PX4FirmwarePlugin: use correct unset param1

[julianoes]

Description

NAV_TAKEOFF param1 allows to set the minimum pitch. Generally, when not setting a param it should be set to NAN or 0. The sentinel value -1 is not in the spec.

Note that this value is not used in PX4 anyway.

Also, unused param2 can be NAN instead of 0 which is generally preferred.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Refactoring (no functional changes)
• CI/Build changes
• Other

Testing

• Tested locally
• Added/updated unit tests
• Tested with simulator (SITL)
• Tested with hardware

Platforms Tested

• Linux
• Windows
• macOS
• Android
• iOS

Flight Stacks Tested

• PX4
• ArduPilot

Screenshots

Checklist

• I have read the Contribution Guidelines
• I have read the Code of Conduct
• My code follows the project's coding standards
• I have added tests that prove my fix/feature works
• New and existing unit tests pass locally

Related Issues

PX4/PX4-Autopilot#27899

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By submitting this pull request, I confirm that my contribution is made under the terms of the project's dual license (Apache 2.0 and GPL v3).

[julianoes]

Testing pending Qt download...

[julianoes]

PX4 SITL tested.

[github-actions]

Build Results

Platform Status

Platform	Status	Details
Linux	Passed	View
Windows	Passed	View
MacOS	Passed	View
Android	Passed	View

All builds passed.

Pre-commit

Check	Status	Details
pre-commit	Failed (non-blocking)	View

Pre-commit hooks: 0 passed, 0 failed, 0 skipped.

Test Results

linux-coverage-integration: 27 passed, 0 skipped
linux-coverage-unit: 105 passed, 0 skipped
Total: 132 passed, 0 skipped

Code Coverage

Coverage	Baseline	Change
66.5%	66.6%	-0.0%

Artifact Sizes

Artifact	Size	Δ from master
QGroundControl	221.84 MB	-4.47 MB (decrease)
QGroundControl-aarch64	179.43 MB	No change
QGroundControl-installer-AMD64	138.39 MB	+0.01 MB (increase)
QGroundControl-installer-AMD64-ARM64	80.66 MB	-0.00 MB (decrease)
QGroundControl-installer-ARM64	109.21 MB	+0.00 MB (increase)
QGroundControl-linux	87.09 MB	-78.80 MB (decrease)
QGroundControl-mac	87.09 MB	No change
QGroundControl-windows	86.15 MB	No change
QGroundControl-x86_64	191.65 MB	+0.00 MB (increase)
Total size decreased by 83.26 MB

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_{Updated: 2026-07-15 03:48:42 UTC • Commit: 6637cbc • Triggered by: Linux}

[DonLakeFlyer]

@hamishwillee Mavlink spec says nothing about how to deal with not passing various MAV_CMD_NAV_TAKEOFF params. Is there really a spec that says NAN is always not used. If so, I believe ardupilot tends to puke on NAN in various commands.

@julianoes Is this fact in px4 firmware side version agnostic? Not something that change somewhere along the way?

[julianoes]

I believe ardupilot tends to puke on NAN in various commands.

It used to but that's mostly fixed up by now. In this case that doesn't matter as this is the PX4 plugin.

We started rejecting invalid commands on the PX4 side which triggered QGC takeoff to fail. So obviously we had to revert the strict check on the PX4 side. However, instead of just ignoring that QGC sends something non-compliant, I opted to fix it.