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
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 | 10 Hz | 10 Hz | 30 Hz | 30 Hz | 10 Hz + 30 Hz |
| 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 |
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 robust 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 for the full per-mode
reference including pre-arm matrix and fallback ladder.
- Hardware for tested camera and
rangefinder picks.
- Features for the use cases each
mode unlocks.
