Lesson18- Object Snap Overrides



An Osnap (short for Object SNAP) lets you snap onto geometric positions of objects when AutoCAD prompts you to pick a point.

  • this lets you draw objects precisely without having to determine (or even know) the required coordinates.
  • osnaps are one of the most important drafting tools to learn.

One way to use an osnap is to type the first 3 letters (abbreviation) 
of the desired osnap mode when AutoCAD prompts for a point.

For example, suppose you wanted to draw a LINE segment between 
P1 and P2 using the precise end points of these existing LINEs.

You could start the Line command and then type END at the prompt for a starting point to invoke an Endpoint osnap.

  • then you would hold your crosshairs over the desired end point and wait for the Endpoint tooltip and marker to appear.Command: _line
    Specify first point: END ↵ 
    of (move your crosshairs over the desired end point)

When the Endpoint marker and tooltip appear you can press your left mouse button to use the point at the marker.

  • the Line command would continue and you could repeat the procedure to acquire the end point for the other end of the LINE.

You can also invoke osnap overrides from the Object Snap toolbar or the Standard toolbar flyout when AutoCAD prompts for points

  • or you can press & hold the <shift> key and right-click in the drawing area to invoke a shortcut menu of osnaps instead.

Object snaps are affected by several settings that can be changed from the Drafting tab of Options.

  • these settings (saved in the registry) include the AutoSnap Marker Size, the Aperture Size and AutoSnap Settings.

The Marker displays the current object snap location when your crosshairs move over a snap point of an object.

  • you can adjust the marker size to suit your preferences (and your screen resolution) with the AutoSnap Marker Size slider.

When Magnet is checked your crosshairs jump to osnap points if they are near your crosshairs (inside the Marker).

When Display AutoSnap Tooltip is checked the currently selected object snap is displayed in a tooltip.

Display AutoSnap aperture box is normally not checked so you do not see the current Aperture Size on-screen.

  • the aperture box (centered on your crosshairs) determines how close your crosshairs must be to an object to use an osnap.
  • you can experiment with different Aperture Size settings to find an appropriate aperture size for your drawings.The AutoSnap marker color is Yellow by default which will be obvious on a Black screen background (the default).
  • you should use a color that is more obvious (e.g. Blue) if you change your background screen color to White.

There are many different object snap modes and add-on applications can introduce custom object snaps as well.

  • you will be using different object snaps throughout the course so do not worry about mastering all osnap modes right now.
  • if you would like to learn more about a particular osnap mode you can use the built-in AutoCAD Help feature.

Practice using object snap overrides

1- Continue with the drawing you created in the previous exercise. (if you did not complete the previous exercise you can Open T104_1.dwg in your personal folder).

2- Pick Draw + Line and when prompted for the first point press and hold the <shift> key and right-click in the drawing area to invoke a shortcut menu. Select Endpoint.

3- Hold your crosshairs over the point shown below and wait for the marker and tooltip to appear. Then press your left mouse button to use this point.

4- Type END at the prompt for the next point to invoke another Endpoint osnap override. Hold your crosshairs over the point shown below and wait for the marker and tooltip to appear then press your left mouse button to use this point.

Specify next point or [Undo]: END

You created a new LINE that precisely connects two other LINE objects at their end points

  • and you did not even have to know what the coordinates for these end points were to create this LINE.5- Complete the remaining LINE objects using an Endpoint osnap override for each point.
    When you return to the starting point press <enter> to complete the Line command.

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