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URIs are used extensively in COLLADA documents to reference other COLLADA elements or external resources such as texture files, shader source code, and so on. A URI must be formatted properly for the application to find the resource the URI identifies. This article describes how to use URIs in COLLADA.


The COLLADA schema uses the xs:anyURI type to represent URIs. xs:anyURI allows for URI references in addition to URIs, so you can use either a URI or a relative URI reference.

Some examples of URI usage in COLLADA include

  • The target attribute of <instance_material> elements
  • The url attribute on <instance_geometry>, <instance_node>, and <instance_effect> elements
  • The <image>/<init_from> element

For URIs that reference COLLADA elements (like the url attribute on the <instance_geometry> element), the fragment portion identifies the element by its id attribute. An example of this:

<instance_geometry url="file:///models/car.dae#carGeometry />

This <instance_geometry> references the <geometry> element whose ID is carGeometry in the document file:///models/car.dae.

<instance_geometry url="../car.dae#carGeometry />

In this example a relative reference is used. It'll need to be resolved to a URI before the application can obtain the referenced <geometry> element.

Base URIs in a COLLADA document

To resolve relative URI references, a base URI is needed. In COLLADA, the base URI can be specified in the root <COLLADA> element:

<COLLADA xmlns="" version="1.4.1"

If the xml:base attribute isn't specified, then the base URI is the document URI. So if the document URI is "file:///car.dae", then that'll be the base URI used to resolve any relative references in the document.

Paths versus URIs

A file scheme URI is used to represent a file on the local machine. The file scheme is described at File paths need to be converted to file scheme URIs to be used in COLLADA properly. If the base URI's scheme is file (which is usually the case), then you can use a relative reference to the file. When the reference is resolved by the application it'll become a valid file scheme URI.

Below are some examples of specifying a file via a relative URI reference in COLLADA. These examples assume that the base URI's scheme is file, otherwise the reference won't resolve correctly. You might use these examples in the <image>/<init_from> element to refer to an image file on disk.

Example Description File Path URI Reference
Windows absolute path
Windows relative path
UNC path
Linux absolute path
Linux relative path

Note: Windows file paths are not proper URIs. Only the slash (/) character is used as a path delimeter in URIs. Windows uses the backslash (\) to delimit path segments. Using the backslash can result in incorrect URI processing. "A\B\C" is considered one path segment. If using "file:///A\B\C" as a base URI and trying to resolve "../doc.dae" the result will be "file:///doc.dae" and not "file:///A\B\doc.dae" as one might have expected.

See also