Hacker News Reader

Comment by joezydeco | Hacker News Reader

But it also doesn’t work well over water yet because of reflected GPS signals (Disney has been running trials on it).

Fireworks also work better in rainy/windy conditions.

It's surprising that GPS signals are that important to these displays. I figured they use GPS to provide a rough center of the display, for the "leader" drone, and the other drones would position themselves relative to their leader using some local peer-to-peer positioning signals.

Then again, I know nothing about this.

GPS + accelerometers in fusion are accurate enough, and what you describe AFAIK doesn't exist in off-the-shelf variant, which is usually the core consideration.

Drones like this use DGPS. GPS is inherently inaccurate when you need centimeter level precision, especially with spinny bladed machines in formation. DGPS uses a ground station that helps the drones gain the accuracy they need, but it's much more complex than a simple GPS unit.

I suspect the specific implementation here uses "carrier-phase RTK" which means the recievers are locking into the pure sinusoid of the carrier frequency to get sub-centimeter positioning accuracy. It's mind blowing that this works at all, given that it really isn't how the GPS system was designed to be used.

Surely drones do not need DGPS unless they need precise location against the ground.

For swarms, drones need precise location relative to each other, for which there are other techniques than GPS.

I think you are speculating - or do you have information showing that these drones use DGPS for this display?

Citation?

As someone who knows a fair amount about the underlying mechanics behind how GPS signals work, it sounds like you are misinformed. That said, never wise to assume, so I’m happy to be proven wrong.

This was my source.

https://twitter.com/wdwbusdriver/status/1184643020894953473

Especially this comment in regards to why Disney didn't take the 2016 trial at Disney Springs to completion at a larger park, like EPCOT:

"I was there when they did the Springs show. The techs told us the biggest issue the drones have is navigating over reflective surfaces (aka water). It messes with the GPS that designates their point in the formation. It would have been perfect if it wasn't for the lagoon."

The ones I saw worked just fine over a lake, and it was windy. I saw a few drift off and self-correct very quickly so it looks like they have this figured out. I assume they hold their position relative to one or more ground units.

Reply on news.ycombinator.com