What is a .dae file?

What COLLADA is

COLLADA (COLLAborative Design Activity) is an XML schema for 3D scenes, originally from Sony and later managed by Khronos. It was the interchange format of the 2000s, and it is still the export path of choice out of several tools, most notably SketchUp and older Blender pipelines.

Being XML, a .dae file is readable and editable. That is its great practical virtue: when a model comes through wrong, you can open the file and see why.

The unit scale, done properly

COLLADA's <asset> block carries a unit:

<unit meter="0.001" name="millimeter"/>
<up_axis>Z_UP</up_axis>

meter is the number of metres in one file unit, so 0.001 means millimetres and 0.0254 means inches. This is a *scale factor*, not a name from a fixed list, so COLLADA can express units that other formats cannot, and occasionally does, when an exporter writes something like meter="0.0254000508".

This site maps the factor back to a named unit where one matches. Where none does, it scales the geometry and says so instead of mislabelling it.

The up-axis, which is the other half of the problem

COLLADA also declares whether the file is Y-up or Z-up. CAD tools are overwhelmingly Z-up; graphics tools are overwhelmingly Y-up. A model that arrives lying on its side almost always crossed that boundary without the declaration being honoured.

This site reads <up_axis> and rotates once on import, so downstream conversions do not each have to guess.

What COLLADA stores

• Geometry as triangles, polylists or polygons, with any number of sides per

face

• Independent indices for position, normal and texture coordinate, which is why

a COLLADA mesh often has more vertices after import than the file's vertex count suggests

• Materials and effects, including colours and textures
• A full node hierarchy with matrices, translations, rotations and scales
• Animation, skinning, physics and kinematics

What it does not

No exact CAD geometry. No parametric history. No manufacturing information.

Why it lost ground

COLLADA is verbose, its schema is permissive enough that two valid files can express the same scene very differently, and exporters disagreed in practice. glTF exists largely because Khronos concluded a leaner, stricter, runtime-oriented format was needed.

For new work, glTF or GLB is the better choice. COLLADA remains the right answer when the tool at one end only speaks it, SketchUp being the common case.

SketchUp, specifically

.dae is the usual way geometry leaves SketchUp for other tools. Watch the export options: SketchUp defaults can produce a Z-up file with unusual units, and you should enable triangulation if the destination is a slicer or a CAD package.