Pre-Arm Safety Check issue: Need 3D fix

[MAZE Alexandre]

Hi everyone,

We are trying to use the 3dr x8+ (ArduCopter V3.1.0 Quad) for a simple use without GPS.
We are having an error on the HUD on Mission Planner: "Need 3D Fix".
We don't know what does that mean and neither why we have this error.
It's maybe linked with the GPS use, but because we don't need it can we get rid of it, and the most important, how can we do so?

Thank you for your answers.

Cheers,

Alex