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<title>Ipe Manual -- 6.3 Angular snapping</title>
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<table width="100%" cellpadding=0 cellspacing=2><tr><td bgcolor="#99ccff"><a href="manual_26.html"><img border="0" alt="6.4 Interaction of the snapping modes" src="next.png"></a></td><td bgcolor="#99ccff"><a href="manual_22.html"><img border="0" alt="6 Snapping" src="up.png"></a></td><td bgcolor="#99ccff"><a href="manual_24.html"><img border="0" alt="6.2 Context snapping" src="previous.png"></a></td><td align="center" bgcolor="#99ccff" width="100%"><b>6.3 Angular snapping</b></td></tr></table>
<h2>6.3 Angular snapping</h2>
When <em>angular snapping</em> is enabled, the mouse position is
restricted to lie on a set of lines through the <em>origin</em> of your
current <em>axis system</em>. The lines are the lines whose angle with
the <em>base direction</em> is an integer multiple of the snap
angle. The snap angle can be set in the second box in the Snap
toolbar. The values are indicated in degrees.
<p>For a snap angle of 180 degrees, snapping is to a single line through
the current origin.
<p><a name="id1">
In</A> order to use angular snapping, it is important to set the axis
system correctly. To set the origin, move the mouse to the correct
position, and press the <kbd>F1</kbd>-key. Note that angular snapping is
<em>disabled</em> while setting the origin. This way you can set a new
origin for angular snapping without leaving the mode first. Once the
origin has been set, the base direction is set by moving to a point on
the desired base line, and pressing the <kbd>F2</kbd>-key. Again, angular
snapping is disabled. Together, origin and base direction determine
the current <em>axis system</em>. Remember that the origin is also used
as the fix-point of scale, stretch, and rotate operations, if it is
set.
<p>You can un-set the current axis system by pressing
<kbd>Shift-F1</kbd>. This also turns off angular snapping.
You can set origin and base direction at the same time by pressing
<kbd>F3</kbd> when the mouse is very near (or snapped to) an edge of a
polygonal object. The origin is set to an endpoint of the edge, and
the base direction is aligned with it. This is useful to make objects
parallel to a given edge.
<p><p><a name="id2">
For</A> drawing rectilinear or c-oriented polygons, the origin should be
set to the previous vertex at every step. This can be done by pressing
<kbd>F1</kbd> every time you click the left mouse button, but that would
not be very convenient. Therefore, Ipe offers a second angular snap
mode, called <em>automatic angular snapping</em>. This mode uses an
independent origin, which is automatically set every time you add a
vertex when creating a polygonal object. Note that while the origin is
independent of the origin set by <kbd>F1</kbd>, the base direction and the
snap angle used by automatic angular snapping is the same as for
angular snapping. Hence, you can align the axis system with some edge
of your drawing using <kbd>F3</kbd>, and then use automatic angular
snapping to draw a new object that is parallel or orthogonal to this
edge.
<p>This snapping mode has another advantage: It remains silent and
ineffective until you start creating a polygonal object. So, even with
automatic angular snapping already turned on, you can still freely
place the first point of a polygon, and then the remaining vertices
will be properly aligned to make a <i>c</i>-oriented polygon.
<p>The automatic angular snapping mode is never active for any
non-polygonal object. In particular, to <em>move</em> an object in a
prescribed direction, you have to use normal angular snapping.
<p>A final note: Many things that can be done with angular snapping can
also be done by drawing auxiliary lines and using context snapping. It
is mostly a matter of taste and exercise to figure out which mode
suits you best.
<hr />
<table width="100%" cellpadding=0 cellspacing=2><tr><td bgcolor="#99ccff"><a href="manual_26.html"><img border="0" alt="6.4 Interaction of the snapping modes" src="next.png"></a></td><td bgcolor="#99ccff"><a href="manual_22.html"><img border="0" alt="6 Snapping" src="up.png"></a></td><td bgcolor="#99ccff"><a href="manual_24.html"><img border="0" alt="6.2 Context snapping" src="previous.png"></a></td><td align="center" bgcolor="#99ccff" width="100%"><b>6.3 Angular snapping</b></td></tr></table></body></html>
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