__IGES File Format Specification: Section P__

#### P (Parameter) Section

The P section contains all the data for all the geometric entities within the IGES file.Here we are going to look at some of this data mainly relevant to surfacing systems. For full details refer to the US-PRO IGES specification.

The fields here are comma delimited. The first field for any entity is the entity number. The last 8 characters on each line are always the line numbers within the P section e.g. "P 22" is the 22nd line within P. In the numbering of the fields below we do not include the first field (the entity number) or the line number field ("P 22" for instance). This is the numbering system adopted in the US Pro standard document.

##### Entity Type 100: Circular Arc

(see USPRO PDF file page 94)For example:

100,18.07701962,8.56055349,-6.890174421,18.56055349, 25P 22

-6.890174421,8.56055349,3.109825579,0,0; 25P 23

Field 1: ZT displacement of arc from XT, YT plane

Field 2: X1 arc centre abscissa (x value)

Field 3: Y1 arc centre ordinate (y value)

Field 4: X2 start point abscissa

Field 5: Y2 start point ordinate

Field 6: X3 end point abscissa

Field 7: X3 end point ordinate

Field 8 etc: pointers as required

Arcs are defined in the definition space coordinate system XT, YT, ZT. In order to transform these coordinates to model space we need to apply a transformation to them:

R x Xin + T = Xout

Where:

R is a 3x3 rotation matrix

T is a 3x1 translation vector

The transformation matrix is defined in the IGES file as a type 124 entity (see below). The relevant transformation matrix to use for any given entity is specified in field 7 of the directory (D) section.

##### Entity Type 102: Composite Curve

(see USPRO PDF file page 96)For example:

102,4,31,33,35,37,0,0; 39P 44

Field | Description |
---|---|

1 | N, Number of entities |

2 | Pointer to the DE of the first constituent entity |

1+N | Pointer to the DE of the last constituent entity |

The constituent entities allowed include points, connect points and parameterised curves. Points are included so that properties or notes can be added at the start or end points of any curves within the composite curve.

##### Entity Type 106, forms 11-13: Linear Path Entity

(see USPRO PDF file page 123)For example:

106,2,6,-57.03032303,0.,43.56941986,-23.333498,0.,59.09231186, 19P 13

-2.078577995,0.,56.60169983,21.33639526,0.,47.97143173, 19P 14

30.92703056,0.,39.10948181,37.83919907,0.,28.79950142,0,0; 19P 15

The second field defines the type (or form) of the entity. The form numbers can be 11, 12 or 13 corresponding to values of 1,2 and 3 in the second field. In this case the field value is 2 so therefore the entity is of form 12. This is the case of a series of 3D points in model space. The format of the fields is therefore:

Field 1: Type (form) of entity

Field 2: N, the number of 3D coordinates (>=2)

Field 3: X1

Field 4: Y1

Field 5: Z1

.... Field 2+3*N: ZN

Note that other forms are possible (field 1) and this will affect the contents of the following fields. Refer to the US Pro IGES document for details. There may be additional pointer fields following this.

##### Entity Type 116: Point

(see USPRO PDF file page 131)For example:

116,4747.868164,0.,1276.950806,0,0,0; 19P 13

Fields 1-3: X, Y, Z coordinate values of the point

Field 4: Defines the symbol used. If zero, then no symbol has been specified

##### Entity Type 124: Transformation Matrix Entity

(see USPRO PDF file page 37) For example:124,0.8421788659,-0.3763897044,-0.3860900893,0.,-0.4167362674, 19P 13

-0.7075399544E-8,-0.9090274325,0.,0.342148566,0.9264614349, 19P 14

-0.1568552511,0.,0,0; 19P 15

A transformation of a geometric entity is defined by a rotation matrix R (3x3) and a translation vector T (3x1) as follows:

R x Xin + T = Xout

where Xin is the coordinate vector of the object in its definition space and Xout is the coordinate vector of the object in model space.

##### Rotation Matrix R

R11 | R12 | R13 |

R21 | R22 | R23 |

R31 | R32 | R33 |

##### Xin vector

XIN | YIN | ZIN |

##### Translation vector, T

TX | TY | TZ |

TX, TY and TZ are translations in the X, Y and Z directions.

##### Xin vector

XIN | YIN | ZIN |

In the P section:

Field 1-3: R11-13 (rotation matrix top row)

Field 4: T1 (translation vector top element)

Field 5-7: R21-23

Field 8: T2

Field 9-11: R31-33

Field 12: T3

##### Entity Type 126: Rational B-Spline Curve Entity

(see USPRO PDF file page 152)For example:

126,11,11,0,0,1,0,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,0.,1.,1.,1., 31P 201 1.,1.,1.,1.,1.,1.,1.,1.,1.,1.,1.,1.,1.,1.,1.,1.,1.,1.,1.,1.,1., 31P 202 -81.95101929,0.,-76.2480011,-63.77590526,0.,-71.65812978, 31P 203 -65.3942337,0.,-38.11034393,-20.08093643,0.,-34.02118683, 31P 204 -9.250563188,0.,-57.88851582,8.924550837,0.,-53.2986445, 31P 205 24.85890007,0.,-72.65955353,55.48272324,0.,-66.31718445, 31P 206 74.90270996,0.,-47.54043961,91.70846558,0.,-10.23730755, 31P 207 99.80012096,0.,-30.3492879,117.975235,0.,-25.75941658,0.,1.,0., 31P 208 0.,0.,0,0; 31P 209

