Last Update: August, 2010

CAD Glossary

This page defines some important words and expressions used in QCAD sources and documentation.

- A -

Attribute - The attributes of an Entity are its color, line width and line style. Layers can also have the same attributes.

- B -

Block - A Block is a group of Entities . A Block can be inserted into the same graphic more than once with different Attributes and different locations, scaling factors, angles, ...

Block Insert - See Insert.

Bulge - Measurement for the geometry of an arc segment in a polyline. The bulge is the tangent of 1/4 the included angle for an arc segment, made negative if the arc goes clockwise from the start point to the endpoint; a bulge of 0 indicates a straight segment, and a bulge of 1 is a semicircle. See also DXF Reference.

BYBLOCK - Special attribute value for colors, line types and line widths. If an Entity has Attributes set to this value, the Attribute will be taken from the Insert Entity the Entity resides in. Please note that Blocks actually don't have Attributes but Inserts have. So the name "BYBLOCK" might be misleading.

BYLAYER - Special Attribute value for colors, line types and line widths. If an Entity has Attributes set to this value, the Attribute will be taken from the Layer the Entity resides on.

- C -

Child Window - A document window that depends on another document window. This is typically a window showing a Block which is part of a drawing.

- D -

Document - A Drawing or a Block .

Document Window - A GUI window which shows a document .

Drawing - QCAD Document consisting of Entities, Layers and Blocks .

DXF - DXF^TM is the Drawing Exchange Format defined by Autodesk. See also DXF Reference.

- E -

ECS - Same as OCS .

Entity - An Entity is a graphical object. An object with a graphical representation.

Entity Data - The defining geometrical data of an Entity . This does not include Attributes such as color, line width, line style. E.g. for a line Entity the Entity data are the start- and the endpoint.

Extents - The outer boundaries of the drawing.

- F -

Freeze - Layers can be frozen which means they are temporarily invisible.

- G -

Grid - A pattern of dots displayed on the screen to guide you.

- I -

Insert - An Insert is an Entity that refers to a Block . An Insert acts like a pointer to a certain Block .

- L -

Layer - A Layer usually contains Entities of a similar nature or with the same Attributes . Layers allow the user to quickly change the Attributes of all Entities on them. Layers can be made invisible (see Freeze ).

Linetype - All Entities are drawn with particular Attributes . One of these Attributes is the Linetype. Examples for Linetypes: solid, center, dashed, etc.

- M -

Modify - A term used for changing / editing Entities .

- O -

OCS - Object Coordinate System (also known as ECS, Entity Coordinate System).

- S -

Solid - A filled polygon Entity with three or four corners.

Spline - Piecewise parametric polynomial curve. Splines are a representation of curves that are often used to approximate complex shapes through curve fitting and interactive curve design.

- U -

UCS - User Coordinate System.

- W -

WCS - World Coordinate System.