Skeletons

How to add skeletons to a neurglancer precomputed layer:

Modify the info file adding 'skeletons': 'path/to/skeletons/folder'

Add skeletons using the skeleton.py encoder.

Binary format:
* 4 bytes little-endian unsigned int number of vertex
* 4 bytes little-endian unsigned int number of edges
* number of vertex * 3 float32 
* vertex attributes (info file doesn't yet support specifying them)
* number of edges  * 2 uint32

the filename is simply the segment ID. one file per object, no manifest file. the coordinate for mesh and skeleton should be physical dimension, not voxel-based.

Now when you click on a segment the skeleton will be displayed if available.