Using URIs in COLLADA

COLLADA uses URIs exclusively to reference resources or files. The URIs must be of the correct standard format to work correctly. A common mistake is to use Windows or Linux paths as URIs. This article describes the correct standardized URI and gives examples.

URI syntax

A file path needs to be converted to a file scheme URI before being passed to the COLLADA DOM. ((EDITOR: This page needs the following improvement: This also applies to COLLADA, not just the DOM, right? ))

The basic URI syntax is:

scheme://authority/filepath?query#fragment

URIs are either absolute or relative:

• An absolute URI contains a scheme and an authority.
• A relative URI is any URI that does not contain a scheme and authority. A relative URI can be a relative path, an absolute path, or just a fragment.

The fragment portion identifies elements by using their id attribute. This attribute references an element that can be found within the same document as the URI. An example of this:

#redMaterial

For example:

file:///c:/path/document.dae#Geo_01

is an absolute URI that references a file named document.dae on the localhost found in c:/path; it references an element with an id of "Geo_01".

Examples of relative path URIs:

./path/document.dae
../../../path/document.dae#elementID
document.dae#Geo_01

Normalizing relative URIs

A base URI is needed to normalize relative URIs. Absolute URIs do not require a separate base URI.

Assuming a base URI of

file:///c:/A/B/C/D/doc.dae

here are some examples of how the following URIs are normalized:

Original URI	Normalized URI
./path/document.dae	file:///c:/A/B/C/D/path/document.dae
../../../path/document.dae#elementID	file:///A/path/document.dae#elementID
/c:/path/document.dae#Light01	file:///c:/path/document.dae#Light01
c:/path/document.dae	file:///c:/A/B/C/D/c:/path/document.dae

Windows paths and URIs

A Windows absolute path must be preceded by a forward slash character '/'. An example:

/c:/path/document.dae#Light01

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.

The following are some examples of converting a file path to a URI.

Example Description	File Path	URI
Windows absolute path	C:\folder\file.dae	file:///C:/folder/file.dae
Windows relative path	..\folder\file.dae	../folder/file.dae
UNC path	\\remoteMachine\folder\file.dae	file://///remoteMachine/folder/file.dae
Linux absolute path	/folder/file.dae	file:///folder/file.dae
Linux relative path	../folder/file.dae	../folder/file.dae

See also

• DOM resolver subsystem
• DOM URI resolver system
• DOM guide: Resolving URIs