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<center>LibreCAD User Reference Manual<br>
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<a name="Snapping"></a>
<a name="Object Snap"></a>
<a name="Entity Snap"></a>
<a name="13"></a><h1>13 Object Snap</h1>
<p>
<i>This chapter lists all snap modes that can be activated to assist
the user when setting points to exact co-ordinates.</i></p>
<p>
For most constructions and modifications in LibreCAD, it is necessary to
specify the co-ordinates of reference points, startpoints, endpoints, centers
or other identifying points. In order to make it possible to pick exact
positions defined by previously drawn entities or by the grid, LibreCAD offers
you a set of object snap modes. The toolbar that features those modes, is
automatically shown whenever it makes sense to use them (Figure
20).</p>
<p class="figure">
<a href="img/toolbar_snap.png"><img border="0" src="img/toolbar_snap_t.png"></a></p><p class="figure_label">
<b>Figure 20: </b>The snap
toolbar.</p>
<a name="Free Positioning"></a>
<a name="Snap - Free"></a>
<a name="13_1"></a><h2>Free Positioning</h2>
<p>
<b>CAD Toolbar:</b>
</p>
<p>
<img border="0" src="imgs/toolbar_snap_free.png"><br>
</p>
<p>
<b>Menu:</b>
</p>
<p class="code">
Snap - Free</p>
<p>
<b>Hotkey:</b>
</p>
<p class="code">
os</p>
<p>
<b>Command:</b>
</p>
<p class="code">
?</p>
<p>
<b>Description:</b>
</p>
<p>
Allows the user to set the co-ordinate freely using the mouse. Note,
that this is almost never the recommended way of setting co-ordinates in a
CAD system.</p>
<a name="Grid"></a>
<a name="Snap - Grid"></a>
<a name="13_2"></a><h2>Snap to Grid</h2>
<p>
<b>CAD Toolbar:</b>
</p>
<p>
<img border="0" src="imgs/toolbar_snap_grid.png"><br>
</p>
<p>
<b>Menu:</b>
</p>
<p class="code">
Snap - Grid</p>
<p>
<b>Hotkey:</b>
</p>
<p class="code">
sg</p>
<p>
<b>Command:</b>
</p>
<p class="code">
?</p>
<p>
<b>Description:</b>
</p>
<p>
Snaps to grid points.</p>
<a name="Endpoints"></a>
<a name="Snap - Endpoints"></a>
<a name="13_3"></a><h2>Snap to Endpoints</h2>
<p>
<b>CAD Toolbar:</b>
</p>
<p>
<img border="0" src="imgs/toolbar_snap_endpoint.png"><br>
</p>
<p>
<b>Menu:</b>
</p>
<p class="code">
Snap - Endpoints</p>
<p>
<b>Command:</b>
</p>
<p class="code">
?</p>
<p>
<b>Hotkey:</b>
</p>
<p class="code">
se</p>
<p>
<b>Description:</b>
</p>
<p>
Snaps to endpoints of lines and arcs and to points (Figure
21).</p>
<p class="figure">
<img border="0" src="imgs/snapendpoint.png"></p><p class="figure_label">
<b>Figure 21: </b>Endpoints
found by the snap tool.</p>
<a name="On Entity"></a>
<a name="Snap - On Entity"></a>
<a name="13_4"></a><h2>Snap to Points on Entities</h2>
<p>
<b>CAD Toolbar:</b>
</p>
<p>
<img border="0" src="imgs/toolbar_snap_onentity.png"><br>
</p>
<p>
<b>Menu:</b>
</p>
<p class="code">
Snap - On Entity</p>
<p>
<b>Hotkey:</b>
</p>
<p class="code">
sn</p>
<p>
<b>Command:</b>
</p>
<p class="code">
?</p>
<p>
<b>Description:</b>
</p>
<p>
Snaps to the closest point that is on an entity (Figure
22).</p>
<p class="figure">
<img border="0" src="imgs/snaponentity.png"></p><p class="figure_label">
<b>Figure 22: </b>'On Entity'
snaps to any point on the line of an entity.</p>
<a name="Centers"></a>
<a name="Snap - Centers"></a>
<a name="13_5"></a><h2>Snap to Centers</h2>
<p>
<b>CAD Toolbar:</b>
</p>
<p>
<img border="0" src="imgs/toolbar_snap_center.png"><br>
</p>
<p>
<b>Menu:</b>
</p>
<p class="code">
Snap - Centers</p>
<p>
<b>Hotkey:</b>
</p>
<p class="code">
so</p>
<p>
<b>Command:</b>
</p>
<p class="code">
?</p>
<p>
<b>Description:</b>
</p>
<p>
Snaps to centers of lines and arcs and to points (Figure
23).</p>
