Other Hatching Considerations
There are several other considerations to keep in mind when creating and working with hatch objects. These include the hiding, or turning hatching off; exploding hatch objects into their constituent lines; and controlling whether associative hatch objects include their boundaries when selected for an editing operation.
Aligning Hatch Objects
Areas hatched with the same pattern and with the same scale and angle parameters will have the corresponding elements in the pattern lined up in adjacent areas. All hatch patterns are referenced to the snap origin, which usually coincides with the drawing’s 0,0. If you want to realign a hatch pattern, change the snap origin before drawing the hatch. The snap origin is controlled by the system variable, SNAPBASE, which stores the value of a point. Set SNAPBASE to a point other than 0,0 by picking a point such as the corner of a rectangular area, to cause the next hatch object drawn to align with the current snap origin.
The reason for this stems from the fact that families of lines in the pattern were defined with the same base point and angle and this is true no matter where the patterns appear in the drawing. This causes hatching lines to line up in adjacent areas. All hatch patterns are referenced to the snap origin, which by default is the drawing’s 0,0 origin.
Exploding Hatch Objects
You can explode a hatch object into its constituent lines with the EXPLODE command. Exploding a hatch object removes any associativity. Additionally, the grouped set of line objects that make up the pattern replaces the single hatch object. Although exploding a hatch object does enable you to edit the individual lines of the hatch, in most cases you lose more productivity than you gain.
Note
Because a hatch object is composed of lines, you can use the same object snap modes (such as endpoint and midpoint) on the individual lines in hatch objects, associative or exploded, as you use on line objects.
Controlling Visibility with FILLMODE
You can control the visibility of all hatch objects in a drawing by setting the FILLMODE system variable to 0. With FILLMODE off (set to 0), all hatch objects become invisible regardless of the status of the layers on which the hatch objects reside. You must issue the REGEN or REGENALL command after changing FILLMODE for the change in visibility to take effect.
The disadvantage of using FILLMODE to control hatch object visibility is that FILLMODE also controls the fill of other objects such as wide polylines and multilines. If you want to hide hatching more selectively, place hatching objects on separate layers so that the layers can be turned on and off without affecting other elements of the drawing.
Selecting Hatch Objects and Their Boundaries
Usually, you will want to select both an associative hatch and its boundary for editing operations such as moving, mirroring, or copying. By default, however, AutoCAD treats the two elements separately during the object selection process. To speed hatch and boundary selection, you can change the PICKSTYLE system variable from its default value of 1 to a value of 3. The PICKSTYLE system variable controls the selection of groups and hatch elements. A setting of 0 or 1 disables simultaneous hatch and boundary element selection. A value of 2 or 3 enables simultaneous hatch and boundary selection.
Using Point Acquisition with the HATCH Command
The older version of the BHATCH command is HATCH. Although BHATCH replaced HATCH in functionality and especially the ability to calculate boundaries, HATCH is still supported. The principle disadvantage of the HATCH command is that it can create only non-associative hatch objects.
Despite its drawbacks, HATCH does have an option that you may find useful: the Direct Hatch option. The Direct Hatch option enables you to define an area to be hatched on-the-fly, negating the necessity to draw boundary objects before drawing the hatch object. The Direct Hatch option, or point acquisition method, is useful when you want to “suggest” large hatch areas by hatching only a few representative patches. This method is shown in the following exercise.
Exercise 16.5 Understanding Hatch Associativity
1. |
Return to Chap16.dwg. Start the HATCH command by typing HATCH
at the Command: prompt. Press Enter to accept the default ANSI31 hatch pattern. |
2. |
At the next two command-line prompts, type 0.75
for the pattern scale and then press Enter to accept the default of 0 for the pattern angle. |
3. |
At the Select objects: prompt, press Enter to indicate that you will be specifying points instead of objects. |
4. |
Type N
to indicate that you want to discard the polyline boundary after the hatch is completed. |
5. |
Referring to the left portion of Figure 16.19, use an Endpoint osnap to pick 1 and then pick points 2 through 9. Use an Endpoint osnap to pick point 10, then type C
, and press Enter to create and close the polyline boundary on-the-fly. |
6. | |
7. |
Save your work and close the drawing. |
