Via Hackaday:
Where most GPS receivers only look at the data coming from the GPS satellites orbiting overhead, the Piksi uses another technique, real-time kinematics (RTK), to determine the receiver’s location with exacting precision. The basic idea behind RTK is to look at the carrier frequency of the GPS signals at 1575.42 MHz. This frequency has a wavelength of 19 cm, compared to the alternating 1s and 0s of the that are transmitted at around 1 MHz, or about 300 meters between each bit. While centimeter-level precision isn’t possible with only one receiver, two of these Piksi boards – one base station and one on a vehicle, connected via radio link – can make for a very exacting high-accuracy GPS receiver.
Comments
@Grant.. at the end of the day you will need to stitch imagery together into one large image that includes your entire area of interest. Overlapping would be required in order for any stitching algorithm to find the similarities and stitch lines. I consider writing a tool to aid in stitching but it seems like there are quite a number of choices for doing it and my time better spent elsewhere. Agisoft does it pretty well but is quite expensive and processor intensive... but you do get nice output from the tool after waiting quite some time. I have heard of people using Microsoft ICE to stitch, but haven't tried that myself.. I think if you did that you would need some helper tool to auto rotate the images to the same orientation and order them based on closest and most over lap order... not just the order they were taken.
While I maybe skeptical about the RTK GPS, the idea of an open source FPGA GPS is cool enough that I am personally a backer of this project and look forward to playing with my unit.
Paul
General comment...
For RTK to work you need two receivers. The accuracy is established between the two receivers, so if both are moving it would enable precision formation but would do NOTHING for accuracy of the two receivers with respect to the outside world. Ibn order to get RTK levels of accuracy one of the receivers needs to be fixed in a known position. The accuracy of the rover position is going to be dependant on the accuracy of the fixed position....
Also I had some very expensive (>$1K L1 RTK gps recievers with 20Hz updates that I was never able to get working on a helicopter. The helicopter vibration killed the RTK solution as soon as the blades started turning.
I'm a tiny bit skeptical that this is going to work well on a quad with just L1 GPs.
The real expensive Ag RTK GPS systems use both L1 and L2 frequencies and due to the carrier phase difference between the frequencies (called the wide lane) the carrier phase ambiguity is greatly reduced causing them to be much more reliable. While the 1K L1 RTK GPS units never worked on the helicopter, the >5K$ L1/L2 RTK GPS units worked flawlessly.
Monroe, My guess is your radio sondes read psuedo range and carrier phase, not raw GPS.....
The remote s/w is managing orbits etc...and solving for position.
The 4G lockout limit in commercial GPS is not in this part of the code, the 4G limit is inherent in the psuedo range tracking loop. So your radio sonde will most likely not handle any more G's than a normal GPS. So if you are looking for this to solve your rocket GPS problem its likely not going to work. Niether is the GPS thats the subject of this post. Given that you can probably modify the GPS that is subject of this post to open up the tracking loops sacraficing precision to get a wider G range.....
Yeah I think the application is very interesting.. is 900 for the package or just the receiver?
There is quite a few things that I could see this coming in very handy.. since I am working on remote sensing software with my software tool AgPixel.. something that I would like to be able to do is have a receiver like this with a laptop where the end user could use the VI map or any other sort of map they generate in the tool and then use a receiver like this to pinpoint certain things that show up in the imagery or reverse.. use it to pin point issue items and do some sort of supervised classification technique. Or in the initial setup establishing ground control points to geo reference the imagery... sort of a one time survey of each field.
Usage/Application in Ag: RTK with a fixed base station that never moves gives you both accuracy and precision.
Precision=no drift, so when I set my tractor to drive on 120 foot centers while spraying expensive chemicals, it will always have the next pass be 120 feet over, with no overlap or misses. With normal GPS, depending on the day the signal can drift 6inches to 2 feet.
Accuracy = repeatablility. Every time I come to the field, without moving my GPS markers in my tractors computer I will drive on exactly the same tracks, minimizing crop damage.
Maybe I mixed Accuracy and Precision up, but you get the idea. Having a base station that doesn't move during the application (like on a tripod at the flying field) will give you no GPS drift, so you have relative position accuracy (and with 4cm accuracy?!?!?! yay!) Having a base station that never ever moves, gives you repeatability over time. Having a base station that never moves, AND if it has it's actual GPS coordinates hard-coded into it will give you absolute accuracy and precision and happy dreams about flying bunnies!
LanMark, you are exactly right, this is VERY exciting for Ag. Last time we priced out RTK for our tractor fleet the John Deere dealer wanted $18,000 to set up a base station on our farm, and around $10,000 per tractor to set them up with the RTK radios and other hardware (not including the steering valves and computers that are already on the tractors.
Our tractors can take like 15 different forms of GPS data inputs, so hopefully without much tinkering we can just feed data from these new boards into the existing autosteering computers. Build a base station with a powerful transmitter that can cover the whole farm and we'd have RTK for next to nothing. This is VERY exciting. Surveying for drainage and other stuff is another application with a small handheld receiver and a base station on a tripod.
Maybe we'll start up a side business of installing RTK systems for other farms in the area. Could charge 1/10th of what the dealers charge and still make money.. hmm.. or maybe chard 1/2 or 1/3 of what the dealers charge.. hmm...... :) Super exciting stuff in any case!
The problem with carrier phase acquisition is phase jumps. It needs a very fast acquisition rate (100 Hz or more) to avoid phase jumps on a fast moving copters. I'm not sure that RTK can work on a copter with 10 Hz or less acquisition rate.
Multipathing is a big problem too at the carrier level.
Before to spend large amount of time trying to make it works, it's important to check that the acquisition rate is fast enough to perform correctly in the difficult copter conditions (fast fly and banking antenna).
Olivier.
Did'nt anyone notice we broke this 24 hours early at sUAS News....
-
1
-
2
-
3
of 3 Next