Add URDF model and visualization script

- Created software/src/lerobot/robots/alohamini/alohamini.urdf with base, lift, and dual arms
- Created software/examples/debug/visualize_urdf.py to visualize URDF in Rerun

Author: blankey1337

software/examples/debug/visualize_urdf.py

@@ -0,0 +1,186 @@
+import argparse
+import time
+import math
+import xml.etree.ElementTree as ET
+import numpy as np
+import rerun as rr
+from scipy.spatial.transform import Rotation as R
+
+def parse_urdf(urdf_path):
+    tree = ET.parse(urdf_path)
+    root = tree.getroot()
+    
+    links = {}
+    joints = []
+
+    for link in root.findall('link'):
+        name = link.get('name')
+        visual = link.find('visual')
+        geometry_info = None
+        color_info = None
+        origin_info = None
+        
+        if visual is not None:
+            geo = visual.find('geometry')
+            if geo is not None:
+                box = geo.find('box')
+                cylinder = geo.find('cylinder')
+                if box is not None:
+                    geometry_info = {'type': 'box', 'size': [float(x) for x in box.get('size').split()]}
+                elif cylinder is not None:
+                    geometry_info = {'type': 'cylinder', 'length': float(cylinder.get('length')), 'radius': float(cylinder.get('radius'))}
+            
+            mat = visual.find('material')
+            if mat is not None:
+                color_info = mat.get('name') # Simplified
+            
+            orig = visual.find('origin')
+            if orig is not None:
+                xyz = [float(x) for x in orig.get('xyz', '0 0 0').split()]
+                rpy = [float(x) for x in orig.get('rpy', '0 0 0').split()]
+                origin_info = {'xyz': xyz, 'rpy': rpy}
+            else:
+                origin_info = {'xyz': [0,0,0], 'rpy': [0,0,0]}
+
+        links[name] = {
+            'visual': geometry_info,
+            'color': color_info,
+            'visual_origin': origin_info
+        }
+
+    for joint in root.findall('joint'):
+        name = joint.get('name')
+        type_ = joint.get('type')
+        parent = joint.find('parent').get('link')
+        child = joint.find('child').get('link')
+        
+        origin = joint.find('origin')
+        xyz = [float(x) for x in origin.get('xyz', '0 0 0').split()] if origin is not None else [0,0,0]
+        rpy = [float(x) for x in origin.get('rpy', '0 0 0').split()] if origin is not None else [0,0,0]
+        
+        axis_elem = joint.find('axis')
+        axis = [float(x) for x in axis_elem.get('xyz', '1 0 0').split()] if axis_elem is not None else [1,0,0]
+
+        limit = joint.find('limit')
+        limits = None
+        if limit is not None:
+            limits = (float(limit.get('lower', -3.14)), float(limit.get('upper', 3.14)))
+
+        joints.append({
+            'name': name,
+            'type': type_,
+            'parent': parent,
+            'child': child,
+            'xyz': xyz,
+            'rpy': rpy,
+            'axis': axis,
+            'limits': limits
+        })
+
+    return links, joints
+
+def get_transform(xyz, rpy):
+    rot = R.from_euler('xyz', rpy).as_matrix()
+    T = np.eye(4)
+    T[:3, :3] = rot
+    T[:3, 3] = xyz
+    return T
+
+def visualize(urdf_path):
+    rr.init("urdf_visualizer", spawn=True)
+    
+    links, joints = parse_urdf(urdf_path)
+    
+    # Build tree structure
+    # joint_map: parent_link -> list of joints where this link is parent
+    joint_map = {}
+    for j in joints:
+        p = j['parent']
+        if p not in joint_map:
+            joint_map[p] = []
+        joint_map[p].append(j)
+
+    # State
+    t = 0.0
+    
+    while True:
+        # Update joint values (sine waves)
+        joint_values = {}
+        for j in joints:
+            if j['type'] in ['revolute', 'continuous']:
+                val = math.sin(t + sum(map(ord, j['name']))) # Random phase
+                joint_values[j['name']] = val
+            elif j['type'] == 'prismatic':
+                val = 0.3 + 0.3 * math.sin(t)
+                joint_values[j['name']] = val
+            else:
+                joint_values[j['name']] = 0.0
+
+        # FK
+        # Stack: (link_name, accumulated_transform)
+        stack = [('base_link', np.eye(4))]
+        
+        while stack:
+            link_name, T_parent = stack.pop()
+            
+            # Log link visual
+            link_data = links.get(link_name)
+            if link_data and link_data['visual']:
+                # Visual origin offset
+                v_orig = link_data['visual_origin']
+                T_visual_offset = get_transform(v_orig['xyz'], v_orig['rpy'])
+                T_visual = T_parent @ T_visual_offset
+                
+                rr.set_time_seconds("sim_time", t)
+                
+                # Decompose for rerun
+                trans = T_visual[:3, 3]
+                rot = R.from_matrix(T_visual[:3, :3]).as_quat() # xyzw
+                # Rearrange to xyzw for scipy -> xyzw for rerun (check convention, rerun uses xyzw)
+                
+                entity_path = f"robot/{link_name}"
+                
+                geo = link_data['visual']
+                if geo['type'] == 'box':
+                    rr.log(entity_path, rr.Boxes3D(half_sizes=[s/2 for s in geo['size']], centers=[0,0,0]), rr.Transform3D(translation=trans, rotation=rr.Quaternion(xyzw=rot)))
+                elif geo['type'] == 'cylinder':
+                    # Rerun cylinder is along Z?
+                    # URDF cylinder is along Z (usually)
+                    # We might need to check visualization, but simple logging:
+                    # Rerun doesn't have Cylinder3D primitive in older versions, checking...
+                    # It does have standard primitives now? Or we use Mesh3D / Points.
+                    # As fallback, log a box approximating cylinder or use Points if needed. 
+                    # Use Box for now to be safe and simple.
+                    rr.log(entity_path, rr.Boxes3D(half_sizes=[geo['radius'], geo['radius'], geo['length']/2], centers=[0,0,0]), rr.Transform3D(translation=trans, rotation=rr.Quaternion(xyzw=rot)))
+
+            # Children
+            children_joints = joint_map.get(link_name, [])
+            for j in children_joints:
+                # Static transform
+                T_static = get_transform(j['xyz'], j['rpy'])
+                
+                # Joint transform
+                T_joint = np.eye(4)
+                if j['type'] in ['revolute', 'continuous']:
+                    angle = joint_values.get(j['name'], 0)
+                    axis = np.array(j['axis'])
+                    # Axis-angle rotation
+                    rot_j = R.from_rotvec(axis * angle).as_matrix()
+                    T_joint[:3, :3] = rot_j
+                elif j['type'] == 'prismatic':
+                    dist = joint_values.get(j['name'], 0)
+                    axis = np.array(j['axis'])
+                    T_joint[:3, 3] = axis * dist
+                
+                T_child = T_parent @ T_static @ T_joint
+                stack.append((j['child'], T_child))
+
+        t += 0.05
+        time.sleep(0.05)
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser()
+    parser.add_argument("--urdf", default="../../src/lerobot/robots/alohamini/alohamini.urdf")
+    args = parser.parse_args()
+    
+    visualize(args.urdf)