<p class="figure">
<img border="0" src="imgs/snapcenter.png"></p><p class="figure_label">
<b>Figure 23: </b>Centers found by
the snap tool.</p>
<a name="Middles"></a>
<a name="Snap - Middle"></a>
<a name="13_6"></a><h2>Snap to Middle Points</h2>
<p>
<b>CAD Toolbar:</b>
</p>
<p>
<img border="0" src="imgs/toolbar_snap_middle.png"><br>
</p>
<p>
<b>Menu:</b>
</p>
<p class="code">
Snap - Middle</p>
<p>
<b>Hotkey:</b>
</p>
<p class="code">
sm</p>
<p>
<b>Command:</b>
</p>
<p class="code">
?</p>
<p>
<b>Description:</b>
</p>
<p>
Snaps to middle points of lines and arcs and to points (Figure
24). Note that the middle point of an arc is in the middle of the
arc line while the center is at the center of the arc.</p>
<p class="figure">
<img border="0" src="imgs/snapmiddle.png"></p><p class="figure_label">
<b>Figure 24: </b>Middle points
found by the snap tool.</p>
<a name="Distance from Endpoint"></a>
<a name="Snap - Distance from Endpoint"></a>
<a name="13_7"></a><h2>Snap to Distance Points</h2>
<p>
<b>CAD Toolbar:</b>
</p>
<p>
<img border="0" src="imgs/toolbar_snap_dist.png"><br>
</p>
<p>
<b>Menu:</b>
</p>
<p class="code">
Snap - Distance from Endpoint</p>
<p>
<b>Command:</b>
</p>
<p class="code">
?</p>
<p>
<b>Options Toolbar:</b>
</p>
<p>
<img border="0" src="img/options_snap_dist.png"><br>
</p>
<p>
<b>Description:</b>
</p>
<p>
Snaps to points with a given distance from endpoints (Figure
25). The distance can be adjusted in the options toolbar.</p>
<p class="figure">
<img border="0" src="imgs/snapdist.png"></p><p class="figure_label">
<b>Figure 25: </b>Example snap points
for the snap tool 'Distance from Endpoint'.</p>
<a name="Intersection"></a>
<a name="Snap - Intersection"></a>
<a name="13_8"></a><h2>Snap to Intersections</h2>
<p>
<b>CAD Toolbar:</b>
</p>
<p>
<img border="0" src="imgs/toolbar_snap_intersa.png"><br>
</p>
<p>
<b>Menu:</b>
</p>
<p class="code">
Snap - Intersection</p>
<p>
<b>Hotkey:</b>
</p>
<p class="code">
si</p>
<p>
<b>Command:</b>
</p>
<p class="code">
?</p>
<p>
<b>Description:</b>
</p>
<p>
Snaps to intersections between entities (Figure
26).</p>
<p class="figure">
<img border="0" src="imgs/snapintersa.png"></p><p class="figure_label">
<b>Figure 26: </b>The Intersection
Snap tool finds automatically all visible intersection points.</p>
<a name="Intersection"></a>
<a name="Snap - Intersection Manually"></a>
<a name="13_9"></a><h2>Snap to Intersections Manually</h2>
<p>
<b>CAD Toolbar:</b>
</p>
<p>
<img border="0" src="imgs/toolbar_snap_intersm.png"><br>
</p>
<p>
<b>Menu:</b>
</p>
<p class="code">
Snap - Intersection Manually</p>
<p>
<b>Command:</b>
</p>
<p class="code">
?</p>
<p>
<b>Description:</b>
</p>
<p>
Sometimes the intersection snap mode cannot be used to snap to an
intersection point because the point is not on one or both of the entities.
The second intersection tool lets you specify the two entities and then snaps
the intersection point even if it's outside the entities (Figure
27).</p>
<p class="figure">
<img border="0" src="imgs/snapintersm.png"></p><p class="figure_label">
<b>Figure 27: </b>The Manual
Intersection Snap tool also lets you specify invisible intersection
points.</p>
<a name="13_10"></a><h2>Snap Restrictions</h2>
<p>
In addition to the snap functions described above, LibreCAD can further
restrict the position of the mouse cursor orthogonally to the position of the
relative zero point. Figure 28 illustrates an example of
how to use snap restrictions.
<br>
The 'Snap Point' is the point the user wants to specify. It's the point on
the bottom line of the shape that has the same X-co-ordinate like the center
of the full circle.
