Although we have already reviewed several techniques to draw with precision different objects, in practice, as our drawing acquires complexity, the new objects are usually created and always located in relation to the already drawn. That is, the elements already existing in our drawing give us geometric references for new objects. Very often we can find, for example, that the next line emerges from the center of a circle, a certain vertex of a polygon or the midpoint of another line. For this reason, Autocad offers a powerful tool for easily signaling these points during the execution of drawing commands called Reference to objects.
The object reference is therefore a key method to take advantage of the geometric attributes of objects already drawn for the construction of new objects, as it serves to identify and use points such as the midpoint, the intersection of 2 lines or a tangent point among others. It can also be said that Object Reference is a transparent command type, that is, it can be invoked during the execution of a drawing command.
A quick way to take advantage of the different references to available objects is to use the button on the status bar, which allows you to activate specific references, and we insist, even though we have already started a drawing command. Let's take a preliminary look.
Let's look at an example. We will draw a straight line whose first end will match the vertex of a rectangle and the other with the quadrant to ninety degrees of a circle. In both cases we will activate the references to necessary objects during the execution of the drawing command.
The object reference allowed us to construct the line with all accuracy and without really worrying about the coordinates, angle or length of the object. Now suppose we want to add a circle to this piece whose center coincides with the existing circle (it is a metallic connector in a side view). Again, an Object Reference button will allow us to obtain this center without resorting to other parameters such as its absolute Cartesian coordinate.
References to objects that can be activated with the button and its appearance can be seen immediately.
In addition to the previous ones, we have some other references to objects in a context menu if, during a drawing command, we press the "Shift" key and then the right mouse button.
A peculiar characteristic of some of the references that appear in this menu is that they do not refer strictly to the geometric attributes of the objects, but to extensions or derivations of these. That is, some of these tools identify points that exist only under certain assumptions. For example, the reference "Extension", which we saw in an earlier video, shows, precisely, a vector that indicates the sense that would have a line or an arc if they were more extensive. The reference "Fictional Intersection" can identify a point that does not really exist in three-dimensional space as we also saw in video.
Another example is the reference "Medium between 2 points", which, as its name indicates, serves to establish the midpoint between any two points, although that point does not belong to any object.
A third case that works in the same sense, that is to say, to establish points that derive from the geometry of the objects but do not belong to them precisely, is the reference "From", that allows to define a point at a distance of Another base point. So this "object reference" can also be used in combination with other references, such as "End Point".
In previous versions of Autocad, it was very common to activate the toolbar "References to objects" and go pressing the buttons of the desired references in the middle of a drawing command. This practice can still be done, although the appearance of the interface ribbon tends to clear the drawing area and decrease the use of toolbars. Instead, you can now use the drop-down button on the status bar, as illustrated above. However, Autocad also offers a method to automatically activate one or more references to be used permanently when drawing. To do this we must configure the behavior of the "Object reference" with the corresponding eyebrow of the "Drawing parameters" dialog box.
If in this dialog we activate, for example, the references "End point" and "Center", then those will be the references that we will see automatically when we start a drawing or editing command. If at that moment we want to use another reference, we can still use the button of the status bar or the contextual menu. The difference is that the contextual menu will only activate the desired object reference temporarily, while the dialog box or the status bar button leaves them active for the following drawing commands. However, it is not advisable to activate all references to objects in the dialog box, even less if our drawing contains a large number of elements, since the number of points indicated can be so great that the effectiveness of the references can be lost. Although it should be noted that when there are many points of references to active objects, we can place the cursor at a point on the screen and then press the "TAB" key. This will force Autocad to show the references near the cursor at that moment. Conversely, there may be times when we want to deactivate all references to automatic objects to, for example, have full freedom with the cursor on the screen. For those cases, we can use the "None" option in the contextual menu that appears with the "Shift" key and the right mouse button.
On the other hand, it is evident that Autocad points out an end point, for example, in a different way than a mid-point indicates and this in turn is clearly distinguished from a center. Each reference point has a specific marker. Whether these markers appear or not, as well as whether the cursor is "attracted" to that point, is determined by the configuration of AutoSnap, which is nothing more than the visual aid of the "Reference to objects". To configure AutoSnap, we use the "Drawing" tab of the "Options" dialog box that appears with the Autocad start menu.