GEOMETRY LINE ARC [lnam] pstart pend pcentre [paxis] [divn]

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GEOMETRY LINE ARC [lnam] pstart pend pcentre [paxis] [divn]

This command is used to define an arc of less than 180 degrees via three points
or an ellipse via four points.

lnam	=	name of the line, used for later references to the line.
pstart	=	name of a point which defines the start point of the arc.
pend	=	name of a point which defines the end point of the arc.
pcentre	=	name of a point which is the centre of the arc.
paxis	=	name of the point which defines one axis of an ellipse. This point can be one
		of the end points of the ellipse. Generally the shortest part of an ellipse will
		be created; however, in situations where neither end point lies along the axis
		defined by 'pcentre' to 'paxis', the direction of the axis can be used to control
		which part of the ellipse is created. In order to achieve this, the axis (or an
		extension of the axis) should intersect the projected arc. This is illustrated in
		the examples below. In general, the segment of the ellipse that is defined may
		be toggled by reversing the direction of the axis.
divn	=	integer which specifies how many nodes are to be placed along the line. If
		omitted a default of four divisions (ie Five nodes) is assumed. The default
		number of divisions can be reset using the command
		MESHING DIVISION DEFAULT.

Notes:

1.: Deletion of the centre point
If the centre is deleted for any reason then the line will be changed to a straight line.
2.: Unequal radii
If the distance between the start point and centre point and the end point and centre point of a three point arc definition is not the same then a curve with a radius which varies linearly with angle will be created.
3.: Ambiguous ellipses
In situations where the ellipse definition is ambiguous or invalid a straight line is generated.

Return Level: GEOMETRY LINE

Examples:

1.

GEOMETRY LINE ARC C1 P1 P2 P3

Defines a line named C1 from P1 to P2 with centre P3.

**Figure 2.72:** Definition of an arc
$\begin{figure} \centerline{ \psfig {figure=diagrams/arc1.eps,height=1.0in} }\end{figure}$

2.

GEOMETRY LINE ARC ELL1 P2 P7 P1 P3

Defines an ellipse named ELL1 from P2 to P7 with a centre at P1 and one of the axes defined by P3.

**Figure 2.73:** Definition of an ellipse
$\begin{figure} \centerline{ \psfig {figure=diagrams/arc2.eps,height=1.0in} }\end{figure}$

3.

GEOMETRY LINE ARC ELL2 P2 P7 P1 P3

Defines an ellipse named ELL2 from P2 to P7 with a centre at P1 and one of the axes defined by P3.

**Figure 2.74:** Alternative definition of an ellipse
$\begin{figure} \centerline{ \psfig {figure=diagrams/arc3.eps,height=1.0in} }\end{figure}$

See also the following commands

'LABEL GEOMETRY LINES'
'UTILITY DELETE LINES'
'UTILITY TABULATE GEOMETRY LINES'
'VIEW GEOMETRY'

Next: GEOMETRY LINE CIRCLE pnam radius [plane] Up: GEOMETRY LINE Control Previous: GEOMETRY LINE ANGLE [new_l] old_l angle

Femsys Limited
1st October 1999