2002.03_2D Cad System Explored.pdf

FEATURE

VIRTUAL

DRAWING BOARD

For ambitious hobby

designers and

students QCad is a

good introduction to

the world of CAD.

Ulrich Wolf takes a

look at the

capabilities of this

free GPL CAD

program

not only extremely expensive but also so

complicated that they can hardly be operated

without some form of training. They offer a wide

variety of functions, many of which are only really

required by highly specialised professionals. QCad is

the exact opposite of such software packages: it’s a

2D CAD program with relatively few functions, but

those it has are well chosen and include all the most

important features.

QCad is included in almost every Linux distribution

and can also be downloaded from the program’s

Web site. The program is also available under

Windows as it uses the portable Qt-library. There is

however a royalty licence cost for the Windows

version.

rpm packages for dynamically linked libraries are

available – naturally the source code of the current

version is 1.4.7. If you still have Qt2.1 and don’t want

to go through a new compilation, you should install

the binaries of version 1.4.4 – the function range is

almost identical. An intensive revision and the leap to

QCad II are already planned.

QCad’s author, Andreas Mustun, also has a

commercial package. The program, called

QCad is a good introduction to CAD

CAMExpert, is currently available for the commercial

license fee of $160. It essentially extends QCad by

offering you the possibility of creating NC programs

for Computer Aided Manufacturing (CAM). It handles

formats such as Gerber, G-code and HP/GL. QCad

itself, however, reads and writes DXF files and

additionally exports in EPS. QCad does not have its

own proprietary format.

Those who are just finding their feet with CAD

have it relatively easy with Qcad. The operation is

self-explanatory and the interface is designed around

accustomed standards. One small difference is found

in the behaviour of the mouse: a right mouse click

does not, as is normal, call up a context menu but

instead concludes the current drawing operation. The

absence of scroll bars also takes a while to get used

to, though the Pan Zoom tool serves as a substitute

for this.

One very positive note is the existence of a helpful

user manual – something which is unfortunately not

always a matter of course with Free software –

though there are some points that are not described

in as much detail as we might like. There’s also no

find function to help you locate the information you

may need.

Whilst working, tool tips (or speech bubble help)

assist in finding the functions covered by each icon.

Qcad is also localised for numerous languages,

including Japanese. The manual is currently available

in English, French and German.

The program comes with a small library of

QCad includes a small library of DXF examples

LINUX MAGAZINE

Issue 18 • 2002

QCad – CAD in two dimensions

F or the most part, professional CAD systems are

FEATURE

prefabricated items such as screws, frames and even

a small Tux. The library is too small to be of any real

use, however. In order for it to be useful, you must

expand it with drawings created by yourself, – i.e.

normal DXF files – or procure DXF files of standard

parts from the manufacturer and integrate them into

the library path.

Even complex

drawings are

not a problem

for QCad.

Laying layers

As in all modern drawing and graphics programs,

Qcad lets you create different layers, also referred to

as folios. Graphic designers normally create a

different layer for each new object. For architects and

engineers however, it is sensible to divide up layers

according to functional criteria. For example one layer

might be used for the outlines, one for dimensions,

and separate layers for frames, text, help lines and so

on. This is also recommended, as QCad has no

separate function for help lines. It is practical to use

one pre-defined line colour for each layer. Layers can

be individually hidden and uncovered again; all

elements of a layer can be selected and edited as

one; and individual elements can be shifted from one

layer to another.

aspect was that the dimensions did not dynamically

adapt to subsequent drawing changes. This actually

seemed to be more a problem of the program from

which the file was exported than a failing of QCad.

When importing directly from Autocad or other

programs, the dimensions did adapt to changes, even

if they were on other layers.

One

great

feature is

that the

dimensions

are auto-

matically

changed

when

modifications

are made

to the

drawing

Weaknesses

95 per cent of the QCad code comes from the main

author Andreas Mustun. For this reason , the fact that

some functions are still missing is only too easy to

forgive. For example, there’s not yet a function that

allows the construction of ellipses – this must

currently be done using curves with defined reference

points. One option that is sorely missed is the ability

to group unconnected elements at will. The export

possibilities are also very limited. QCad can only

output files in the DXF and EPS formats. It’s worth

noting that all of these points are at the top of

Andreas Mustun’s To Do list.

Working to measure

QCad’s dimensioning function leaves nothing to

want: the units range from nanometers to light years,

thus permitting the construction of small galaxies,

should you wish. Diameters, radii and angles can be

easily provided with dimensions, as can imaginary

distances such as the distance between the centre

points of drill holes. One great feature, oft absent in

larger CAD packages, is that the dimensions are

automatically changed when modifications are made

to the drawing.

Although QCad is not a parameter-based CAD

program, it is nevertheless possible to stretch, squash

or distort closed forms. In order to actually receive

the desired results however, the operation’s so-called

point of reference must be selected very carefully. In

all operations, whether it is drawing or editing forms,

the multitude of supported “Snap Points” can prove

very helpful. The cursor thereby automatically snaps

to object or line intersections, centre points or similar

prominent points.

Summary

3D design is a matter of experience and requires

quite a different approach in planning to 2D design.

On the other hand, those who merely want to switch

from the drawing board or vector-based drawing

programs to CAD will have their wishes satisfied with

the free design environment of QCad.

The program is extremely stable, sufficiently fast

and can even handle larger files from foreign

programs without a problem. At first glance the

obvious lack of component libraries seems to be the

largest disadvantage. There are however many

manufacturers who make standard components of

their products, such as screws and profiles, available

as DXF files. This counteracts the problem of the

small library to some extent.

Since the program is totally limited to two

dimensions, it offers little help in the creation of

different views of an object. If the user wants to

implement complex projects, he or she should already

be familiar with the methods of a technical designer

or a draughtsman. The intuitive and easy to learn

operation however makes it possible to concentrate

fully on the construction of the project at hand.

The business of import/export

The author of QCad didn’t waste his time inventing

his own format, and one can therefore assume the

portable DXF format is sufficiently well supported. A

1.2 Mb file from an architect bureau caused only

slight problems: the characters in some fonts were

missing and the whole project, a very extensive

building, was scaled down to the size of a postage

stamp when opened. All the important information

was however preserved, including each of the ten

layers and their designations. The only unfortunate

Info

QCad and CAMExpert

homepage

http://www.ribbonsoft.com

Issue 18 • 2002

LINUX MAGAZINE

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