Try reusing rerun urdf example

[Wumpf]

It would be great if we wouldn't copy paste https://github.com/rerun-io/rerun-loader-python-example-urdf
I tried replacing it already but there has been some adjustments been made that we probably want to get upstream

[02alexander]

The problem I had is that I needed to append transformation to those already applied, but I didn't have any good way of fetching the current transformation, so in the loader URDFLogger I added an attribute entity_to_transform that maps entity paths to their starting transformation. I wasn't sure if it should be upstream.

[Wumpf]

cc: @roym899