# VIO altitude estimation error

Source: https://forum.modalai.com/topic/215/vio-altitude-estimation-error
Category: General Questions (https://forum.modalai.com/category/2/general-questions)
Posted: 2021-04-29 13:09:18 UTC by vmassague
Replies: 1 · Views: 734

## vmassague · 2021-04-29 13:09:18 UTC

Hello Everyone,

**Problem:** During an autonomous mission outdoor, VIO failed to estimate the correct altitude of the copter. VIO was estimating an altitude of around 1.5-2.5 meters while it was ~4.5 meters in reality.

**I am using the following hardware:**

ModalAI m500 with no hardware modifications 

**Log file:** 
https://review.px4.io/plot_app?log=24a66118-0151-4b7a-9477-0858c375fc88

**Relevant Parameters:**

EKF2_AID_MASK = 1 (GPS only)
EKF2_HGT_MODE = vision (using VIO/Tracking camera)

**My Observations:**

The drone took off more aggressively than usual, which probably caused some confusion in the VIO altitude estimation. 

Hope someone can help.

Victor

## Reply by Chad Sweet (ModalAI staff) · 2021-04-29 15:59:44 UTC

It is likely there were not stable visual features on takeoff. A field of grass is not that great for visual feature tracking. You could try putting something in front of the drone on the ground for it to look at and see if that helps