MGED provides several different ways to modify and reposition BRL-CAD Primitives by changing the values of their associated parameters:

• the primitive object editor dialog box
• the interactive editing commands
• the get and put TCL commands

See also: Determining the properties of primitive objects

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Primitive Editor

Most of the parameters associated with many primitive objects can be edited using the Primitive Editor dialog box:

1. Invoke the GUI Edit-->Primitive Editor command to display that dialog.
2. Type the object's name into the Name: field and then click the Reset button to display its associated form and the current values of its editable parameters.
3. Interactively change and reposition the object by changing appropriate parameter values. Your changes are immediately written to the database and the object is redrawn in the Display Window each time you click the Apply or OK button (OK also closes the dialog box). Unapplied changes can be undone by clicking the Reset button.
4. Repeat the above steps to edit additional objects, or click the OK or Dismiss button to close the dialog.

Note that forms have not been defined for all object types. Those that lack such forms cannot be edited using this method.

Interactive editing

Any currently displayed primitive object can be selected for modification or relocation using either the GUI Edit-->Primitive Selection... or the CLI [sed] (MGED_CMD_sed.md) command.

Objects that aren't currently displayed will not be listed in the Primitive Selection Menu dialog, and the sed command will display an error message if you try to edit such an object. In either case, using the CLI draw or B command to display such an object would then allow you to select it for editing.

When such an object is selected for editing, the Edit menu will display a set of commands specific to the corresponding primitive type. Invoking any such command will allow you to change the corresponding parameter(s) by entering CLI p commands or activating the Graphics Window and using associated shift grip mouse actions. Similarly, the CLI will enable various edit-mode commands that can be used to modify or relocate the selected primitive. As you use either approach to make such changes, you can:

• record the changes you have made so far by invoking the GUI Edit-->Apply or entering the CLI apply command;
• undo any unrecorded changes by invoking the GUI Edit-->Reset or entering the CLI reset command;
• record the changes you have made and return to viewing mode by invoking the GUI Edit-->Accept or entering the CLI accept command; or
• discard any unrecorded changes and return to the viewing mode by invoking the GUI Edit-->Reject or entering the CLI reject command. You can also reject unrecorded changes by pressing the escape key while the Graphics Window is active.

TCL Commands

Although it is a cumbersome approach that is best reserved for scripted editing, primitive objects can also be edited by entering TCL get and put commands via the CLI:

1. Enter a "get object_name" command to display the current database entry for that object.
2. Enter a "kill object_name" command to delete that database entry and erase the object from the Graphics Window.
3. Enter a "put object_name properties" command to recreate that object with modified parameter values.
4. Enter a "draw object_name" command to redisplay the object and verify your changes.