UCS in AutoCAD

UCS sets the user coordinate system: an origin and X and Y axes anywhere in space, so its XY plane can tilt. The coordinates you type are read in it, and what you draw lies in its XY plane: with the origin moved to a box's top, a circle centred at 30,20 lies on the top. It first says the current UCS's name — *WORLD*, *NO NAME* or the name it was saved under — then asks for the new origin or an option; Enter there goes back to World. A point is the origin, with its Z, and a point without a Z lies at the current elevation. Then a point on the positive X axis and a point on the XY plane, read in the current UCS: Enter at either keeps the axes as they are. One point moves the UCS; three turn it any way.

The commands then work in the UCS's XY plane: LINE and CIRCLE draw on it, and BOX and EXTRUDE rise from it along its Z. Every object keeps its own plane when the UCS changes, and PLAN looks straight down on the current UCS. The UCS is saved in the drawing, and each run is one undo step. MellowCAD's 3D is solids only, and still partial.

• Command: UCS
• Panel: Inquiry & view
• Try it: Open the editor, type UCS and press Enter.

At the command line

The engine draws it and writes its history as you would type it: the prompts in AutoCAD 2027's order, with the same option letters.

Options

Face (F)

Listed as AutoCAD 2027 lists it, to align the UCS with a face of a solid. MellowCAD asks for the face, but does not align to one yet: every pick finds none.

NAmed (NA)

Saved UCSs, by name. Save stores the current one, asking Yes or No before it replaces a name already saved; Restore makes a saved one current, its name typed in any case; Delete takes names, with commas and wildcards; ? lists them, each with its origin and axes. A name holds spaces, but not <>/\":;|,=*? or a backquote: Invalid UCS name..

OBject (OB)

Aligns the UCS with an object you pick: a line, circle, arc, ellipse, polyline, spline, text, multiline text, attribute definition or block reference. The origin and the X axis go where AutoCAD puts them for each kind, and the Z is the object's own normal, so the UCS lies in the object's plane. An object on a locked layer can be picked. A hatch says This object does not define a coordinate system, and UCS ends with the UCS as it was.

Previous (P)

Goes back to the UCS before, up to ten back in a session, named ones and orthographic ones among them. With none left: No previous coordinate system saved..

View (V)

Turns the XY plane square to your line of sight, X along the screen's horizontal, keeping the origin: text drawn after it reads flat on the screen of a 3D view.

World (W)

Back to the world coordinate system, which never moves. It is the first prompt's default, so Enter there chooses it, and it sets the elevation back to 0 too.

X

Turns the UCS about its X axis: 90 degrees by default, an angle typed, or a point that gives it. A positive angle turns it by the right-hand rule, so 90 stands the XY plane up on the old X axis.

Y

Turns the UCS about its Y axis, as X does about X.

Z

Turns the UCS about its Z axis, as X does about X: 30 turns X and Y 30 degrees counter-clockwise, seen from above.

ZAxis (ZA)

A new origin, Enter keeping the current one, then a point on the positive Z axis: the XY plane stands square to it, its X kept level with the world's XY plane. Two points that are one say Points are coincident. Its Object takes a line, an arc, an open polyline or a spline: the origin at the end nearest the pick, Z along it pointing away.

What it does not do yet

Face, which aligns the UCS with a solid's face: it asks for one but finds none yet. Apply and SEction, listed at the first prompt and refused here, since there is one viewport and there are no section objects. The UCS dialog (UCSMAN), the icon's grips and its right-click menu, and the icon showing the new UCS while you place it. The crosshair turning with the UCS: it stays upright on screen until PLAN lines the view up with it. UCSFOLLOW, UCSVP and the dynamic UCS. OBject on a dimension, and Group at its pick. The depth an orthographic UCS keeps. The pause, Press ENTER to continue, in a long list.

What it does and still lacks, in detail (in English)

Questions

How do I reset the UCS to World in AutoCAD?

Run UCS and press Enter: World is the default. To look straight down on the drawing again, run PLAN and choose World.

How do I rotate the UCS?

Run UCS, choose Z and type the angle: 30 turns X and Y 30 degrees counter-clockwise. X and Y tilt the XY plane up, 90 degrees by default.

What is the difference between the UCS and the WCS?

The world coordinate system (WCS) never moves; the user coordinate system (UCS) is the one you move and turn. At the start they are the same, and UCS says the current one is *WORLD*. Coordinates you type are read in the UCS, and what you draw lies in its XY plane.

How do I draw on a face of a 3D solid?

Move the UCS onto it. On a box's top, its origin alone is enough: UCS, then a corner of the top, then Enter, as the session does. For a side, give three points: the origin at a corner, a point along an edge for X, and one more on the face for Y. Then draw: what you draw lies on the face.

Related commands

• PLAN in AutoCAD
• 3DORBIT in AutoCAD
• BOX in AutoCAD
• EXTRUDE in AutoCAD