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*The graPHIGS Programming Interface : Subroutine Reference*

## GPELA3 - Elliptical Arc 3

**GPELA3
(***center*,
*refv1*,
*refv1*,
*startv*,
*endv*) |

**Purpose**

Use
**GPELA3** to insert an Elliptical Arc 3
structure element into the open structure following the
element pointer or to replace the element pointed at by the
element pointer with an Elliptical Arc 3 structure element
depending on the current edit mode.
This is the fully specified, three-dimensional form
of the elliptical arc primitive.

The major and minor axis
(*refv1* and
*refv2* respectively) parameters define a
parallelogram that circumscribes the ellipse and is anchored
at the center of the ellipse
(*center*)
Two sides are parallel to the major axis.
The other two sides are parallel to the minor axis.
The major and minor axes extend from the center of the
ellipse to midpoints of sides of the parallelogram.
The ellipse is tangent to the sides of the parallelogram at
their midpoints.

The elliptical arc is defined parametrically as the image
of an arc of the unit circle in a two-dimensional
parameter space.
The major and minor axes are images of unit parameter vectors
in the
*x* and
*y* directions respectively.
The graPHIGS API draws the elliptical from the starting angle to
the end angle through increasing parameter values.

Polyline attributes are applied to this primitive.

**GPELA3** is identified as GDP 1010.

**Note: **

Not all GDPs are supported on all workstations.
Use the Inquire List of Generalized Drawing Primitives
(**GPQGD**)
subroutine
to determine the GDPs supported by an opened workstation.
See also the workstation description in
The graPHIGS Programming Interface: Technical Reference

**Parameters**

*center* -- specified by user,
3 short floating-point numbers (MC)
Center of arc.
*refv1* -- specified by user,
3 short floating-point numbers (MC)
Major axis of ellipse.
This direction vector is anchored at the center of the ellipse.
*refv2* -- specified by user,
3 short floating-point numbers (MC)
Minor axis of ellipse.
This direction vector is anchored at the center of the ellipse.
*startv* -- specified by user,
short floating-point number
Start value for creation of arc
(specified in radians)
*endv* -- specified by user,
short floating-point number
End value for creation of arc
(specified in radians)
**Error Codes**

**5**
- FUNCTION REQUIRES STATE STOP OR NROP (NOT STCL)
**107**
- REFERENCE VECTORS ARE COLINEAR

**Related Subroutines**

**GPLT**
- Set Linetype
**GPLWSC**
- Set Linewidth Scale Factor
**GPPLCD**
- Set Polyline Color Direct
**GPPLCI**
- Set Polyline Color Index
**GPPLET**
- Set Polyline End Type
**GPPLI**
- Set Polyline Index

**RCP code**

201328151
(X'0C000617')

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