unable to parse urdf file

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Hello everyone,

The question is extremely simple: when I type the line (quoted):

<origin xyz="${reflect*camera_offset_x} 0 0" rpy="0 ${camera_offset_p} 0" />

the urdf is parsed, everything is great, I can visualize in rviz and when I type:

<origin xyz="${reflect*camera_offset_x} 0 0" rpy="0 ${reflect*camera_offset_p} 0" />

it doesn't work anymore..

Here, reflect can be 1 or -1 and it seems to by no problem for entering negative values for the angle offsets...

So where the hell could the problem come from?

Thanks for your time. Yours, Lucian