How to add texture to ground plane in Gazebo?

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Hi all,

I'm using gazebo9 in ROS melodic and I'm following this answer to change the default material of the ground_plane model with a chess board.

Unfortunately, this is the result I get.

I triple checked the model, material and config files and everything is like explained in the post. Does anyone know what I'm doing wrong?

Additionally. I'd like to store this modified model in a ROS package. How can I do that?

Thanks.