1. Computer Aided Engineering Drawing
Basic Concepts of AutoCAD
Chapter No 2
Sir Syed University of Engineering & Technology
Computer Engineering Department
University Road, Karachi-75300, PAKISTAN

2. Text Book Text Book: Mastering AUTOCAD 14 By George Omura
Course Outline is available at CAED course website.

3. Chapter Outline Coordinate System Limit Command Unit Command
GRID and SNAP Command
ORTHO Command
OSNAP Command
ZOOM Command
REDRAW and REGEN Command
PAN Command
HIGHLIGHT Command

4. Co-ordinate System in AutoCAD
AutoCAD’s drawing environment is based on the Cartesian coordinate system
The horizontal axis is called the X-axis and the vertical axis is called the Y-axis. The plane that contains these axes is called the X-Y Plane.
The X-axis and The Y-axis intersect at a single point, called the origin. Equidistant points, called the coordinates are placed along these axes.

5. 3 Ways to Enter Values
Absolute System
Relative System
Polar System

6. Co-ordinate System in AutoCAD
Absolute System: X, Y
Absolute System represents the absolute real values of the drawing limits.
For example 3,3 to 8,3 will draw a line from the position vector of 3,3 to the position vector of 8,3.
You can specify a point by typing its X, Y and Z values separated by the commas.
Example: Command: line
From point: 3.5,4.5,5.5

7. Co-ordinate System in AutoCAD
Relative X, delta Y
Relative System represents the relative position of X and Y coordinates of the new points compared to the previous points.
For example line from 3,3 will draw a line from the position vector of 3,3 to the position that is 5 units away from the previous points in the positive X-axis direction.

8. Co-ordinate System in AutoCAD
Relative X, delta Y
You can specify a point as an offset from the last point you entered, simply type before the rest of the specification.
For instance last point = 10,6,4

9. Co-ordinate System in AutoCAD
Polar < Angle
Similar to the relative addressing, this system makes use of the distance and the direction angle of the new point away from the previous point.
For example, line from 3,3 < 0; will draw a line from the position vector of 3,3 to the position that is 5 units away from the previous points in the zero degree direction.

10. Co-ordinate System in AutoCAD
Polar < Angle
You can specify a point by entering its distance from the current UCS origin and its angle in the XY plane separated by the sign <. 90
< 45
< 180
270

11. LIMITS Command
Before beginning a new drawing, it is very important that you define the drawing boundaries for the current drawing.
The LIMITS command lets you change the upper and lower limits of the drawing area while working on a drawing, and to turn limits checking on or off.
The current drawing area has a length of 12 units and a breadth of 9 units, by default.

12. LIMITS Command Format: LIMITS
ON/OFF/ <Lower left corner> <current>:
Upper right corner< ,9.0000>:
Options
ON Enables limits checking, retaining the current values of the limits themselves. While limits checking are enabled, AutoCAD rejects attempts to enter points outside the drawing limits (although an entity, such as a Circle, might start within the limits and extend outside them). Also governs the limits of the visible grid.
OFF Disables limits checking, but remembers the values of the limits for the next time the check is enabled.

13. UNITS Command
The UNITS command governs the display and input formats for coordinates, distances, and angles. The UNITS command doesn't compromise the accuracy of calculations, only the way that numbers are displayed and input to a drawing.
Format: UNITS
When you enter the UNITS command, AutoCAD prompts you to make the following selections:

14. UNITS Command Display/input formats for coordinates and distances:
Scientific 1.55E+01 (15.5 drawing units)
Decimal "
Engineering 1'-3.50" "
Architectural 1'-3 1/2" "
Fractional 15 ½ "

15. DDRMODES -- Drawing Aids Dialogue Box
The DDRMODES command lets you control the settings of various drawing aids, such as Snap and Grid by using dialogue boxes. Dialogue boxes work only with certain display drivers.
Format: DDRMODES
When you issue the DDRMODES command, AutoCAD displays the Drawing Aids dialogue box, allowing you to control on-screen drawing aids.
It subsumes all of the functions of the ORTHO, FILL (Solid Fill), QTEXT (Quick text), BLIPMODE (Blips), HIGHLIGHT, SNAP, GRID, and ISOPLANE commands.

16. DDRMODES -- Drawing Aids Dialogue Box
Options
Snap Spacing
Sets alignment spacing.
ON Aligns designated points.
OFF Does not align designated points.
Aspect Sets different X/Y snap resolution.
Rotate Rotates snap grid by specified angle, and sets a specified base point for the grid.
Style Sets Snap style to either Isometric or Standard.

17. GRID Command
The GRID command controls the display of a grid of alignment dots to help you place objects in drawings.
Format: GRID
Grid spacing (X) or ON/OFF/Snap/Aspect <current>:
Note: You can also turn GRID on and off using the F7 key or CTRL+G.

18. GRID Command Options Grid Spacing (X)
A simple number sets grid spacing in drawing units. A number followed by "X" (e.g., "2X") sets the grid spacing to a multiple of the current snap resolution. A value of zero locks the grid spacing to the current snap resolution. ON
Turns grid on with previous spacing.
OFF
Turns grid off.
Aspect
Permits a grid with different horizontal and vertical spacing.

