2012

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.
If you turn on demand loading with the Enable with Copy option, the program
makes a temporary copy of the referenced drawing and demand loads the
temporary file. You can then demand load the xref while allowing the original
reference drawing to be available for modification. When you turn off demand
loading, the program reads in the entire reference drawing regardless of layer
visibility or clip instances.
Layer and spatial indexes were added in AutoCAD Release 14 and AutoCAD
LT 97. If you externally reference a drawing saved in a release previous to this,
you do not see the same performance benefit as drawings saved with the
indexes. For maximum performance, use demand loading with referenced
drawings saved with layer and spatial indexes turned on in AutoCAD Release
14, AutoCAD LT 97, or more recent versions.
To turn on demand loading
1 Click Tools menu ➤ Options.
2 In the Options dialog box, Open and Save tab, under External References,
select Disabled, Enabled, or Enabled with Copy.
Work with Demand Loading in Large Drawings | 1321