With p.DIRECT and useMaximalCoordinates=True, loadURDF will go wrong, while with p.GUI is fine.

[liusida]

I know useMaximalCoordinates is still experimental, but I think it is still worth reporting this bug. It took me a while to figure out it was related to useMaximalCoordinates.

I'll paste the .urdf file and a small piece of Python code for reproducing this bug.

robot.urdf

<?xml version="1.0" ?>
<robot name="sd">
  <material name="base">
    <color rgba="1 0 0 1"/>
  </material>
  <material name="part">
    <color rgba="0 1 0 1"/>
  </material>
  <link name="link_0">
    <inertial>
      <mass value="0.4"/>
      <origin rpy="0 0 0" xyz="0.1 0.1 0.15"/>
      <inertia ixx="0.004" ixy="0.0" ixz="0.0" iyy="0.004" iyz="0.0" izz="0.002"/>
    </inertial>
    <visual>
      <geometry>
        <box size="0.2 0.2 0.3"/>
      </geometry>
      <material name="base"/>
    </visual>
    <collision>
      <geometry>
        <box size="0.2 0.2 0.3"/>
      </geometry>
    </collision>
  </link>
  <link name="link_1">
    <inertial>
      <mass value="0.3"/>
      <origin rpy="0 0 0" xyz="0.1 0.1 0.15"/>
      <inertia ixx="0.003" ixy="0.0" ixz="0.0" iyy="0.003" iyz="0.0" izz="0.002"/>
    </inertial>
    <visual>
      <geometry>
        <box size="0.2 0.2 0.3"/>
      </geometry>
      <material name="part"/>
    </visual>
    <collision>
      <geometry>
        <box size="0.2 0.2 0.3"/>
      </geometry>
    </collision>
  </link>
  <joint name="link_0__link_1" type="revolute">
    <parent link="link_0"/>
    <child link="link_1"/>
    <axis xyz="1 0 0"/>
    <limit effort="3" high="0.02" low="0.01" velocity="3"/>
    <origin xyz=" 0 0 0.36"/>
  </joint>
</robot>

reproduce.py

import pybullet as p
import time

COLOR_YELLOW = "\033[1;33m"
COLOR_OFF = "\033[0m"

def debug(message):
    """Print debug message with color."""
    print(f"{COLOR_YELLOW}{message}{COLOR_OFF}")

debug("First use p.GUI (order doesn't matter).")
p.connect(p.GUI)
robotId = p.loadURDF("robot.urdf", useMaximalCoordinates=True)
n = p.getNumJoints(robotId)
debug(f"urdf_robotId joint number: {n}")
p.disconnect()

debug("Now use p.DIRECT.")
p.connect(p.DIRECT)
robotId = p.loadURDF("robot.urdf", useMaximalCoordinates=True)
n = p.getNumJoints(robotId)
debug(f"urdf_robotId joint number: {n}")
p.disconnect()

debug("If set useMaximalCoordinates to False.")
p.connect(p.DIRECT)
robotId = p.loadURDF("robot.urdf", useMaximalCoordinates=False)
n = p.getNumJoints(robotId)
debug(f"urdf_robotId joint number: {n}")
p.disconnect()

debug("Use p.GUI again.")
p.connect(p.GUI)
robotId = p.loadURDF("robot.urdf", useMaximalCoordinates=True)
n = p.getNumJoints(robotId)
debug(f"urdf_robotId joint number: {n}")
p.disconnect()