Issues Building PX4 Package on ROS melodic/Ubuntu 18

[Naza]

I understand that PX4 is recommending ROS melodic with Ubuntu 18, so I reinstalled these versions and tried to build PX4 following the instructions in: Building the Code · PX4 Developer Guide

I can run the jMAVSim using the following command:

make px4_sitl jmavsim

But when I try to build catkin, in order to use GAZEBO with PX4 launch files, I get the following error:

What is wrong? How can I run PX4 launch files to use IRIS vehicles in GAZEBO and mavros?

Thank you

[Naza]

This is the error I get when I try to launch PX4 files