Estimating Flight Height Above Ground with ctmm — Best Practices?

[lisa king]

Hi Chris,

First off, thank you for such a well-documented and powerful package. I've been using ctmm to explore GPS data from our bat tracking projects and it's been incredibly helpful.

I'm currently trying to estimate flight height above ground (i.e., GPS altitude minus terrain elevation), but I'm running into challenges due to uncertainty in both telemetry and terrain data. Unfortunately, this is compounded by not being able to estimate UERE from tag calibration data (different tag settings to the survey data).

I’ve tried two approaches:

1. Modeling flight height directly as GPS altitude – terrain height, but this often yields negative values — likely because only telemetry error is accounted for.
2. Modeling GPS altitude and subtracting terrain height from the point estimates, but this still contains error from multiple sources and results in negative flight heights.

Is there a recommended best practice for handling this within ctmm? Or would I need to resort to a more customized method that accounts for terrain uncertainty — something I’d prefer to avoid due to time constraints?

Any guidance or suggestions would be greatly appreciated!

Thanks again for all your work on ctmm.

Best, Lisa