QCad User Reference Manual
|  |  | # 13 Object Snap This chapter lists all snap modes that can be activated to assist the user when setting points to exact co-ordinates. For most constructions and modifications in QCad, 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, QCad 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). Figure 20: The snap toolbar. ## Free Positioning CAD Toolbar: Menu: Snap - Free Hotkey: os Command: ? Description: 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. ## Snap to Grid CAD Toolbar: Menu: Snap - Grid Hotkey: sg Command: ? Description: Snaps to grid points. ## Snap to Endpoints CAD Toolbar: Menu: Snap - Endpoints Command: ? Hotkey: se Description: Snaps to endpoints of lines and arcs and to points (Figure 21). Figure 21: Endpoints found by the snap tool. ## Snap to Points on Entities CAD Toolbar: Menu: Snap - On Entity Hotkey: sn Command: ? Description: Snaps to the closest point that is on an entity (Figure 22). Figure 22: 'On Entity' snaps to any point on the line of an entity. ## Snap to Centers CAD Toolbar: Menu: Snap - Centers Hotkey: so Command: ? Description: Snaps to centers of lines and arcs and to points (Figure 23). Figure 23: Centers found by the snap tool. ## Snap to Middle Points CAD Toolbar: Menu: Snap - Middle Hotkey: sm Command: ? Description: 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. Figure 24: Middle points found by the snap tool. ## Snap to Distance Points CAD Toolbar: Menu: Snap - Distance from Endpoint Command: ? Options Toolbar: Description: Snaps to points with a given distance from endpoints (Figure 25). The distance can be adjusted in the options toolbar. Figure 25: Example snap points for the snap tool 'Distance from Endpoint'. ## Snap to Intersections CAD Toolbar: Menu: Snap - Intersection Hotkey: si Command: ? Description: Snaps to intersections between entities (Figure 26). Figure 26: The Intersection Snap tool finds automatically all visible intersection points. ## Snap to Intersections Manually CAD Toolbar: Menu: Snap - Intersection Manually Command: ? Description: 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). Figure 27: The Manual Intersection Snap tool also lets you specify invisible intersection points. ## Snap Restrictions In addition to the snap functions described above, QCad 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. 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. The mouse cursor is located at the circle line. Because QCad 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, QCad snaps to the point on the horizontal position of the relative zero point ("Snap Point"). Figure 28: Snap restrictions further limit the snap position to imaginary lines orthogonally to the relative zero point. ### Restrict Nothing CAD Toolbar: Menu: Snap - Restrict Nothing Command: ? Description: Disables all restrictions. ### Restrict Orthogonally CAD Toolbar: Menu: Snap - Restrict Orthogonally Command: ? Description: Restricts orthogonally to relative zero point. ### Restrict Horizontally CAD Toolbar: Menu: Snap - Restrict Horizontally Command: ? Description: Restricts horizontally to relative zero point. ### Restrict Vertically CAD Toolbar: Menu: Snap - Restrict Vertically Command: ? Description: Restricts vertically to relative zero point. ## Relative Zero Point As mentioned previously, there is a relative Zero point in every QCad 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. Normally, the relative zero point moves around automatically. For example if you're drawing a sequence of lines , 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. 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. ### Moving the Relative Zero Point CAD Toolbar: Menu: Snap - Set Relative Zero Command: ? Description: Lets the user set a new location for the relative zero point. ### (Un-)locking the Relative Zero Point CAD Toolbar: Menu: Snap - (Un-)Lock Relative Zero Command: ? Description: 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.
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