Imprecise GPS waypoints are causing me to CRASH!

[Ben Morehead]

Guys,

I realize that GPS waypoints are not +/- six inches, but boy is their imprecision causing me problems. I fly my drone carefully in Litchi Waypoint mode, dropping waypoints along my route. Then, when I run the mission, there are all kinds of problems:

1. Wrong track (west): It'll be too close to the building (see 19s into this video: https://www.skypixel.com/videos/5c73e9df-28fe-48b0-ba32-fb89a4eee715, if you watch closely, you'll see the video frame actually moves, because the feet of the P4 scraped across the top edge of the building -- can't get any closer to a wreck than that!).
2. Wrong height: the waypoints I set VERY carefully so that the P4 was EXACTLY at roof level, not any higher, because when it's higher, you can see all the ugly gravel on the roof, and I didn't want that to show, and not any lower, because that would cut off the pyramid. Then, when I run it, it's two feet higher than the roof, and all that ugly gravel is visible.
   
3. Wrong track (east): twice when I ran this mission, I crashed into the tree near the building (see near miss at 4s here: SkyPixel - Connecting Creativity). I was not within five feet of it when I dropped the waypoint. UGH!

So, I guess my question is: how accurate are those waypoints? Any way to make them more accurate?

Very frustrating for those of us trying to be precise with our flight paths.

BHM

 

[SpaceDan]

Did you set your waypoints based on google satellite? If I use google satellite as my reference and position the drone to fly 10 feet away along the side of a building, I would assume the tolerance is +/- 20 feet. Has anyone tested this out, to see how closely waypoints based on Google satellite match up when you fly the mission?


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[Ben Morehead]

I set them using Litchi's "Waypoint at aircraft" feature. I usually have 12 or more GPS satellites locked before I set a waypoint I just don't think the waypoints are terribly accurate.

BHM

 

[coco777]

Why do you do that ? Why not just set up the mission at your desktop on Google earth using the path tool, save the file and open it up in the Litchi Mission Hub, then check it over and set up the rest of the mission (speeds, curves, gimbal, etc), then go and test it. Don't know why your 'dropping' way points ?

 

[Ben Morehead]

Why do you do that ? Why not just set up the mission at your desktop on Google earth using the path tool, save the file and open it up in the Litchi Mission Hub, then check it over and set up the rest of the mission (speeds, curves, gimbal, etc), then go and test it. Don't know why your 'dropping' way points ?

Google Earth can't tell me how high the building is, or whether there's a newly planted tree right in my path. Seems like dropping waypoints would be more precise and safer.

BHM

 

[m0j0]

So what I'm gathering is you need the birds elevation to be accurate within 12-24 inches. Is that what you really expect? If that is what you are saying good luck with that and ..... If you are going to adjust the flight path lower to compensate for the 2 feet I would order a new bird now so that you won't be grounded too long waiting for the return of this one..


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[Ben Morehead]

So what I'm gathering is you need the birds elevation to be accurate within 12-24 inches. Is that what you really expect? If that is what you are saying good luck with that and ..... If you are going to adjust the flight path lower to compensate for the 2 feet I would order a new bird now so that you won't be grounded too long waiting for the return of this one..

I hear you. Yeah, I'm learning the limits of waypoints and what happens when you exceed those limits. It's ugly and expensive.
BHM

 

[flyboy73]

I am afraid that if you are expecting the P4, or any recreational drone, to achieve and maintain an altitude you set within + or - 2 feet, especially unobserved, you will soon be experiencing a crash. I urge you to allow more distance. These are sophisticated toys, not precise flying instruments that are totally reliable in every dimension. GPS itself is not accurate to within those distances.

 

[m0j0]

Haha.. I think the issue will come down to the barometer.. There are too many variables that will cause variances. Variances which are far greater than 24 inches.


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[SpaceDan]

If you fly to a spot, drop a waypoint there, then come back the next day and tell the phantom to fly to that waypoint: how close will it be? I'd assume it would be within 5 feet, 90% of the time. But there is the 10% of the time when it could be beyond 5 feet. Can anyone chime in on this? It's worth doing some testing.

 

[Ben Morehead]

If you fly to a spot, drop a waypoint there, then come back the next day and tell the phantom to fly to that waypoint: how close will it be? I'd assume it would be within 5 feet, 90% of the time. But there is the 10% of the time when it could be beyond 5 feet. Can anyone chime in on this? It's worth doing some testing.

