optimze unity project for xr_rm

unity/XR_RM_PICO_UDP_Sender/README.md

@@ -8,11 +8,14 @@ Configured target:
 ```text
 Host = 192.168.9.99
 Port = 15000
-Send Hz = 60
+Send Hz = 90
 Convert Unity To Project Coordinates = true
 Package Name = com.local.xr_rm_udp_sender
 ```
 
+The default send rate is 90 Hz. If the network or headset performance is not
+stable enough on site, lower it manually in the PICO panel to 60 Hz.
+
 Open this folder with the Ubuntu editor installed at:
 
 ```text
@@ -44,6 +47,14 @@ Runtime scene components:
   disables PICO auto sleep, applies Android `KEEP_SCREEN_ON`, and restores
   captured screen/sleep timeouts when sending stops.
 
+Coordinate modes:
+
+- `Project (+Z back)`: ROS-facing output. For `pose_source=pxr_predict`, the
+  measured PICO native pose is converted with `project.x=native.z`,
+  `project.y=native.y`, and `project.z=-native.x`.
+- `Source raw`: sends the source pose without this conversion for field
+  diagnostics only.
+
 The setup menu chooses the UDP target host from `XR_RM_UDP_TARGET_HOST` when
 set. Otherwise it auto-detects a local IPv4 address; on this Ubuntu machine the
 current Wi-Fi address is `192.168.9.99`.