19. SNAP Command
The SNAP command lets you control the snap resolution, the spacing of an imaginary grid of dots with which newly designated points must align. You can alter the resolution or turn it off entirely for freestyle drawing.
Format: SNAP
Snap spacing or ON/OFF/Aspect/Rotate/Style <current>:
Note: Snap can be turned on and off with the
F9 key or CTRL+B

20. ORTHO Command
The ORTHO command lets you control orthogonal drawing mode.
When orthogonal mode, also known as "ortho" mode, is set to ON, movement within the drawing is constrained to the vertical and horizontal axes, as these are defined in the current Snap grid.
Format: ORTHO
OFF/ON <current>:

21. ORTHO Command Options Note:
ON Turns orthogonal mode on.
OFF Turns orthogonal mode off.
Note:
When the Snap grid is rotated, Ortho mode rotates accordingly. Also, if the isometric snap style is in effect, Ortho mode is applied to the axis pair associated with the current isometric plane.
Note: ORTHO can be turned on and off with the F8 key or Ctrl + O.

22. OSNAP Command
Object Snap defines the way in which you can snap to those drawings that are already completed.
The OSNAP command is used to set "running" object snap modes from the Command line. (DDOSNAP sets them using a dialogue box).
Object snap lets you designate points that are related to objects already in your drawing.
Format: OSNAP
Object snap modes:

23. OSNAP Command Options CENter Center of Arc or Circle
ENDpoint Closest endpoint of Line/Arc or closest corner of Trace/Solid/3D Face
INSertion Insertion point of Text/Block/Shape/Attribute
INTersection Intersection of Lines/Arcs/Circles or corner of Trace/Solid/3D Face
MIDpoint Midpoint of Line/Arc or midpoint of an edge of Trace/Solid/3D Face
NEArest Nearest point on Line/Arc/Circle/Point
PERpendicular Perpendicular to Line/Arc/Circle
TANgent Tangent to Arc or Circle

24. ZOOM Command
The ZOOM command magnifies or shrinks the drawing on the display screen.
Format: ZOOM
All/Center/Dynamic/Extents/Left/Previous/Vmax/ Window/<Scale(X/XP)>:

25. ZOOM Command Options All Displays entire drawing (all visible layers).
Center Specifies center point and new display magnification.
Dynamic Permits you to pan a box representing the viewing screen around the entire generated portion of the drawing and enlarge or shrink it in a dynamic, graphic manner.
Extents Displays current drawing content as large as possible.
Vmax Zooms out as far as possible without forcing a regeneration.
Window Designates rectangular area to be drawn as large as possible.

26. BLIPMODE Command
The BLIPMODE command controls the generation of marker "blips" -- the small temporary marks drawn whenever you designate a point.
Format: BLIPMODE
ON/OFF <current>:
Command Options
ON Blips are drawn.
OFF Blips are suppressed.

27. REDRAW Command
The REDRAW command redraws the current viewport, causing it to appear opaque over viewport behind it. REDRAW also eliminates any point entry blips from the display.
Format: REDRAW
You can use the REDRAWALL command to redraw all active viewports. Both commands can be used Transparently as 'REDRAW and 'REDRAWALL.
Viewport is the bounded area that displays some portion of the drawing model space.

28. REDRAWALL Command
The REDRAWALL command redraws all viewports, eliminating all point entry blips from each viewport.
Format: REDRAWALL
The REDRAW command can be used to redraw the current viewport only, causing it to appear opaque over viewports behind it.
Both commands can be used transparently as 'REDRAW and 'REDRAWALL.

29. REGEN Command
The REGEN command regenerates the drawing in the current viewport by recalculating all the entities in the drawing database, and redrawing the screen.
Format: REGEN
Regeneration occurs automatically when you change the display of your drawing with some ZOOM or PAN operations. It also occurs in the HIDE and SHADE commands.
The REGENALL and REGENAUTO commands have further control over regenerations.

30. REGENAUTO Command
Some commands can change many entities at once. The drawing must be regenerated to reflect such a change, so some commands perform this regeneration automatically.
The REGENAUTO command lets you control whether automatic regenerations are performed on a drawing.
Format: REGENAUTO

31. REGENAUTO Command ON/OFF <current>:
If REGENAUTO is set to OFF, and a ZOOM or PAN needs to regenerate the drawing, AutoCAD prompts:
About to regen, proceed? <Y>
If you respond with N, the PAN or ZOOM is aborted. This prompt does not appear if input is coming from a menu item or a script.

32. PAN Command
The PAN command lets you move the display window in any direction, without changing its magnification.
It has the same effect as using the scroll bars. This lets you see details that are currently off screen.
You can specify a relative movement, as in:
Format: PAN
Displacement: Enter relative coordinates.
Second point: Press.

33. PAN Command
Or you can designate two points to specify the displacement you want.
Format: PAN
Displacement: Indicate a point.
Second point: Indicate a point.

34. HIGHLIGHT Command
HIGHLIGHT is a system variable that determines whether entities will be displayed as dashed objects when object selection is in progress. The value stored is an integer.
Options
0 Entities will not be highlighted during object selection.
1 Entities will be highlighted during object selection.

35. Getting Out of Trouble from AutoCAD
Backspace <  >
Whenever you make a typing error you can use the backspace key to delete up to the error.
Cancel < Ctrl + C >
After executing a command, if you have decided not to continue with that command then presses the key: Ctrl+C for canceling a command.
Alternatively, you can also click at the AutoCAD found at the top right corner.

36. Getting Out of Trouble from AutoCAD
Escape < ESC >
If you want to quickly exit from a dialog box without making any changes, then you can press the ESC key.
Undo < U >
If you have accidentally change something in the drawing and you want to reverse back the change, then you can press the U key at the command prompt.
Redo
If you have accidentally undo one too many commands, you can redo (undo the undo) the last commands by entering the command REDO. Redo restores only one command.