When importing Collada *.dae model files into Blender 3D and they fail to display in the 3D View (indicative of a successful import), run through the following check-list of items (assumes the imported mesh has no fundamental problems causing a failed export);
- Make sure the correct importer is used. Depending on the version of Blender used it's possible to import two 'versions' of the Collada format, neither of which is backward/forward compatible with the other i.e., importing a *.dae file using the 1.4 import script when the model was exported using 1.3 specifications will fail Collada (note: this applies largely to Blender 2.49 or below as Blender uses the current Collada codebase as the basis for its import/export capabilities).
- Check Layers. Blender can import to the active layer (script dependent) so if the mesh is not on layer being used (any layer other than "1") it may have been placed on another (typically layer "1" if other layers are being used/model is imported to).
- Check Grid settings. Generally speaking Blender use a smaller scale/size system than other 3D applications. This can lead to imported models being so big they appear invisible because they're outside the default camera clipping distance. Increasing camera clip will often display excessively large models (by Blenders standards).
- Check the model. Check the model in an appropriate model viewer or other third party model viewing application capable of displaying *dae files to make sure there are no fundamental issues with the mesh itself - if it fails to appear here it's likely there is a fundamental problem causing import failure into Blender.
If all the above still result in a broken or incomplete import than it's likely the mesh is corrupted in some fashion and will need to be re-exported from the source or possibly converted into another format that's more broadly importable (with the potential loss of any animations, materials and UVW maps).