AutoCAD Advantages

In this edition of AutoCAD Advantages, we thought it would be helpful to share some basic glossary terms to help better your understanding of AutoCAD.

Coordinates

X,Y,Z values indicating a cartesian coordinate system for placing all objects. Most of the time Z=0. Basically, this is a grid system for describing location. There is a defined origin (0,0). The unit measurements are also defined (inches, mm, cm, etc.). Coordinates are indicated with the horizontal value (X) first, then the vertical (Y).

Units

Base unit of measurement. Everything is expressed in terms of this measurement. There’s a bit of complexity involved with this information – Architectural, Decimal, Engineering, Surveying Mm, cm, m, inches, feet, yards. The file has to know what kind of units it uses, and what kind of units other drawings are coming in at, and unit conversions have to take place, for instance, 1inch = 2.54cm.

Extents

The rectangle that contains all the visible information in the drawing. The extents of this drawing is shown by the blue dotted box. If you were to zoom to the extents, all the lines and points would be visible. The system variables EXTMAX and EXTMIN refer to the upper left point and the lower left point of the rectangle.

Layers

The organizational system for drawings. All items on a layer share certain properties and can be turned on and off as a group. This is often explained as a bunch of layers of tracing paper on top of each other. I find that explanation a bit simplistic. Layers are used for controlling visibility and line thickness as well as organization. On/Off vs. Thawed/Frozen – On/Off layers are loaded into memory, so they can be quickly toggled. Thawed/Frozen require a drawing refresh (the difference was a HUGE deal back in the day – there was a significant trade off with performance – not so noticeable now).

Blocks

Containers of geometry. Allows the program to use shorthand when dealing with multiple instances. It isn’t 20 do-hickeys, it is 1 do-hickey referenced 20 times. These could also be considered internal references (as opposed to external references), or a file within a file. There’s a presentation, here that I’ve used to explain blocks and Xrefs. I’d be happy to review it at some point. When inserted the program mostly only cares about: Insertion point (insPoint) the X,Y,Z coordinates of the block Scale factors (X,Y,Z) these can all be adjusted separately, but usually aren’t Rotation – a number generally expressed in degrees

X-refs

External References. Allows an autoCAD drawing to contain another AutoCAD drawing. Originally this was used to make working with a file much faster. The current file doesn’t allow you to edit the information in the reference. Now it is used to allow mutlitple people to work on a single drawing. It is also useful for organization. I think of this as a pointer from one file to another. There’s a presentation, here that I’ve used to explain blocks and Xrefs.

  • Nested X-ref – A file contained within a file.
  • Attached – firm connection to the drawing, passed through if this drawing is Xrefed into another drawing
  • Overlayed – file just sits on top – not passed along if containing file is xrefed into another drawing.

Model Space

Where the drawing takes place. 3D is available. Everything is drawn 1:1.

Paper Space


A print preview. Only 2D available. Viewports into Model Space, show areas at scale. You can have two areas at different scale (close and far) at the same time.

Grid

A rigid coordinate system where only certain values are acceptable for snapping purposes. See coordinate system.

Purge

Removes unused entities. (They exist in the drawing definitions but aren’t visible.)

Colors

There are a couple color spaces that you may have to deal with: RGB (millions of colors) , and AutoCAD colors (256 colors) This is similar to the web based color palette, but not exactly the same.

RGB

Red Green Blue – Color Space for mixing light. Also expressed as a coordinate system R,G,B.

AutoLISP

One of several programming languages in AutoCAD. Based on, but different from, Common LISP. Here is a good online resource here.


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