Reference and Constraints with AutoCAD - Section 3

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.