2011

Table Of Contents
Quick Reference
Commands
EXTERNALREFERENCES
Opens the External References palette.
System Variables
XLOADCTL
Turns xref demand-loading on and off, and controls whether it opens the
referenced drawing or a copy.
Work with Demand Loading
With demand loading, only the data from the referenced drawing that is
necessary to regenerate the current drawing is loaded into memory.
To realize the maximum benefits of demand loading, you need to save the
referenced drawings with layer and spatial indexes. The performance benefits
of demand loading are most noticeable when you do one of the following:
Clip the xref with the program to display a small fraction of it. A spatial
index is saved in the externally referenced drawing.
Freeze several layers of the xref. The externally referenced drawing is saved
with a layer index.
If demand loading is turned on, and you have clipped xrefs that were saved
with spatial indexes, objects in the referenced drawing database that are
contained within the clip volume comprise the majority of the objects read
into the drawing. If the clip volume is modified, more objects are loaded as
required from the reference drawing. Similarly, if you have xrefs with many
layers frozen that were saved with layer indexes, only the objects on those
thawed layers are read into the current drawing. If those xref-dependent layers
are thawed, the program reads in that geometry from the reference drawing
as required.
When demand loading is turned on, the program places a lock on all reference
drawings so that it can read in any geometry it needs to on demand. Other
users can open those reference drawings, but they cannot save changes to
them. If you want other users to be able to modify an xref that is being demand
loaded into another drawing, use demand loading with the Copy option.
1214 | Chapter 31 Reference Other Drawing Files