The LTMASK command lets you setup the linetype mask for the subsequent object selection via a GUI dialog manner. It will open a dialog window containing 16 check-boxes for the frist 16 linetypes defined in the drawing. You may place a check-mark on a linetype to specify that the objects with the corresponding linetype will be allowed to select during the object selection operation when the selection masking is enabled. See SELECT command for details about the object selection operation.
The linetype mask is controlled by the system variable LTYPEMASK, which is an integer bit-flag variable with volatile attribute and will be reset to 0 each time TwinCAD is initialized. Each bit of the integer from bit 0 to bit 15, corresponds to a linetype ID from 0 to 15. If a bit is set to 1, the entity with the corresponding linetype will be rejected by the object selection operation, provided that the selection mask is enabled. Linetype of [ByLayer] and [ByBlock] are resolved to the actual linetype used for the entity before the masking.
Note that the object with a linetype ID after 15 can not be masked off during the object selection operation.