Arc

An Arc is a portion of a circle defined by a center, radius, start angle, and sweep angle. In bridge drawings you'll use it for fillets between intersecting members, return arcs on parapet ends, curved abutment wingwall outlines, drilled-shaft outlines, and any place where you need a true circular sweep rather than a polyline approximation.

To draw: pick the center, then the start point (which sets the radius and start angle), then a final point (which sets the sweep angle).

Geometry

Name: Identifier within the parent CAD document. Must be unique.

Level: The layer controlling color, line weight, and dash style.

Center X / Center Y: Coordinates of the arc's center.

Radius: Distance from the center to the arc.

Start Angle: Angle (in degrees) where the arc begins, measured counter-clockwise from the horizontal axis.

Arc Angle: Sweep — total angle the arc covers from start to end. Positive values sweep counter-clockwise, negative clockwise.

Start X / Start Y / End X / End Y: Endpoint coordinates (read-only — derived from center, radius, and angles).

Editing

Move the center: drag the center handle to translate.

Resize: drag any of the four quadrant handles to change the radius. Center stays fixed.

Adjust the sweep: drag either endpoint handle to change the start angle or sweep angle while keeping the radius fixed.

Snap: other shapes can snap to the center, the start, the end, and the midpoint of the arc.

Notes

For full circles use a Circle, not an Arc with sweep 360°.

For very flat arcs (sweep angle below ~5°) the result is nearly indistinguishable from a straight line at typical drawing scales — use a Line instead unless the arc is drawn at large scale and the curvature matters visually.

When the parent CAD document is alignment-driven, the arc's center is placed onto the alignment, but the arc itself stays a true circular arc (it does not warp into an elliptical curve over a horizontal curve).