Source altitude displayed in MP?

[semo (sami)]

Hi all ,

I want to know what is the source for altitude in mission planner HUD

Is it GPS / Baro / something else ?

when I set the EKF2 source alt to GPS / Baro Dose it change in the HUD ?

when I move mouse in the Map in Flight plane it show the alt of home location such as 500 m ASL
BUT when gps lock the alt-asl value is about 512 mASL 0m AGL why this error and how to solve it ?

many time after power the plane alt start at 0 then move up and down even the plane not moving and sat no. 9 to 11 and HDOP 0.9

What is more accurate GPS or Baro ?

Hope any one can help with solution for these Questions ?

best regards .

[hunt0r]

I think (but have not confirmed) that MP’s HUD value is the calculated output from the AHRS system. (This should be an EKF, unless something has gone wrong, and some other value is being used instead) This will be the most accurate calculation available to the system and the one it uses to make flight decisions.

In my experience, altitude measurement based on a barometer is much better than altitude via GPS. There are details and caveats to this, but I think they’re not too important.

Does this answer your questions?

[semo (sami)]

hi @hunt0r you give some info but not clear yet .

How I can figure the different between baro and GPS alt ?

where is the problem in different alt in ground as question above ?

[hunt0r]

I’m sorry, I don’t understand what you’re asking.

Baro altitude is calculated using a barometer. GPS altitude is a part of GPS measurements. Because they are fundamentally separate sensors of the same quantity (altitude) they will report different values. I believe you can select which one the EKF uses. I recommend Baro, in my experience it is more accurate than GPS altitude.

[semo (sami)]

@hunt0r good info ,

Now ,

Question 1 : the alt value shown in HUD , Is it GPS or Baro , or Depend on what I set in EKF ?

Question 2 :

in the Quick tab I set all the Alt value I think it’s GPS Alt , if so ,

Where is the Baro alt value ?

The purpose of this, I want to know the difference in value between GPS Alt vs Baro Alt

Please forgive me if I can’t come up with the idea

Regards.

[hunt0r]

@semo

Question 1 : the alt value shown in HUD , Is it GPS or Baro , or Depend on what I set in EKF ?

@hunt0r

I think (but have not confirmed) that MP’s HUD value is the calculated output from the AHRS system.

@semo

The purpose of this, I want to know the difference in value between GPS Alt vs Baro Alt

@hunt0r

Baro altitude is calculated using a barometer. GPS altitude is a part of GPS measurements. Because they are fundamentally separate sensors of the same quantity (altitude) they will report different values.

It looks like I have answered both of your questions. If not, could you help me understand what you are asking?

[semo (sami)]

the first question is answered thanks a lot ,

the 2nd not yet

I meant i want to read instance value during flight like this ,
Baro alt = 250 m
GPS alt = 255 m

So I can Figure the difference

[hunt0r]

Ah, I think I understand. I believe you are asking “Is there a place in Mission Planner where I can read the GPS Altitude and the Baro Altitude during flight?”

I would look at the “Status” tab of Mission Planner and see if that data is displayed there.

I am not sure, and don’t have MP in front of me. Can anyone else confirm that’s correct (or wrong?), or suggest something else to try?

[semo (sami)]

Yes that’s what I meant .
until any one confirm I have last question .

when I power on the plane in the ground displayed alt in HUD start at 0 then move up and down even the plane not moving and sat no. 9 to 11 and HDOP 0.9 why ??

Coz it make problem for me in this scenario :

Plane in ground, alt = -120 ( sure it’s error )
takeoff and alt keep changes from the value -120
fly some time
when landing I need the alt for the plane , real alt was about 50 m but MP read alt -70 .

hope you got the idea .

[hunt0r]

To make sure I understand correctly, I’ll re-state your issue:
“When you power on your plane and leave it sitting still on the ground, the altitude in MP starts at zero but drifts as far as -120m.” This (of course) leads to incorrect altitude being displayed in MP when you begin flying.

If I understand the problem correctly, here is my best advice:

1. Set your EKF2 source alt to Baro, if it is not already.
2. If you have done this, and your altitude is drifting to -120m without the plane moving, something is definitely wrong.

A DataFlash log would help us diagnose the problem, but to record it, you need first to set the parameter LOG_DISARMED = 1, and then send us a log demonstrating the altitude-drift problem.