Replies

  • We try to use ublox m8x chip to discover a base-rover trk system. and the result is good . from system on to get fix time usually use only 2min,,And wo want to provide some board for DIYs to test the system in different country.You can visit the www.i-rtk.com to submit you information for demo.

  • We did a RTK base, based on M8T for remote monitoring purposes. It includes a long range radio (>8 km with directional antennas) and solar power management (10W panel). The device can communicate each other to do a mesh network. We use the same device as base and rover and we achieved sub-centimeter (in some case sub-millimeter on 24h series) accuracy in quasi real time. RTK SW is proprietary but you can use RTKLIB for cm accuracy. We have 5 devices on a mountain in Italy since last august.

  • I'm playing around with emlid.com's stuff, the NEO-6T USB dongles. I bought two for my laptop to get started. I get fixes using very cheap antennas and I'm going to upgrade to some better ones to improve the performance. Improving the performance mostly means that the time to get a fix is reduced.

    With these not-so-good antennas, I lose the fix the moment I nudge the antenna a bit. If you look online on topics relating to RTK, RTKLib and some applications, they often state that L1+L2 is a requirement for moving vehicles... maybe it will track ok if you move slow enough. L1+L2 receivers and antennas perform much better, but immediately move out of a comfortable price range ($2k?). Good, small antennas for L1/L2 start at $350. But if you set up a base with such a system and put one on your car, it tracks really great. The reason why is that L2 provides more information to the receiver and uses a slightly different frequency as well, so that it's easier to resolve ambiguities and get the fix back (i.e., you need less time in a specific position to know where you are and this is important when you're moving at a certain speed).

    The way I see it is that L1 is good if you want a dirt-cheap solution for doing measurements in the field using static rovers and bases. So when you do surveys you can take ground control points with good accuracy too. If you don't have time to wait around for the base station's position to converge really well, you can still *use* the fixes from the rover, but the positions will all be shifted by a certain amount. However, this already helps you to provide a photo in the correct scale and the geo control points help your processing software to resolve camera parameter ambiguities, so you get better looking photos. I don't really use GPS data in camera's because the ground control method is so much better in terms of accuracy.

    Resuming: for DIY and cheap stuff, I don't think RTK works yet, because it only uses L1 band. It's possible that the piksi however greatly improved on this (uses galileo and some other satellite systems), but at the same time I haven't seen people bragging about their piksi RTK drones with super high accuracy.

    You need computer power onboard as well to process the raw data. But some modules have multiple uart's, so they can produce NMEA data on one to the AP and then raw data to the onboard computer. A very interesting project then would be to dynamically filter the two using their relative certainty. So you always fall back on the normal GPS, but when the RTK fix improves, it helps to get a better fix position. On multirotors this is probably easier, because they can hover and therefore make it less prone to errors due to the vehicle's constant velocity.

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