Reference and Constraints with AutoCAD - Section 3

A peculiar characteristic of some of the references that appear in this menu is that they do not strictly refer to the geometric attributes of the objects, but to extensions or derivations of them. That is, some of these tools identify points that only exist under certain assumptions. For example, the reference “Extension”, which we saw in a previous video, shows, precisely, a vector that indicates the meaning that a line or an arc would have 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 on video.
Another example is the reference “Medium between 2 points”, which, as the name implies, serves to establish the midpoint between any two points, even if that point does not belong to any object.

A third case that works in the same direction, that is, to establish points that derive from the geometry of objects but that do not belong to them precisely, is the reference “From”, which allows defining a point at a certain distance from 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 we have illustrated before. 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 “Reference to objects” with the corresponding eyebrow of the “Drawing parameters” dialog.

If in this dialog we activate, for example, the references "Endpoint" and "Center", then those will be the references that we will see automatically when we start a drawing or editing command. If at that time we want to use another reference, we can still use the button on the status bar or the context menu. The difference is that the context menu will only activate the desired object reference temporarily, while the dialog box or the status bar button will leave them active for the following drawing commands. However, it is not convenient 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 large that the effectiveness of the references can be lost. Although it should also be noted that when there are many points of references to active objects, we can place the cursor on a point on the screen and then press the "TAB" key. This will force Autocad to go showing the references near the cursor at that time. 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 these cases, we can use the "None" option in the context menu that appears with the "Shift" key and the right mouse button.

On the other hand, it is evident that Autocad points to an end point, for example, in a different way from what a midpoint points out and this in turn clearly distinguishes itself 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 AutoSnap configuration, which is nothing more than the visual help of the “Object reference”. To configure AutoSnap, we use the “Drawing” tab of the “Options” dialog box that appears with the Autocad start menu.

9.1 .X and .Y Dot Filters

References to objects such as “From”, “Midpoint between 2 points” and “Extension” allow us to understand how Autocad can indicate points that do not exactly match the geometry of existing objects but can be derived from it, an idea that programmers have used to design another drawing tool called "Point filters" that we can illustrate right away.
Suppose we have a line and two circles on the screen and we want to draw a rectangle whose first vertex coincides on the Y axis with the center of the largest circle and on the X axis with the left endpoint of the line. That implies that the first point of the rectangle could have as a reference points of both objects, but not touch any.
To take advantage of references to objects as an allusion to values ​​for the independent X and Y axis, we use the “Point filters”. With these filters, a geometric attribute of an object - the center of a circle, for example - can be used to determine the value of X or Y from another point.
Let's go back to the rectangle, the line and the circles on the screen. We said that the first corner of the rectangle that the command window asks us for coincides in its X coordinate with the left end of the line, so in the command window we will then write “.X” to indicate that we will use a reference to objects but only to indicate the value of that coordinate. As already stated, the value of the Y coordinate coincides with the center of the major circle. To use this point filter in combination with the reference to the object, press “.Y” in the command window. The opposite corner of the rectangle coincides on its X axis with the other end of the line, but on its Y axis with the center of the smaller circle, so we will use the same point filter procedure.

In many cases, we may only use a point filter and an object reference only for the X coordinate, and for the Y coordinate we give an absolute value, or an absolute value in X and a Y-reference filter. In any case, combined use Filters and object references allows us to take advantage of the location of existing objects even if they do not intersect or fully match their points with other objects.