Visuals and collision transforms match the wrong link

[Hugo-Suricate]

Description

World transforms of the visuals and collisions attached to a chain are incorrectly computed. Their transform is computed relative to the parent link instead of the current one.

Example using a simple URDF and k::Chain::from_urdf_file() shows each link's visual geometry has the wrong parent transform. Visuals are systematically offset by one link in the hierarchy.

Environment

k crate version: 0.32.0
Platform: [Win 10]
Rust version: [1.97.1]

Minimal Reproduction Files:

minimal_test.urdf

<?xml version="1.0"?>
<robot name="test_robot">
  <link name="base_link">
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
        <box size="0.1 0.1 0.1"/>
      </geometry>
    </visual>
  </link>

  <!-- First Joint: base_link -> link_1 with Z offset -->
  <joint name="joint_0" type="revolute">
    <parent link="base_link"/>
    <child link="link_1"/>
    <origin xyz="0 0 0.2" rpy="0 0 0"/>
    <axis xyz="0 0 1"/>
    <limit lower="-3.14" upper="3.14" effort="100" velocity="1.0"/>
  </joint>
  
  <link name="link_1">
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
        <cylinder radius="0.05" length="0.1"/>
      </geometry>
    </visual>
  </link>
  
  <!-- Second Joint: link_1 -> link_2 with Z offset -->
  <joint name="joint_1" type="revolute">
    <parent link="link_1"/>
    <child link="link_2"/>
    <origin xyz="0 0 0.3" rpy="0 0 0"/>
    <axis xyz="0 0 1"/>
    <limit lower="-3.14" upper="3.14" effort="100" velocity="1.0"/>
  </joint>
  
  <link name="link_2">
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
        <sphere radius="0.05"/>
      </geometry>
    </visual>
  </link>
  
</robot>

src/main.rs

use k::{Chain};

fn main() {
    let chain = Chain::<f32>::from_urdf_file("minimal_test.urdf").unwrap();
    chain.update_link_transforms();
    
    println!("{}\n", chain);
    
    // Local translations
    println!("Joints: ");
    for joint in chain.iter_joints() {
        println!("{} joint local translation : {:?}", joint.name, joint.local_transform().translation);
        println!("{} joint world translation : {:?}", joint.name, joint.world_transform().unwrap().translation);
    }

    println!("\nLink visuals: ");
    for link in chain.iter_links() {
        println!("{} visual world translation : {:?}", &link.name, &link.visuals.first().unwrap().world_transform().unwrap().translation);
    }
}

link_1 visual should match link_1 world position (i.e. joint_0) but doesn't : matches base_link instead
link_2 visual should match link_2 world position (i.e. joint_1) but doesn't : matches joint_0 instead

Probable root cause and fix

In src/chain.rs in the update_link_transforms(), line 491, the transform is computed with parent_world_transform(). Replace with world_transform() and rename the variable to avoid confusion.