When to use the Layer & Spatial Index

June 9, 2010 at 9:04 pm 2 comments

I was triggered to write this blog when I read an article about External References also known as XREFs, tweeted by Edwin Prakoso. I was doing the preparation of an AutoCAD course a while ago when I was looking for some answers to cover this topic. 
There are good articles to find on the internet how to use eXternal References in AutoCAD products. But what I’m interested in is, how the Layer & Spatial Index will work for you or benefit you when using with Xrefs.
To understand this topic you first need to understand how Xrefs works. Herefor I refer to an article from CAD-Notes: Using XREF, Attachment or Overlay.

What is the Layer & Spatial Index?
An index is a typical term used with databases for finding records as fast as possible. You could see an index like a rolodex which you use for fast and easy access of the addresses and telephone numbers of all your contacts. The index used this way is typically alfabetically ordered from A to Z.

Using an index will keep track of the objects so they can be found fast in a drawing.
There are two types of indices:

  1. Layer Index, is used to gain optimized access of objects on a layer.
    Actually it is a list showing which objects are on which layer.
  2. Spatial Index is used to gain optimized access of the geometric location of objects in space.

Using an index will make the drawing slightly bigger in file size. This has to do with storing the index information with the drawing.

When to use
There are two ways when you can use the Layer & Spatial Index.

  1. Xref clipping
  2. Partial Open/Load 

Xref clipping
When used with Xrefs, loading of related drawing information will go faster then without. I’ve used the word ‘related’, because it works great with clipped Xrefs.
But remember: the use of the Layer & Spatial Index for Xrefs only works best when Demand Loading for Xrefs is turned on. Demand loading is a feature to load only xref data that’s necessary to regenerate the drawing. It works great with large drawings or many objects on frozen layers in Xrefs.
You can find these settings in the Options, the Open and Save tab, under External References (Xrefs).

Or you can also use and set the AutoCAD drawing variable XLOADCTL to 2.
With this value set, demand loading is turned on and a copy of the Xref will be used for attaching the drawing leaving the original in place for editing purposes by another session.

Partial Open/Load
Another method of using the Layer & Spatial Index is when opening, mostly large or big, drawings. And you want only a portion or part of that drawing being loaded for editing purposes. This will result in faster loading of the drawing with the pre-selected objects.
For partial opening a drawing you do the following: when opening a drawing, you can click on the down arrow on the right of the Open button and click Partial Open:

You can partially open drawings by loading objects within a Window (which will benefit when using the Spatial Index) and/or loading objects from selected layers (which will benefit when using the Layer Index). 

Later you can partially load additional data to this partial opened drawing by using the PARTIALOAD command.  This will open a window like above where you can select additional layers from where to load the objects.

Activating the Layer & Spatial Indices
You can use the Layer & Spatial Index by saving it with your drawing. You can do this two ways:

  1. by going to the Saveas command, Tools (upper right corner) and click on Options.This opens a window where you can activate the Layer and/or Spatial Index.
  2. or you can also use and set the AutoCAD drawing variable INDEXCTL to 3.

So why not always use this index turned on with all drawings?
Well not every user works with large drawings or uses Xrefs. Not using the Layer & Spatial Index will save you disk storage space.

If you have any questions or comment on this topic, please do so to make this topic valuable for everyone.

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Entry filed under: AutoCAD Civil 3D, AutoCAD General, External References.

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