How Linetypes Behave on Arcs, Circles, Ellipses, and Splines
AutoCAD places linetype elements along an object’s path length. On a straight line this is easy to predict. On arcs, circles, ellipses, and splines, changing curvature affects spacing, orientation, and the available room for text or SHX symbols.
A curved linetype is not necessarily defective because its screen appearance differs from a straight test line. It must be evaluated against the geometry and the intended plotted scale.
How AutoCAD Maps a Linetype Along a Curve
The pattern advances along measured curve distance rather than across a straight chord. Dashes and gaps follow the tangent direction as the curve changes. Simple patterns tolerate this well; complex labels and symbols have a fixed visual size and can overlap when the radius becomes tight.
Linetypes on Arcs
Pattern Direction
An arc has a start point, end point, and direction. Relative text and shape rotation follows the local tangent, so reversing or recreating the arc can change the apparent orientation of complex elements.
Start and End Behavior
Endpoint fitting leaves drawn portions at the ends where possible. The middle cycles may be shortened or shifted compared with a long straight sample.
Short Arcs
A short arc can fail to show a gap or label for the same reason as a short line. Use the pattern-length diagnostic before assuming that curvature is the only cause.
Linetypes on Circles
Pattern Distribution Around a Closed Object
A circle has no visible endpoint, but its circumference still has a stored parameterization and a seam. The pattern repeats around the full circumference and must reconcile at that location.
The Pattern Meeting Point
If the circumference is not an exact multiple of the effective pattern cycle, the meeting region can contain an uneven dash or gap. Rotate or recreate the circle only when the seam’s position matters visually.
Small-Radius Circles
Large text or symbols can collide with neighboring cycles or extend across the circle. A simple dashed pattern, a smaller complex variant, or a block may be more appropriate.
Linetypes on Ellipses
Changes Along Curvature
An ellipse changes radius continuously. The pattern follows actual curve distance, but the viewer perceives elements differently near flatter and tighter portions.
Apparent Pattern Distortion
SHX shapes and text do not bend to match the ellipse. They are placed and rotated along the tangent, so equal symbols can appear crowded near the ends and widely separated along flatter sides.
Linetypes on Splines
Pattern Placement Along the Spline Length
The sequence follows the evaluated spline path. Editing fit points or control vertices changes that path length and can move every later label or symbol.
Tight Curves and Control Points
Sharp local curvature can rotate adjacent elements rapidly. Simplify unnecessary control points or use a less complex pattern for presentation.
Display Performance
Long splines with dense complex linetypes require more display calculation than simple lines. If navigation becomes slow, test a simpler representation or convert only approved deliverables.
Linetypes on Polyline Arc Segments
Mixed Straight and Curved Segments
A polyline can combine straight and arc segments while remaining one object. Pattern continuity depends on the object’s Linetype generation property.
Linetype Generation at Vertices
With generation disabled, each straight or curved segment restarts the sequence. With it enabled, the pattern advances across vertices. See PLINEGEN and polyline vertices for the exact distinction.
Complex Linetype Text on Curves
Text Rotation
The R parameter keeps the label relative to the path and can turn it upside down on reversed geometry. The U parameter attempts to keep it readable from the drawing’s upright direction.
Upright Text Behavior
Upright orientation is usually preferred for utility labels, but it does not guarantee perfect placement at every tangent. Test both drawing directions and read the complete R-versus-U orientation guide.
Overlap on Tight Curves
Increase blank spacing, reduce text size, or use a simpler code when labels overlap. Moving text away from the baseline with Y offset can help, but it also exaggerates displacement on small radii.
SHX Shapes on Curves
SHX symbols remain rigid while their insertion direction follows the path. Large arrows, triangles, or utility symbols can intersect the base line or one another. Test the symbol origin, scale, X/Y offsets, and rotation parameters from the complex-code reference.
Why Curved Linetypes May Look Uneven
- The object length does not contain a whole number of cycles.
- Curvature changes the visual spacing between rigid symbols.
- Endpoint or closed-object fitting modifies the terminal pattern.
- Polyline vertices restart the pattern when generation is disabled.
- Text and symbols are too large for the local radius.
- Display regeneration or tessellation makes screen zoom misleading.
Improve Linetype Readability on Curves
Adjust the Pattern Design
Use shorter dashes, more blank space around labels, smaller symbols, and an origin centered on the base path. Preserve a separate straight-line master if the curved variant requires different proportions.
Use a Simpler Pattern
Replace complex text or shapes with a simple dash-gap line in dense or small-radius areas, and identify the feature with a leader or legend.
Split Difficult Geometry
Where drafting rules permit, split the curve at a less visible point and control each section. Avoid fragmenting design geometry merely to improve decoration.
Curve Testing Procedure for Custom Linetypes
- Draw a long line as the reference sample.
- Create arcs with large, medium, and small radii.
- Create a circle, ellipse, spline, and mixed polyline.
- Test both original and reversed directions where supported.
- Test R and U text rotation separately.
- Inspect model space, layouts, plot preview, and PDF.
- Record the minimum acceptable radius and object length in the library documentation.