAD spline (complex) is piecewise smooth polynomial NURBS curve (NURBS - Non-Uniform Rational Bezier Spline) - non-uniform rational Bezier spline - Bezier curve, as special case of B-spline, passing near set of control points.|
|AutoCAD Spline tool is command that allows you to build smooth curves passing through specified points or near set of defining points, as well as defined vertices in shape and position tolerance.|
AutoCAD Spline Properties
Существует несколько типов сплайнов, но все они обладают аналогичными свойствами.
- The spline in AutoCAD is divided into segments (like polyline), which are called "nodes." If nodes (segments) are unevenly distributed along spline, then spline in AutoCAD is called non-uniform B-spline.
- To define shape of an AutoCAD spline, “defining points” and “control vertices” are used. defining points are by default on line of spline, and control vertices are outside it.
- Order of spline AutoCAD determines how many times its curvature can vary within one segment. curve of first order is straight line. curve of second order has constant curvature (arc). By default, spline in AutoCAD is combination of segments of 3-degree polynomial curves (also called "cubic curves" - they can have one curvature change per segment. Fourth-order curves - two changes, etc., you can bring its value to 10.
The Spline command is responsible for building spline in program. Call which you can (start building spline):
- You can create spline in AutoCAD from menu bar item Drawing - line Spline in drop-down list two lines with possibility to choose methods of construction: "AutoCline spline by defining points" and "control vertex spline".
- You can build an AutoCAD spline from Home tab of tool ribbon — in Drawing toolbar — two buttons with ability to choose how to build: “spline by defining points” and “autoline spline by control vertices”;
- You can also draw spline from classic Drawing toolbar - AutoCad Spline button;
- you can draw it, write name of command in command line "Spline".
Construction of spline on defining points
Call in AutoCAD Spline command from command line. command prompt will prompt:
The command line also displays current AutoCAD spline settings: "Method = Defining", "Nodes = Chord". We indicate its first defining point. By default, yellow dashed line is displayed, which will follow from first defining point to cross hairs cursor. program will request:
If you want to set touch at starting point of AutoCAD spline, then select Touch at beginning option, since after specifying second defining point, this option will be unavailable. We specify coordinates of second defining point of spline by clicking on drawing. program draws part of spline in AutoCAD, and also displays dashed yellow line that will follow from second defining point to crosshair cursor. system will display query:
Set next defining point of spline. program will display request:
After specifying third defining point, Close option appeared, which closes spline.
You can select Tolerance option, which allows you to change precision of stroke of defining points by spline (does not apply to extreme points). value of tolerance 0 builds spline curve in AutoCAD that runs exactly through all control points. tolerance value is greater than 0, builds spline curve, which runs in vicinity of control points within tolerance.
The Tangency at End option allows you to specify tangency condition at end point of spline.
To complete construction of spline in AutoCAD press "Enter".
How to build (make) spline in AutoCAD in various mathematical ways
Splines in program are built mathematically. Building spline by defining points contains option "Nodes", which allows you to select mathematical methods for constructing spline.
"Chord". (Method for determining chord length). placement of nodes connecting each component curve is proportional to distances between each associated pair of defining points.
"Square root". (Centripetal way). placement of nodes connecting each component curve is proportional to square root of distance between each associated pair of smoothing points. This method usually creates “softer” curves.
"Evenly". (Equal Intermediate Method). Places nodes for each component of curve at equal distances from each other, regardless of distance between smoothing points. This method often creates curves that extend defining points.
Building AutoCAD Spline on Control Vertices
Call command Spline, then select option "Method - HC / CV". command prompt will prompt:
We indicate first point of AutoCAD spline by clicking on drawing. By default, yellow dashed line is displayed, which will drag from first point to cross hairs cursor. system will prompt you:
That is, we need to specify coordinates of first control vertex of AutoCAD spline, since first point indicated is not. When using method of constructing spline along control vertices, first and end points of spline are specified by defining points. Set control vertex of spline in AutoCAD by clicking on drawing. As soon as we specify control vertex, sketch of spline will appear, which will stretch from first defining point to crosshair cursor. dashed yellow line will extend from control vertex to crosshair cursor. white dashed line appears that starts at first defining point of spline and passes through specified control vertex of spline to crosshair cursor. program will issue following request:
We indicate next control vertex of AutoCAD spline by clicking on drawing. dashed yellow line will stretch from last specified control vertex of spline to cross-hair cursor. dashed white line will begin at first defining point of spline and pass through specified control vertices to crosshair cursor. sketch of spline in AutoCAD will also stretch from first defining point to crosshair cursor.
Notice how spline is built in AutoCAD on control vertices (a special case). dashed white line connecting control vertices forms polyline. spline is inscribed in polyline and passes through end vertices of polyline, as well as through midpoints of intermediate links of polyline in event of spline bend in these sections.
The command prompt will prompt:
We indicate final defining point of spline by clicking on drawing. To complete AutoCAD Spline command, press "Enter".
How to convert polyline into AutoCAD spline
The Spline command in AutoCAD using "Object" option will allow you to convert two-dimensional or three-dimensional polyline into spline.
If you want to convert polyline to an AutoCAD spline without prior smoothing, then select option "Method - HC" (construction of spline along control vertices)
Converting polyline into AutoCAD spline by defining points without preliminary smoothing is impossible.
Useful lessons and related topics
I recommend to get acquainted with similar lessons on AutoCAD:
- how to combine splines in AutoCAD;
- How to turn spline into AutoCAD into polyline;
- broken line of segments;
- smooth curve spline;
- universal line polyline;
- multiline set.
Read and see also:
- how to draw objects;
- AutoCAD window (interface);
- customization of program interface.
Courses, tutorials AutoCAD:
- 2D design.
- 3D modeling.
- descriptive geometry.
- Engineering graphics.
- House plan.
- Assembly drawing of spur gear.
- 3D kitchen model.
Video "Construction in AutoCAD Splines (Bezier Curves)"