Editing IGES (section)

==File format==
An IGES file is composed of 80-character [[ASCII]] records, a record length derived from the [[punched card]] era. Text strings are represented in "[[Hollerith constant|Hollerith]]" format, the number of characters in the string, followed by the letter "H", followed by the text string, ''e.g.'', "4HSLOT" (this is the text string format used in early versions of the [[Fortran]] language). Early IGES translators had problems with [[IBM]] [[mainframe computer]]s because the mainframes used [[EBCDIC]] encoding for text, and some EBCDIC-ASCII translators would either substitute the wrong character, or improperly set the [[parity bit]], causing a misread.

Here is a very small IGES file from 1987,<ref>{{cite web |url=http://www.wiz-worx.com/iges5x/misc/slot.shtml |title=MISC - IGES Example File slot |access-date=2010-01-08 |archive-url=https://web.archive.org/web/20100815044620/http://www.wiz-worx.com/iges5x/misc/slot.shtml |archive-date=2010-08-15 |url-status=dead }}</ref> containing only two POINT (Type 116), two CIRCULAR ARC (Type 100), and two LINE (Type 110) entities. It represents a slot, with the points at the centers of the two half-circles that form the ends of the slot, and the two lines that form the sides.

<pre>
                                                                        S      1
1H,,1H;,4HSLOT,37H$1$DUA2:[IGESLIB.BDRAFT.B2I]SLOT.IGS;,                G      1
17HBravo3 BravoDRAFT,31HBravo3->IGES V3.002 (02-Oct-87),32,38,6,38,15,  G      2
4HSLOT,1.,1,4HINCH,8,0.08,13H871006.192927,1.E-06,6.,                   G      3
31HD. A. Harrod, Tel. 313/995-6333,24HAPPLICON - Ann Arbor, MI,4,0;     G      4
     116       1       0       1       0       0       0       0       1D      1
     116       1       5       1       0                               0D      2
     116       2       0       1       0       0       0       0       1D      3
     116       1       5       1       0                               0D      4
     100       3       0       1       0       0       0       0       1D      5
     100       1       2       1       0                               0D      6
     100       4       0       1       0       0       0       0       1D      7
     100       1       2       1       0                               0D      8
     110       5       0       1       0       0       0       0       1D      9
     110       1       3       1       0                               0D     10
     110       6       0       1       0       0       0       0       1D     11
     110       1       3       1       0                               0D     12
116,0.,0.,0.,0,0,0;                                                    1P      1
116,5.,0.,0.,0,0,0;                                                    3P      2
100,0.,0.,0.,0.,1.,0.,-1.,0,0;                                         5P      3
100,0.,5.,0.,5.,-1.,5.,1.,0,0;                                         7P      4
110,0.,-1.,0.,5.,-1.,0.,0,0;                                           9P      5
110,0.,1.,0.,5.,1.,0.,0,0;                                            11P      6
S      1G      4D     12P      6                                        T      1
</pre>The file is divided into 5 sections: '''S'''tart, '''G'''lobal, '''D'''irectory Entry, '''P'''arameter Data, and '''T'''erminate indicated by the characters S, G, D, P, or T in column 73. The characteristics and geometric information for an entity is split between two sections; one in a two record, fixed-length format (the Directory Entry, or DE Section), the other in a multiple record, comma delimited format (the Parameter Data, or PD Section), as can be seen in a more human-readable representation of the file.<ref>{{cite web |url=http://www.wiz-worx.com/iges5x/misc/peek/slot.txt |title=MISC - IGES Example File slot (dump) |access-date=2010-08-16 |archive-url=https://web.archive.org/web/20120926172932/http://www.wiz-worx.com/iges5x/misc/peek/slot.txt |archive-date=2012-09-26 |url-status=dead }}</ref>

When displayed, the user should see two [[yellow]] points (hard to see on a [[white]] background, but most CAD systems use a [[black]] background), one located at the [[Origin (mathematics)|origin]] of model space [0,0,0], two [[red]] circular arcs, and two [[green]] lines.

[[File:slot.gif|center]]