AHRS waiting for home despite low GPS HDOP and 10 sat count?

ArduCopter
1

Kindly do help anyone knows what could be the reasons why I got 10 sat count. <1.5 HDOP in fact 0.9-1.2 but yet I kept getting waiting for home?

2

Sat count and HDOP are important but do not tell how accurate the position is.
Those metrics were relevant 10 years ago when we had no other, but nowadays there are better metrics and AduPilot uses them.

Position accuracy is seen on the accuracy value metric (yes that one exists), and you should take a look at that one instead.

But that is also not the most important, the variance of the position also needs to be low.

If ArduPilot would allow you to take off with an incorrect home, you would certainly be surprised when later, during RTL, it would land in a completely different place from where it started. Endangering you and your vehicle.

So that is why it is waiting for a good result with good accuracy and low variance. And you are looking at the wrong metrics sat count and HDOP

1 Like
3

Thanks, Iā€™m not sure if its because I am using an internal gps. Could magnetic interference be a comtributing factor?

Anyway to disable this? I only need a rough location like <3m

4

Magnetic interference causes orientation and attitude uncertainty, but not position uncertainty. At least not directly.

Trying to disable this increases the probability of crashing the vehicle and having unexpected behavior.

Lots of people do ask how to improve the performance and accuracy of their vehicles. You are the first one asking how to degrade it. Sorry, I do not have an answer for that.

5

Problem is I check with gps software ucenter, the antenna gives good position, so does it show on mission planner. Puzzle why it kept giving this problem.

6

What is an internal GPS?

7

M10Q 5883 matek gnss

8

But it is not giving good position is it? It it would be giving good position you would have not this problem.

So your hypothesis ucenter good position is flawed. Did you looked at accuracy and variance metrics in ucenter?

9

It has only 1.2hdop pf course have good position. I suspect there are high fluctuations because hdop is flickering. I do more test isolating the antenna and keep updated.

10

HDOP is not a metric for position accuracy, is a metric for satellite constellation dispersion. read more about it on wikipedia.

11

That is why I am puzzled. The gnss has this blinking light as well which indicated a gps fixed. But still comes with this error. Sometimes it just work. Sometime for 5 to 10 mins is the same waiting for home. At times it came with the error mag field. Sometime gps glitch compass error etc.
This gnss really is quite bad.

12

I concluded maybe its just not a very good hardware.

13

Something is just wrong. I check the fluctuations is in less than 1 metre. I still get Waiting for Home. How accurate do you need it to be? Sometime we just need to to fly back to where we are within 2 metres.

There should be an option to dull down this.

14

There are a handful of metrics used to determine valid/healthy GPS. A large fluctuation in message rate could also cause problems, along with high HDOP or big step changes in position. Satellite count is largely irrelevant, though a low count is indicative of poor reception. A log might help.