2012

Table Of Contents
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.
Work with Layer and Spatial Indexes
To receive the maximum benefit of demand loading, it is recommended that
you save any drawings that are used as xrefs with layer and spatial indexes.
A layer index is a list showing which objects are on which layers. This list is
used when the program is referencing the drawing in conjunction with demand
loading to determine which objects need to be read in and displayed. Objects
on frozen layers in a referenced drawing are not read in if the referenced
drawing has a layer index and is being demand loaded.
The spatial index organizes objects based on their location in 3D space. This
organization is used to efficiently determine which objects need to be read in
when the drawing is being demand loaded and clipped as an xref. If demand
loading is turned on, and the drawing is attached as an xref and clipped, the
program uses the spatial index in the externally referenced drawing to
determine which objects lie within the clip boundary. The program then reads
only those objects into the current session.
Spatial and layer indexes are best used in drawings that will be used as xrefs
in other drawings where demand loading is enabled. Drawings that are not
going to be used as xrefs or partially opened will not benefit from layer and
spatial indexing or demand loading.
Set Paths for Temporary Xref File Copies
When you turn on demand loading with copy, you can control where copies
of externally referenced drawings are to be placed.
When you turn on demand loading with copy, the XLOADPATH system
variable can be used to indicate the path where copies of externally referenced
drawings are to be placed. The path you specify remains in effect for all drawing
sessions until you indicate a different path. If no value for XLOADPATH is
specified, the temporary file copies are placed in the standard folder for
temporary files.
If you find that referencing drawings over a network is slow, it is recommended
that you set XLOADPATH to reference a local folder, and set XLOADCTL to
2 so that the externally referenced files are demand loaded from your local
740 | Chapter 11 Share Data Between Files