This is the question I want answered! I'm thinking it's not reliable (repeatable) enough for a precise flight path (e.g., down a narrow creek with lots of foliage) . . .

Seems like GPS itself ought to be accurate to within a foot or two. . .

BHM

 

[SpaceDan]

This is the question I want answered! I'm thinking it's not reliable (repeatable) enough for a precise flight path (e.g., down a narrow creek with lots of foliage) . . .

Seems like GPS itself ought to be accurate to within a foot or two. . .

BHM

Someone needs to do some testing and prepare a report for us B-) Any volunteers? Until I get more data, I'd allow for a 10 foot buffer to avoid any collision. BTW I didn't know you could "drop" a waypoint on Litchi by flying to the spot you want and dropping it, neat feature.

The other test we need is to see how accurate google satellite images are compared to a waypoint you program --> If I program a waypoint on my computer to be 10 feet above the north-east corner of my house (based on google satellite), if I fly to the waypoint, how close will it actually be?

 

[rmfa]

I can sum this up. Is GPS this accurate? No, its not. You can see that here:

Hover Accuracy Vertical:
+/- 0.1 m (when Vision Positioning is active) or +/-0.5 m
Horizontal:
+/- 0.3 m (when Vision Positioning is active) or +/-1.5 m

DJI Phantom 4 – Specs, FAQ, Tutorials and Downloads

 

[SpaceDan]

I can sum this up. Is GPS this accurate? No, its not. You can see that here:

Hover Accuracy Vertical:
+/- 0.1 m (when Vision Positioning is active) or +/-0.5 m
Horizontal:
+/- 0.3 m (when Vision Positioning is active) or +/-1.5 m

DJI Phantom 4 – Specs, FAQ, Tutorials and Downloads

Thanks for the info. +/-0.1m vertically and +/- .03m horizontally is very accurate IMO. That's only +/- 1 foot horizontally. I wouldn't trust that I'd actually get that level of accuracy if placing a waypoint near an object (buliding, tree, etc.).

 

[IBV]

If you crash 4 times you can buy a matrice 600 with pro IMU version. That´s the right tool for what you want to achieve.

 

[Wibble]

GPS altitude is never very accurate.
Barometric altimeters need constant resetting due to changes in air pressure.
Full sized aircraft use radar altimeters!!!

 

[chazz]

Guys,

I realize that GPS waypoints are not +/- six inches, but boy is their imprecision causing me problems. I fly my drone carefully in Litchi Waypoint mode, dropping waypoints along my route. Then, when I run the mission, there are all kinds of problems:

1. Wrong track (west): It'll be too close to the building (see 19s into this video: https://www.skypixel.com/videos/5c73e9df-28fe-48b0-ba32-fb89a4eee715, if you watch closely, you'll see the video frame actually moves, because the feet of the P4 scraped across the top edge of the building -- can't get any closer to a wreck than that!).
2. Wrong height: the waypoints I set VERY carefully so that the P4 was EXACTLY at roof level, not any higher, because when it's higher, you can see all the ugly gravel on the roof, and I didn't want that to show, and not any lower, because that would cut off the pyramid. Then, when I run it, it's two feet higher than the roof, and all that ugly gravel is visible.
   
3. Wrong track (east): twice when I ran this mission, I crashed into the tree near the building (see near miss at 4s here: SkyPixel - Connecting Creativity). I was not within five feet of it when I dropped the waypoint. UGH!

So, I guess my question is: how accurate are those waypoints? Any way to make them more accurate?

Very frustrating for those of us trying to be precise with our flight paths.

BHM

Doesn't DJI Go actually have the capability of waypoints that you have to fly the bird to each location? I've never tried it or even looked at it but maybe that would be more accurate for what your doing...

 

[Ibmftw]

Strange some of the stuff in this thread, my Litchi waypoint missions seem to be reapeatedly accurate to a foot or 2 on all axis, on all dimensions.

 

[SpaceDan]

Strange some of the stuff in this thread, my Litchi waypoint missions seem to be reapeatedly accurate to a foot or 2 on all axis, on all dimensions.

how accurate is it using google satellite images to place your waypoints? thx

 

[Toyz]

Litchi waypoints are not accurate enough. They seem to be plus or minus 20 feet. Useless at closer distance. Might work for filming a waterfall at 100' away but if the subject closer up (under 40' away waypoints and heading and poi are not going to cut it.