How to Use Dynamic UCS

Quick answer: With Dynamic UCS (DUCS) on, the coordinate system automatically aligns to whatever entity or face is under your cursor while you draw, then reverts to your regular WCS or UCS once the command finishes. Toggle it with F6 or the DUCS field in the Status Bar, and it’s recommended to turn UCSFOLLOW off while using it.

What Dynamic UCS Does

Rather than manually redefining your coordinate system to match a face you want to draw on, Dynamic UCS detects the entity or face under your cursor and aligns automatically, for the duration of the current command only.

Which Entity Types Are Supported

UCSDETECT controls this:

1. Faces of 3D solids, surfaces, subdivision meshes, and regions, this is the default.
2. A wider range of other entity types: point, line, polyline, 2D polyline, 3D polyline, ray, xline, arc, circle, ellipse, spline, text, mtext, solid, 3Dface, trace, block insert, viewport, mline, leader, mleader, hatch, helix, camera, light, section, shape, PDF underlay, and image.

Right-click the DUCS field in the Status Bar to choose which types are supported. Entities inside blocks can be selected too, except curved faces of ACIS entities within non-uniformly scaled blocks.

Toggling Dynamic UCS

Press F6, or click the DUCS field in the Status Bar.

Using Dynamic UCS

1. With Dynamic UCS active, launch an entity creation command, LINE, for example.
2. Move the cursor over an entity or 3D solid face. It highlights; if GRIDMODE is on, the grid aligns with whatever’s hovered too.
3. If UCSICON is set to 3 (On at Origin), the UCS icon displays. Its orientation depends on exactly how the cursor touches the entity or face, giving you a way to control the DUCS orientation yourself. On 3D solid faces, the origin sits at the starting point of the solid edge, with the X-axis running co-directional to the tangent at that starting point. On curved faces specifically, the X-axis is tangent to the face, the Y-axis lies within the face, and the Z-axis is perpendicular to it.
4. Optionally tap Shift to lock the DUCS in place, letting you draw outside the hovered entity or face; tap Shift again to unlock it.
5. Execute the entity creation command. If bitcode 2 of OSOPTIONS is set, entity snaps ignore negative Z-values in the current UCS during this step.
6. Once the command finishes, your regular coordinate system (WCS or UCS) is automatically restored.

Locked-Face Highlight Appearance

Two preferences control how a locked face looks once you’ve held Shift to lock the DUCS to it:

• RedHilite_DUCSLocked_Face_Color: the highlight colour.
• RedHilite_DUCSLocked_Face_Alpha: the highlight transparency.

Frequently Asked Questions

Does Dynamic UCS permanently change my coordinate system? No. It aligns automatically for the duration of the current command only, then your regular WCS or UCS is restored once the command finishes.

How do I draw outside the entity or face I’m hovering over with Dynamic UCS active? Tap Shift to lock the DUCS in place first, then you can draw beyond that entity or face’s boundaries. Tap Shift again to unlock it.

What determines the DUCS orientation on a curved face? The X-axis is tangent to the face, the Y-axis lies within the face, and the Z-axis is perpendicular to it, and exactly how the cursor touches the face when you hover lets you influence that orientation.

Can Dynamic UCS detect entities other than 3D solid faces? Yes, but by default UCSDETECT only covers faces of 3D solids, surfaces, subdivision meshes, and regions. A much wider range of other entity types is also available; right-click the DUCS field in the Status Bar to choose.