Some questions about <uri> in sdf files

asked 2023-06-14 08:40:12 -0500

biagio
3 ●1 ●1 ●3

updated 2023-06-14 10:53:54 -0500

Hi to all.

I was reading the Gazebo documentation and I have some questions to which I was not able to find an answer neither in the documentation nor on the forums.

As far I as I have understood, Gazebo has a bunch of environmental variable that expand to a list of path in the system to look for files. Copy pasting from my notes we have:

GAZEBO_MODEL_PATH: colon-separated set of directories where Gazebo will search for models
GAZEBO_RESOURCE_PATH: colon separated set of directories where Gazebo will search for other resources such as world and media files
GAZEBO_MASTER_URI: uri of the gazebo master. This specifies the IP and port where the server will be started and tells the clients where to connect to.
GAZEBO_PLUGIN_PATH: colon-separated set of directories where Gazebo will search for the plugin shared libraries at runtime
GAZEBO_MODEL_DATABASE_PATH: URI of the online model database where Gazebo will download model from

Now, when we build a model using an sdf file, we can use the tag <uri>path_to_resource</uri> to look for specific resources, such as meshes, models and so on. In the documentation and online tutorial, I have often found things like

<uri>model://path</uri>

<uri>file://path</uri>

Now, I guess that model:// is just a place holder for GAZEBO_MODEL_PATH.

My questions are:

what does file:// correspond to?
Are there any other place holder I have not yet seen?
Can you point me to a place in the documentation where this place holders are defined?

Thanks for your time and patience.

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2 Answers

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answered 2023-06-15 06:44:57 -0500

jrtg
31 ●5 ●6 ●9

updated 2023-06-21 07:52:15 -0500

I had a further look:

Wrt. model://:

Based on this documentation, I conclude that model:// is replaced by:

GZ_SIM_RESOURCE_PATH for Gazebo Sim, and
GAZEBO_MODEL_PATH and/or GAZEBO_RESOURCE_PATH for Gazebo Classic

I cannot find the latter two in the Gazebo Sim source code, so these seem for Gazebo Classic only.

Wrt. file://:

Based on this comment in the code (for Gazebo Sim, not sure about Classic), I conclude that file:// can be followed by either a relative path or an absolute path.

Lines 43-47 of the comment contradict with line 53 but I can confirm that -for my use case- file://rel/path seems to work just fine for a relative path.

Wrt. other environment variables:

A grep through the source code of Gazebo Sim yields following list. The IGN ones are deprecated in Garden

GZ_FILE_PATH
GZ_GUI_PLUGIN_PATH
GZ_GUI_RESOURCE_PATH
GZ_LAUNCH_CONFIG_PATH
GZ_LAUNCH_PLUGIN_PATH
GZ_PLUGIN_PATH
GZ_RENDERING_PLUGIN_PATH
GZ_SIM_PHYSICS_ENGINE_PATH
GZ_SIM_RENDER_ENGINE_PATH
GZ_SIM_RESOURCE_PATH
GZ_SIM_SERVER_CONFIG_PATH
GZ_SIM_SYSTEM_PLUGIN_PATH
IGN_FILE_PATH
IGN_GAZEBO_RESOURCE_PATH
IGN_GAZEBO_SYSTEM_PLUGIN_PATH
IGN_GUI_PLUGIN_PATH
IGN_LAUNCH_CONFIG_PATH
IGN_LAUNCH_PLUGIN_PATH
IGN_PLUGIN_PATH
IGN_RENDERING_PLUGIN_PATH
SDF_PATH

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Thank you very much for the help! I also had a look in these days at the other discussion you linked https://osrf-migration.github.io/sdfo...

As far as I understood, in Gazebo Classic it worked like this:

models:// was replaced byGAZEBO_MODEL_PATH
file:// was replaced by GAZEBO_RESOURCE_PATH
The behavior of Gazebo Sim for file:// was changed to respect some standard about URI files: https://en.wikipedia.org/wiki/File_UR...