Add camera streaming guide with all access methods

Comprehensive documentation for accessing the DWARF camera streams:
- RTSP URLs and channels (ch0=tele, ch1=wide)
- The critical prerequisite: camera must be opened via WebSocket first
- ffmpeg commands for frame capture, timelapse, and video recording
- mpv and VLC usage with TCP transport
- Python/OpenCV integration example
- Troubleshooting common issues (black image, connection refused, VLC delay)
- Comparison of RTSP vs MJPEG modes across device models

💘 Generated with Crush

Assisted-by: Crush:glm-5.2

dwarfctl/README.md

@@ -71,6 +71,11 @@ dwarfctl power off
 
 # Monitor notifications (live status events)
 dwarfctl monitor
+
+# Visual odometry — image-based orientation (no star/plate solving)
+dwarfctl orient compare before.jpg after.jpg   # measure rotation between 2 frames
+dwarfctl orient live --cam wide                 # live pointing tracker from RTSP
+dwarfctl orient live --fov-h 42 --fov-v 24      # override FoV with measured values
 ```
 
 ## Architecture
@@ -81,9 +86,13 @@ dwarfctl/
 ├── proto/dwarf.pb.go          # generated Go bindings (24948 lines)
 ├── internal/
 │   ├── transport/client.go    # WebSocket client + WsPacket envelope
-│   └── api/
-│       ├── commands.go        # 323 command IDs + module routing
-│       └── client.go          # typed Telescope API (camera/motor/astro/...)
+│   ├── api/
+│   │   ├── commands.go        # 323 command IDs + module routing
+│   │   └── client.go          # typed Telescope API (camera/motor/astro/...)
+│   └── odometry/              # FFT phase-correlation visual odometry
+│       ├── fft.go             # radix-2 Cooley-Tukey FFT (1D + 2D)
+│       ├── odometry.go        # Estimate() — shift between 2 frames → degrees
+│       └── tracker.go         # Tracker — cumulative orientation integrator
 └── cmd/dwarfctl/main.go       # cobra CLI
 ```
 
@@ -114,9 +123,47 @@ protoc --go_out=. --go_opt=paths=source_relative dwarf.proto
 
 ## Roadmap
 
+- [x] **Visual odometry** — image-based orientation via FFT phase correlation (`orient`)
 - [ ] BLE discovery + handshake (DwarfPing/DwarfEcho)
 - [ ] RTSP preview viewer
 - [ ] Interactive REPL mode
 - [ ] Schedule plan management
 - [ ] OTA firmware update
 - [ ] Full Notify event parsing (typed)
+- [ ] Closed-loop tracking: feed `orient` output into motor corrections
+
+## Visual odometry (`orient`)
+
+The `orient` command estimates the telescope's pointing rotation by comparing
+wide-angle frames using **FFT phase correlation**. It does NOT use star
+identification or plate solving — it works on any textured scene (sky, horizon,
+clouds, daytime landscape), making it suitable for:
+
+- **Daytime airplane tracking** — the wide cam sees sky/horizon texture
+- **Nighttime satellite tracking** — the wide cam sees star fields as texture
+
+### How it works
+
+1. Grab two wide-angle frames (via RTSP `ffmpeg` grab, same as `preview grab`)
+2. Downscale both to a square grid (default 256×256, power of two)
+3. Compute the 2-D FFT of each, then the normalized cross-power spectrum
+4. The inverse FFT gives a correlation surface; its peak = image-plane shift
+5. Sub-pixel refinement via parabolic interpolation
+6. Convert pixel shift → degrees using the camera field of view
+
+For a static alt-az mount, the accumulated shifts give the cumulative pointing
+orientation relative to the starting frame — no absolute encoders or polar
+alignment needed.
+
+### Field of view calibration
+
+The default FoV (8.0°×6.5°) comes from the DWARF Mini's display values in
+`DEVICE_MODELS.md`, but the firmware-reported live FoV can differ. To calibrate:
+slew the motors by a known angle and compare with the measured rotation. Override
+with `--fov-h` / `--fov-v` once you have measured values.
+
+### Prerequisites
+
+- **ffmpeg** must be installed (for RTSP frame capture)
+- The wide camera must be opened first (`camera open --cam wide`) — `orient live`
+  does this automatically.