Day 2 – Specifying Points


Before you get very far with CAD in general and AutoCAD in particular, you will be confronted with prompts asking you to specify base, start, second, next, source, destination or closing points. Whether you’re using the LINE, PLINE, ARC, CIRCLE, ELLIPSE, SPLINE or other similar shape creation commands OR you’re editing exiting geometry using basic commands such as COPY, MOVE, STRETCH, ALIGN, etc. you will need to know how to specify points. The more methods you know the better equipped you will be to handle most problems or design challenges. Let’s take a quick but thorough review of most, if not all of the point construction or specification methods that AutoCAD provides. I will create the list in order of frequency and “popularity.”

1. Use a mouse click. This is arguably the easiest way to do it. You simply click somewhere in the drawing editor area, and AutoCAD figures out the coordinate of the location you clicked on. Beware that having SNAP turned on may change how this behaves, forcing the picked point to line on an imaginary grid as defined by the SNAP setting.

2. OSnap (F3). This is the most precise and simultaneously convenient way to specify points. It is precise because AutoCAD object snaps to particular strategic points or features on objects, such as the ENDpoint, MIDpoint, CENter, NODe, QUADrant, INTersection, EXTension, INSertion, PERpendicular, TANgent, NEAret, APParent Intersection, PARallel or NONe (to supress all of the previous object snaps). Technically, each of these constitutes an individual method to specify a point. When you let AutoCAD do the feature recognition work, this method is called AutoSNAP, because the program will automatically look for and recognize feature that you have enabled in the OSMODE System Variable or OSNAP settings.

OSnap (F3)

OSnap (F3) Options

3. Object Snap Override. This occurs when you actually type or select a specific object snap, instead of using the AutoSNAP method above.

4. @ = Last Point = Shift + 2 = Relative Coordinates. I use this method very frequently, perhaps even more frequently than the previous methods, but it requires some thinking. In my experience, this method gives me a great deal of control that the previous, more convenient methods, lack. This methods allows you to construct or specify a point based on a displacement relative to the last point, which AutoCAD abbreviates as the symbol @, which you read or speak of as “AT.” For example, to draw a rectangle that represents a common business card, you would type the following commands:

RECTANG

0,0

@3.5,2

5. Absolute Coordinates. When you know the exact coordinate location of a point, you can simply type it in.

6. The previous two methods each have multiple “sub-methods” you can use. For both absolute and relative coordinates you can specify points using Orthogonal or Cartesian coordinates, Polar coordinates and Spherical and Cylindrical Coordinates.

7. You can use F8 Ortho Mode to constrain the creation of the next point to being along a vertical or horizontal imaginary line drawn from the previous or last point.

8. Polar (F10) Polar Tracking to constrain the creation of the next point to being along imaginary lines drawn from arbitrary angles from the previous or last point.

9. OTrack (F11) Object Snap Tracking. This allows you to use imaginary vertical and horizontal lines that extend from points you “acquire” by letting the mouse cursor rest on enabled object snap points for a few moments.

10. TT Temporary Track Point.

11. From. This method allows you to create or specify a point as an offeset FROM another point.

If this isn’t enough for you, there’s more. You can use the ID, LIST, DBLIST and PROPERTIES palette to read coordinate points. I won’t assign this a method number because the information you get you use using methods 4 or 5, Relative and Absolute coordinates, respectively. However, if you think we’ve run out of methods, please hang on. There is more.

12. LISP. You can save an reuse point coordinate values easily by using a LISP expression such as:

(setq P1 (getpoint))

In response to the prompt you get, use one of your favorite command specification methods. The valule of the point’s coordinates will be saved in the P1 variable. You can later recall it at the command prompt by typing !P1, that is exclamation point followed by the variable name P1.

The methods listed here should take care of most of your point specification needs. If you know of other methods I failed or forgot to mention, please email me and I will add it here.

Object Snap Toolbar

Object Snap Toolbar

Enjoy using one of the richest programs available, when it comes to providing you with methods to specify points. You can access these methods from the command prompt area, a short-cut menu accessible via Shift + Right Mouse Click, the Object Snap toolbar and the AutoSnap feature.

Shift + Right Click

Shift + Right Click

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