> ## Documentation Index > Fetch the complete documentation index at: https://docs.altnautica.com/llms.txt > Use this file to discover all available pages before exploring further. # Mode comparison > Side-by-side decision table: pick the right Vision Navigation mode based on hardware, scene, and accuracy needs. # Mode comparison The six estimator modes at a glance. Use this page as a buying decision when you know the hardware you have or the scene you intend to fly. ## Quick decision If you can only read one row of this table, it is this one: | If you have... | Use... | | ------------------------------------------------------ | ----------------------------------------- | | Downward camera + rangefinder | `optical_flow` | | Downward camera only (no rangefinder) | `optical_flow_degraded` | | Forward camera + NPU board | `vio_openvins` | | Forward camera + RK3582 / RK3588S2 board with headroom | `vio_vins_fusion` | | Two cameras + NPU board | `hybrid_of_plus_vio` | | None of the above | `off` (plugin loads, no MAVLink emission) | ## Full comparison | Dimension | `off` | `optical_flow` | `optical_flow_degraded` | `vio_openvins` | `vio_vins_fusion` | `hybrid_of_plus_vio` | | ---------------------------- | --------- | -------------------------------------- | --------------------------------------- | ----------------------------------------------------------------- | ----------------------------------- | ----------------------------------- | | Camera direction | none | downward | downward | forward | forward | downward + forward | | Camera type | none | UVC or CSI | UVC or CSI | global shutter preferred | global shutter preferred | both | | Rangefinder | optional | required | optional | optional | optional | optional | | IMU read | gyro only | gyro only | gyro only | gyro + accel | gyro + accel | gyro + accel | | Output | none | OPTICAL\_FLOW\_RAD | OPTICAL\_FLOW\_RAD | VISION\_POSITION\_ESTIMATE | VISION\_POSITION\_ESTIMATE | both | | MAVLink component | none | 198 | 198 | 197 | 197 | 198 + 197 | | Emission rate | none | \~30 Hz | \~30 Hz | \~30 Hz | \~30 Hz | \~30 Hz (both) | | ArduPilot EKF source | n/a | `EK3_SRC1_VELXY=5` | `EK3_SRC1_VELXY=5` | `EK3_SRC1_*=6` | `EK3_SRC1_*=6` | `EK3_SRC1_*` configurable | | PX4 EKF param | n/a | `EKF2_OF_CTRL=1` | `EKF2_OF_CTRL=1` | `EKF2_EV_CTRL` | `EKF2_EV_CTRL` | both | | Maximum altitude | n/a | rangefinder limit | barometric only | unbounded | unbounded | unbounded | | Featureless ground tolerance | n/a | low | low | n/a (forward) | n/a (forward) | medium | | Low-light tolerance | n/a | low (without IR illuminator) | low | medium | medium | medium | | Fast-yaw tolerance | n/a | medium | medium | medium-high | medium-high | medium-high | | Compute requirement | trivial | low (Pi 4B fine) | low (Pi 4B fine) | medium (NPU helps) | high (RK3582+) | high (NPU + cores) | | RAM headroom needed | \<50 MB | \<100 MB | \<100 MB | 120 to 180 MB | 250 to 350 MB | 300 to 400 MB | | Calibration required | none | sensible defaults OK | sensible defaults OK | intrinsics + extrinsics + timeshift | intrinsics + extrinsics + timeshift | intrinsics + extrinsics + timeshift | | Drone-card pill | hidden | "OF" | "OF\*" | "VIO" | "VIO" | "Hybrid" | | Estimator state | `off` | `converged` when healthy | `degraded` on static rung | `converged` after init | `converged` after init | worse-of-two | | Pre-arm gates | none | companion + flow quality + rangefinder | companion + flow quality + scale source | companion + estimator + intrinsics + extrinsics + sync + features | same as openvins | OF + VIO sets combined | ## Hardware tier guide The table below is the inverse view: pick your board, see which modes it can run. | Board | `off` | `optical_flow` | `optical_flow_degraded` | `vio_openvins` | `vio_vins_fusion` | `hybrid` | | --------------------------------- | ----- | ----------------- | ----------------------- | ------------------- | ----------------- | -------- | | Raspberry Pi 4B (BCM2711) | yes | yes | yes | marginal | no | no | | Raspberry Pi 5 (BCM2712) | yes | yes | yes | yes (NEON fallback) | marginal | marginal | | Raspberry Pi CM4 (BCM2711) | yes | yes | yes | marginal | no | no | | Raspberry Pi CM5 (BCM2712) | yes | yes | yes | yes (NEON fallback) | marginal | marginal | | Raspberry Pi Zero 2 W (BCM2710A1) | yes | yes (tier-1 only) | yes (tier-1 only) | no | no | no | | Radxa ROCK 5C Lite (RK3582) | yes | yes | yes | yes | yes | yes | | Radxa CM4 (RK3588S2) | yes | yes | yes | yes | yes | yes | | Rockchip RK3576 | yes | yes | yes | yes | yes | yes | "Marginal" means the mode runs but at reduced frame rate or with visible CPU pressure; the operator should expect tracking quality to suffer under load. ## Trade-offs **OpenVINS vs VINS-Fusion.** OpenVINS is a filter-based MSCKF; it runs lighter and recovers faster from motion. VINS-Fusion is a sliding-window bundle-adjustment estimator; it is tighter in feature-rich scenes but heavier on CPU. The default on any board with enough compute is OpenVINS; VINS-Fusion is the advanced option when the flight profile spends a lot of time in low-feature environments. **Rangefinder vs rangefinder-free OF.** With a rangefinder you get the lowest drift and the highest quality multiplier. Without one you can still fly GPS-denied but the EKF de-weights your samples and the operator-visible quality drops by roughly 40 percent on average across the scale ladder. The rangefinder is cheap insurance. **Hybrid vs single estimator.** Hybrid is the most resilient mode and the most expensive one. Two cameras, two estimators, twice the CPU. Worth it for missions that mix indoor low-altitude segments (OF strong) with corridor flight (VIO strong). Single-estimator modes are simpler and fine for most flights. ## Where to go next * [Modes](/drone-agent/vision-nav-modes) for the full per-mode reference including pre-arm matrix and fallback ladder. * [Hardware](/drone-agent/vision-nav-hardware) for tested camera and rangefinder picks. * [Features](/drone-agent/vision-nav-features) for the use cases each mode unlocks.