Way point missions- gps accuracy

[Hayabusa]

I set up a way point mission on Litchi. It was about a 3-4 mike round trip so at one point it does disconnect but continues and completes mission as it is as set.
After viewing the video, I came puckering close to a tower on this island, and a hi ruse building. Now in reality, I was probably a safe distance away but looked awefully close.
My question is, now that I have this and many other missions saved. Can or does the gps coordinates change at all? Meaning If I send it back on the same exact mission without any changes, would it be the exact same run or do satellites move so that now my flight path could be slightly altered?
I would hate to make a safe run one day, and the next it doesn’t return because it flew into something because now a satellite was off by x amount.
One reason I want to know is because I set up a few good missions that I want my daughter and friends to sit back on my balcony and enjoy a birds eye view of some cool sites. Just want to make sure tonight’s tour would be the exact same as last nights. Lol
Thanks
Mike

 

[sar104]

The coordinates of fixed points on the ground do not change with time. The accuracy of a GPS position estimate does change, but for a receiver with a good view of the sky (e.g. an airborne Mavic) the position should be good to within 5 m or so, and often better than that.

 

[BigAl07]

We usually "assume" a 10M variance and build that into the flight plan.

 

[sar104]

We usually "assume" a 10M variance and build that into the flight plan.

That's a good conservative approach.

 

[BigAl07]

That's a good conservative approach.

You know me too well LOL. I'm conservative as they come and always try to err WAY on the good side of caution.

 

[Hayabusa]

The coordinates of fixed points on the ground do not change with time. The accuracy of a GPS position estimate does change, but for a receiver with a good view of the sky (e.g. an airborne Mavic) the position should be good to within 5 m or so, and often better than that.

This is good to know but now thinking about it. With what your saying then is even when I planned my mission and flew it for 1st time, just because I’m clearing something on the map. Doesn’t necessarily mean I will clear it in reality with a possible 10’-20’ variance. I just got lucky and now understand why on my mission, it looked fine on the map when I planned it and I had plenty of space between the ac and any object. Right up till I flew it and at 2 points, I came closer than I thought it should.
I will now plan better.
Would this apply to height or is that read off something else. I did plan for a bit higher than I thought but seemed lower and closer than what so thought it should have been. Could have been camera angle as well. At one point I thought I was litteraly flying into a building, I even tried to start going up to miss it and then the ac started turning towards next waypoint and camera adjusted and I saw I was actually a good distance always. Scared me good thow.
Thanks all
Mike

 

[sar104]

This is good to know but now thinking about it. With what your saying then is even when I planned my mission and flew it for 1st time, just because I’m clearing something on the map. Doesn’t necessarily mean I will clear it in reality with a possible 10’-20’ variance. I just got lucky and now understand why on my mission, it looked fine on the map when I planned it and I had plenty of space between the ac and any object. Right up till I flew it and at 2 points, I came closer than I thought it should.
I will now plan better.
Would this apply to height or is that read off something else. I did plan for a bit higher than I thought but seemed lower and closer than what so thought it should have been. Could have been camera angle as well. At one point I thought I was litteraly flying into a building, I even tried to start going up to miss it and then the ac started turning towards next waypoint and camera adjusted and I saw I was actually a good distance always. Scared me good thow.
Thanks all
Mike

Flight altitude is primarily determined barometrically, relative to the take off point. That accuracy can vary too, by up to several m, over the course of a flight.

 

[Hayabusa]

Flight altitude is primarily determined barometrically, relative to the take off point. That accuracy can vary too, by up to several m, over the course of a flight.

Thank you

 

[Mossiback]

Be mindful of the expected winds aloft. A 3-4 mile round trip doesn't leave much room for error and a strong enough headwind will actually make it fly backwards.

 

[53-63-6f-74-74]

Also keep in mind that Google's orthographic photos (which are used in the Litchi app and hub) are not 100 percent accurate with respect to horizontal placement, and are even worse in the vertical. In my part of the world Google imagery has a horizontal error of 6-10 feet. I know this from using ground control points on a regular basis.

 

[BigAl07]

Also keep in mind that Google's orthographic photos (which are used in the Litchi app and hub) are not 100 percent accurate with respect to horizontal placement, and are even worse in the vertical. In my part of the world Google imagery has a horizontal error of 6-10 feet. I know this from using ground control points on a regular basis.

Exactly.

We do a lot of "Construction Documentation" and I like to roughly fly the site "virtually" before we ever go on site. I'm surprised at the variations we see from the Google Earth images. One job site I did a flight "virtually" and it was flawless. Got to the jobsite and the foundation was "in the road" of the GE image (about 10' off). In order to be very accurate I finally found a way to overlay one of my images on the GE layer and then was able to pre-plan future flights that have worked flawlessly the first time I actually flew them.