<s>
In	O
computer-aided	B-Application
design	I-Application
,	O
Geometric	B-Language
Description	I-Language
Language	I-Language
(	O
GDL	O
)	O
is	O
the	O
programming	O
language	O
of	O
Archicad	B-Application
library	O
parts	O
.	O
</s>
<s>
GSM	O
is	O
the	O
file	O
format	O
of	O
these	O
CAD	B-Application
objects	O
.	O
</s>
<s>
These	O
objects	O
are	O
similar	O
to	O
blocks	O
in	O
AutoCAD	B-Algorithm
,	O
but	O
unlike	O
blocks	O
,	O
these	O
are	O
parametric	O
,	O
and	O
the	O
2D	O
and	O
3D	O
features	O
are	O
connected	O
,	O
so	O
in	O
any	O
view	O
one	O
can	O
get	O
the	O
correct	O
visualization	O
(	O
for	O
example	O
a	O
side	O
view	O
on	O
the	O
section	O
,	O
top	O
view	O
on	O
plan	O
,	O
and	O
perspective	O
in	O
the	O
3D	O
view	O
)	O
.	O
</s>
<s>
GDL	O
scripts	O
define	O
an	O
Archicad	B-Application
library	O
part	O
in	O
its	O
main	O
roles	O
,	O
these	O
are	O
3D	O
model	O
,	O
3D	O
model	O
projected	O
to	O
section/elevation	O
or	O
to	O
2D	O
plan	O
,	O
2D	O
plan	O
view	O
,	O
user	B-Application
interface	I-Application
display	O
and	O
behaviour	O
and	O
listing	O
quantities	O
.	O
</s>
<s>
All	O
versions	O
of	O
the	O
Archicad	B-Application
contain	O
their	O
own	O
default	O
libraries	O
,	O
also	O
objects	O
like	O
furniture	O
,	O
windows	O
,	O
doors	O
,	O
trees	O
,	O
people	O
,	O
cars	O
,	O
construction	O
elements	O
,	O
etc	O
.	O
</s>
<s>
GDL	O
is	O
a	O
free	O
technology	O
(	O
although	O
Archicad	B-Application
itself	O
is	O
a	O
commercial	O
software	O
)	O
,	O
it	O
is	O
allowed	O
and	O
possible	O
to	O
develop	O
GDL	O
based	O
object	O
libraries	O
using	O
free	O
tools	O
like	O
Graphisoft	O
LP_XMLConverter	O
and	O
Graphisoft	O
GDL	O
Web	O
Plug-In	O
.	O
</s>
<s>
Every	O
movement	O
,	O
rotation	O
or	O
stretching	O
of	O
the	O
coordinate	O
system	O
is	O
called	O
a	O
transformation	B-Algorithm
.	O
</s>
<s>
Transformations	O
are	O
stored	O
in	O
a	O
stack	B-Application
,	O
which	O
can	O
be	O
extended	O
by	O
further	O
transformations	O
and	O
can	O
be	O
cut	O
by	O
deleting	O
one	O
or	O
more	O
transformations	O
from	O
the	O
top	O
of	O
it	O
.	O
</s>
<s>
GDL	O
maintains	O
forward	B-General_Concept
compatibility	I-General_Concept
,	O
which	O
means	O
that	O
an	O
Archicad	B-Application
library	O
part	O
will	O
be	O
readable	O
with	O
every	O
subsequent	O
Archicad	B-Application
program	O
,	O
but	O
not	O
necessarily	O
with	O
any	O
earlier	O
versions	O
.	O
</s>
