imu sensor description

[guihomework]

Dear Shadow,
in this commit df674fe an imu description was added to the URDF, following the sensor description of URDF, probably this one https://wiki.ros.org/urdf/XML/sensor which is no really "supported". Do you use your own parser ?

however, sensor parsing in URDF is broken for ages now, and we maintain a PR that fixes it (but it still did not get merged) following some newer way (more advanced, to support more types of sensors). see ros/urdf#5 and ros/urdfdom#84
that follows this sensor description proposal https://wiki.ros.org/urdf/XML/sensor/proposals in which "type" is a required field .

At our side your addition now obviously fails to parse, because the type is missing.

[ERROR] No child element defining the sensor.

Would it be harmful to add this field (I can provide a PR) so that your description becomes compatible with this new URDF parser we suggest (hence supporting us in that quest). It will help describe the sensor better.

[beatrizleon]

Hi @guihomework , yes please send us the pr

[guihomework]

Hi,
well, it seems one needs not a tag but a child element. An ideal child element could be <imu /> but the current xacro (melodic) complains that the imu element is interpreted for now as a call to the xacro:imu macro...
There are two ways to solve our problem in the sensor parser:

1. add a child element called <unknown_type /> for the moment, but this is not helpful as it does not add any value to the description of the sensor in urdf
2. rename the xacro macro imu to imu_sensor for instance, and then use the child element.

Overall, how is this sensor description used ? is it detected my name in your own parser somewhere ? There is already a link imu and an associated joint which probably is what you need to get TF transforms from palm to IMU, so what is the sensor tag useful for ?
I don't want to make you solve our problems if this is not going to be useful in the future somehow

[guihomework]

#72 is the solution 2)