<br>
The mouse cursor is located at the circle line. Because LibreCAD is in the snap
mode "Snap to Center Points", the center of the circle would normally be the
snap point. A small rhombus highlights that point ("Center Point"). With the
snap restriction "Restrict Horizontally" activated, LibreCAD snaps to the point
on the horizontal position of the relative zero point ("Snap Point").</p>
<p class="figure">
<a href="img/snap_restriction01.png"><img border="0" src="img/snap_restriction01_t.png"></a></p><p class="figure_label">
<b>Figure 28: </b>
Snap restrictions further limit the snap position to imaginary lines
orthogonally to the relative zero point.</p>
<a name="Restrict Nothing"></a>
<a name="Snap - Restrict Nothing"></a>
<a name="13_10_1"></a><h3>Restrict Nothing</h3>
<p>
<b>CAD Toolbar:</b>
</p>
<p>
<img border="0" src="imgs/toolbar_snap_restrict_no.png"><br>
</p>
<p>
<b>Menu:</b>
</p>
<p class="code">
Snap - Restrict Nothing</p>
<p>
<b>Command:</b>
</p>
<p class="code">
?</p>
<p>
<b>Description:</b>
</p>
<p>
Disables all restrictions.</p>
<a name="Restrict Orthogonally"></a>
<a name="Snap - Restrict Orthogonally"></a>
<a name="13_10_2"></a><h3>Restrict Orthogonally</h3>
<p>
<b>CAD Toolbar:</b>
</p>
<p>
<img border="0" src="imgs/toolbar_snap_restrict_ortho.png"><br>
</p>
<p>
<b>Menu:</b>
</p>
<p class="code">
Snap - Restrict Orthogonally</p>
<p>
<b>Command:</b>
</p>
<p class="code">
?</p>
<p>
<b>Description:</b>
</p>
<p>
Restricts orthogonally to relative zero point.</p>
<a name="Restrict Horizontally"></a>
<a name="Snap - Restrict Horizontally"></a>
<a name="13_10_3"></a><h3>Restrict Horizontally</h3>
<p>
<b>CAD Toolbar:</b>
</p>
<p>
<img border="0" src="imgs/toolbar_snap_restrict_horizontal.png"><br>
</p>
<p>
<b>Menu:</b>
</p>
<p class="code">
Snap - Restrict Horizontally</p>
<p>
<b>Command:</b>
</p>
<p class="code">
?</p>
<p>
<b>Description:</b>
</p>
<p>
Restricts horizontally to relative zero point.</p>
<a name="Restrict Vertically"></a>
<a name="Snap - Restrict Vertically"></a>
<a name="13_10_4"></a><h3>Restrict Vertically</h3>
<p>
<b>CAD Toolbar:</b>
</p>
<p>
<img border="0" src="imgs/toolbar_snap_restrict_vertical.png"><br>
</p>
<p>
<b>Menu:</b>
</p>
<p class="code">
Snap - Restrict Vertically</p>
<p>
<b>Command:</b>
</p>
<p class="code">
?</p>
<p>
<b>Description:</b>
</p>
<p>
Restricts vertically to relative zero point.</p>
<a name="13_11"></a><h2>Relative Zero Point</h2>
<p>
As mentioned previously, there is a relative Zero point in every LibreCAD
drawing. It appears as a small red circle with a hair cross. The relative
zero point is the reference point for relative co-ordinates you enter in the
command line and for snapping restrictions.
<br>
Normally, the relative zero point moves around automatically. For example if
you're drawing a
<a href="construction.html#Sequence%20of%20Lines">sequence of lines</a>
, the relative zero point always moves to the last point you've set. The next
point of the sequence can then be defined in relative co-ordinates to the
last point.
<br>
Sometimes this is not convenient and you would rather want to set the
relative zero point to another position or lock its position so it stops
moving around automatically. The snap toolbar offers two tools that do
exactly this.</p>
<a name="Move Relative Zero"></a>
<a name="Relative Zero"></a>
<a name="Set Relative Zero"></a>
<a name="Snap - Relative
Zero"></a>
<a name="13_11_1"></a><h3>Moving the Relative Zero Point</h3>
<p>
<b>CAD Toolbar:</b>
</p>
<p>
<img border="0" src="imgs/toolbar_snap_relzero.png"><br>
</p>
<p>
<b>Menu:</b>
</p>
<p class="code">
Snap - Set Relative Zero</p>
<p>
<b>Command:</b>
</p>
<p class="code">
?</p>
<p>
<b>Description:</b>
</p>
<p>
Lets the user set a new location for the relative zero point.</p>
<a name="Lock Relative Zero"></a>
<a name="Relative Zero"></a>
<a name="Unlock Relative Zero"></a>
<a name="Snap - Lock
Relative Zero"></a>
<a name="13_11_2"></a><h3>(Un-)locking the Relative Zero Point</h3>
<p>
<b>CAD Toolbar:</b>
</p>
<p>
<img border="0" src="imgs/toolbar_snap_relzero_lock.png"><br>
</p>
<p>
<b>Menu:</b>
</p>
<p class="code">
Snap - (Un-)Lock Relative Zero</p>
<p>
<b>Command:</b>
</p>
<p class="code">
?</p>
<p>
<b>Description:</b>
</p>
<p>
When enabled, this switch locks the position of the relative zero point.
This means it doesn't move around automatically. You can still move it
manually using the tool described above.</p>
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