Field | Description |
---|---|

1 | K, upper index of sum |

2 | M, degree of basis functions |

3 | 0=nonplanar, 1=planar |

4 | 0=open curve, 1=closed curve |

5 | 0=rational, 1=polynomial |

6 | 0 = nonperiodic, 1 = periodic |

7 | First knot value |

7+A | Last knot value |

8+A | First weight |

8+A+K | Last weight |

9+A+K | X(0), first control point |

10+A+K | Y(0) |

11+A+K | Z(0) |

9+A+4*K | X(K), last control point |

10+A+4*K | Y(K) |

11+A+4*K | Z(K) |

12+A+4*K | Starting parameter value |

13+A+4*K | Ending parameter value |

14+A+4*K | X(norm), unit normal |

15+A+4*K | Y(norm) |

16+A+4*K | Z(norm) |

##### Entity Type 128: Rational B-Spline Surface

(see USPRO PDF file page 155)For example:

128,5,2,3,2,0,0,1,0,0,0.,0.,0.,0.,0.5,0.5,1.,1.,1.,1.,0.,0.,0., 21P 14 1.,1.,1.,1.,1.,1.,1.,1.,1.,1.,1.,1.,1.,1.,1.,1.,1.,1.,1.,1.,1., 21P 15 0.,0.,0.,16.66666667,0.,3.921529071,33.33333333,0.,6.805883602, 21P 16 66.66666667,0.,7.042270256,83.33333333,0.,4.316467322,100.,0., 21P 17 0.,0.,50.,3.898397838,16.66666667,50.,7.819926909,33.33333333, 21P 18 50.,10.70428144,66.66666667,50.,10.94066809,83.33333333,50., 21P 19 8.21486516,100.,50.,3.898397838,0.,100.,0.,16.66666667,100., 21P 20 3.921529071,33.33333333,100.,6.805883602,66.66666667,100., 21P 21 7.042270256,83.33333333,100.,4.316467322,100.,100.,0.,0.,1.,0., 21P 22 1.,0,1,19; 21P 23

Field | Description |
---|---|

1 | K1, Upper index of first sum |

2 | K2, Upper index of second sum |

3 | M1, Degree of first set of basis functions |

4 | M2, Degree of second set of basis functions |

5 | 1=closed in 1st parametric direction, 0=not closed |

6 | 1=closed in 2nd parametric direction, 0=not closed |

7 | 0=rational, 1=polynomial |

8 | 0=non-periodic in 1st parametric direction, 1=periodic |

9 | 0=non-periodic in 2nd parametric direction, 1=periodic |

10 | S(-M1), 1st value of 1st knot sequence |

.. | .. |

10+A | S(N1+M1), last value of 1st knot sequence |

11+A | T(-M2), 1st value of 2nd knot sequence |

.. | .. |

11+A+B | T(N2+M2), last value of 2nd knot sequence |

12+A+B | W(0,0), first weight |

13+A+B | W(1,0) |

.. | .. |

11+A+B+C | W(K1,K2), last weight |

12+A+B+C | X(0,0), 1st control point |

13+A+B+C | Y(0,0) |

14+A+B+C | Z(0,0) |

15+A+B+C | X(1,0) |

16+A+B+C | Y(1,0) |

17+A+B+C | Z(1,0) |

.. | .. |

9+A+B+4*C | X(K1,K2), last control point |

10+A+B+4*C | Y(K1,K2) |

11+A+B+4*C | Z(K1,K2) |

12+A+B+4*C | U(0), start value for 1st parametric direction |

13+A+B+4*C | U(1), last value for 1st parametric direction |

14+A+B+4*C | V(0), start value for 1st parametric direction |

15+A+B+4*C | V(1), last value for 1st parametric direction |

.. | Additional pointers as required |

where:

N1 = 1+K1-M1

N2 = 1+K2-M2

A = N1+2*M1

B = N2+2*M2

C = (1+K1)*(1+K2)

##### Entity Type 142: Curve on a Parametric Surface

(see USPRO PDF file page 191)For example:

142,0,19,29,39,1,0,0; 41P 45

Field | Description |
---|---|

1 | Indicates the way that the curve was created |

2 | Pointer to the DE of the surface on which the curve lies |

3 | Pointer to the DE of the entity that defines the curve B in u,v space |

4 | Pointer to the DE of the curve C |

5 | Indicates the preferred representation in the sending system |

Field 1 indicates how the curve was created:

0 = unspecified

1 = projection of a curve onto surface

2 = intersection of 2 surfaces

3 = iso-parametric curve

Field 5 indicates the preferred representation in the sending system:

0 = unspecified

1 = S o B is preferred

2 = C is preferred

3 = equal preference

##### Entity Type 144: Trimmed (Parametric) Surface

(see USPRO PDF file page 195)For example:

144,19,1,0,41,0,1,43; 45P 47

Field | Description |
---|---|

1 | Pointer to DE (directory entry) of the surface to be trimmed |

2 | N1 = 0 if the outer boundary is not trimmed, N1 = 1 otherwise |

3 | N2 is the number of inner closed boundaries |

4 | Pointer to the DE of the curve (type 142) defining the outer boundary, if any. Zero otherwise. |

5 | Pointer to the DE of the first closed inner boundary curve |

4+N2 | Pointer to the DE of the last closed inner boundary curve |

##### Entity Type 406: Property Entity

(see USPRO PDF file page 444)For example:

406,1,9HMaterial1; 43P 46

The property entity contains alphanumeric data which may be referenced by other entities.

Field | Description |
---|---|

1 | NP, number of property values |

2 | 1st property value |

.. | .. |

1+NP | Last property value |

In the above example the property entity has been used to store the surface colour (material) from ICEM Surf.