It's a feature actually, though I agree it's not a good idea to change the units by default. The wanted behavior is different depending if you are importing an entire scene, or adding an object into an existing scene.

hmm, maybe i didn't explained it good enough, sorry. I join the example file. It's a 2m cube, import it in the default scene after setting meter, with default blender's cube, 2m then too) and compare the 2 cubes. Everything that was in Blender before the import get weird measures.

I understand what you're saying, but this option was implemented with the idea that you'd be importing an entire collada scene, with unit settings included. Which in your case clearly is not useful behavior.

I could add the checkmark as also proposed in the other reportto the importer "import metric" which could be disabled by default (or enabled whatever is more convenient).

Yes, would be nice to add a checkmark. At least, if continuing with inches, that a 2m cube made in Blender and a 2m imported cube get the same size.

I'm not an expert with float precision, but importing a scene and then using 0,0254 as scale for world may reduce precision ? I import scenes that are sometime 2km big, they are 2km big in blender after 0,0254 scale, that means they are about 78 km big (x and y) at scale 1. Maybe doing the conversion to BU/meter during import would increase accuracy, i noticed some weird distortions at edges of such big planes.

Adding an option seems a good solution yes. Probably should be called "Import Units" since it's not only metric units that are supported. Actually scaling objects to match units could be done too, but would not consider that needed as a bugfix, the Collada importer can be improved in many ways.

The problem is more visible in SketchUp because it always export the models as Imperial, even if you were working with meters.

I think the whole point here is not to "keep the scene in meters". One can easily go to scene panel and switch back to meters, and the 2*2*2 cube will be 2*2*2 meters.
The actual problem is the scale factor, because if one was working in the scene before and want to add an asset from a .dae file, the (x) meter = 1blender unit has to be the same for the imported models. So basically I wouldn't ever change the scene "scale", but the other way around. And I do think it's a bug, if it's an option I hope it can be True by default.

Your reported issue has been fixed in SVN. Thanks for taking the
time to report!.

partial fix in revision 54411
Note: When the import Units option is disabled, then we might need to adjust the imported object scalings to match Blender's current settings. This is not yet implemented and will be done after 2.66. Please feel free to add a feature request to the Collada Wiki Page at:

http://wiki.blender.org/index.php/Dev:2.5/Source/Development/Todo/Import_Export

Closing.

In svn revision 54442 i have added scale adjustment during import.

By default Blender now tries to match the scales such that units are preserved. Thus for example:

- in Blender scene set to metric, factor 0.01 -> 1 BL_UNIT equals 1 cm
- In Collada file: unit = 1 Meter
- assume a cylinder of length 1 meter in Collada file

After import the cylinder will have 100 Blender units and it will still be of size 1 meter.
I have briefly tested with Imperial units. Unit type NONE is mapped to 1 BL_UNIT==1 Meter

Please can you test that in depth ? I think i made it correct, but it really can be helpful to have a second opinion on that :)