Hi Ok, for survey work there *is* an alternative. It takes care of the location of the “rover” as well as the time. uBlox has a ZED-F9P module for around $100 that will do the trick. It is L1/L2, but the cost penalty isn’t all that great in this case. I don’t know if that would be a practical thing in this case or not ( = if the entire budget is $20 …. it’s not).
Bob > On Dec 3, 2019, at 3:05 AM, Anton Strydom <[email protected]> wrote: > > Hi Tom > > Thank you for all your input thus far it is appreciated > > The "CLOUD" I am talking about is a Point Cloud and I am attaching an > example for your perusal. > > I am also attaching a screengrab of a real time stereo video where you can > see the misalignment of the images > > Presently the system is purely experimental and has to be real time. > > Post processing is done to forecast possible movement and once a "trend" > has been established it can be accelerated over time using the point cloud > 3D model and the mesh it is built on > > The points monitored (targets) are surveyed in points as are the camera > placements > > Using a combination of OpenCV and Tensor Flow a number of observations and > precise measurements are possible thus allowing modeling of the structure > over accelerated time using the movement data collected from the structure > etc etc. > > Yours sincerely > > Anton > > On Tue, Dec 3, 2019 at 9:00 AM Tom Van Baak <[email protected]> wrote: > >> Hi Anton, >> >>> My question is what good synchronization of a gps clock in Nano seconds? >> >> That's not much to go on; there are so many variables. To start with, >> almost any cheap eBay GPS/1PPS receiver these days will give you time to >> within a couple 100 ns with no special effort on your part. >> >> If you have a fixed location, a good antenna, a clear view of sky, a >> modern GPS receiver with 1PPS output, and have the ability to apply >> sawtooth correction in h/w or s/w, then you can probably get within 10 >> ns. Many commercial and DIY GPSDO are based on this assumption. >> >> Note that this "10 ns" is relative timing. To obtain 10 ns absolute UTC >> is much harder because you have to calibrate and compensate for antenna >> delay, amplifier delay, cable and connector delay, receiver delay, 1PPS >> buffer amplifier, output cable, and edge detection delay, etc. So almost >> nobody can do absolute timing on the cheap. >> >> Fortunately for many applications (e.g., GPSDO) it's not necessary >> because most of those fixed phase corrections cancel. >> >> Then there's the question if your application is based on a surveyed >> fixed location -- if static, or ground mobile, or airborne. Do you have >> any size, mass, or power constraints? Do you need a local oscillator / >> time base or is this just raw, live 1PPS ticks from the receiver? Do you >> need good results now in real-time or can you wait a day or a week to >> get better results after some post-processing? >> >> So the rough answer is that these days 100 ns is easy for under $50; 10 >> ns is possible for under $500; and 1 ns absolute is near impossible >> unless you have a lot of development time and money, not to mention >> atomic clocks and test equipment to validate that extreme level of >> performance. Plus the expense of trip(s) to your national NMI for UTC >> calibration at the ns level. >> >> Does that help? If not, can you summarized your technical requirements >> in more detail for the group? There are a number of people on the >> mailing list who have done recent measurements using the ublox F9-series >> receivers and those results should be helpful in your quest. >> >> Precise timing and 3D imaging sounds like an interesting application. >> You mention clouds though; do they move fast enough that milliseconds or >> nanoseconds matter? Can we see your math? I'm curious but confused. For >> example, nanoseconds matter for triangulation of high energy atmospheric >> cosmic rays, but I've not heard where nanoseconds matter for >> photogrammetry. >> >> /tvb >> >> >> >> On 12/2/2019 12:01 AM, Anton Strydom wrote: >>> Good day All >>> >>> I am new here. >>> >>> I have been busy with GPS systems for the last couple of years and have >>> also developed a number of low cost high accuracy L1 units. >>> >>> I also play around with photography and especially in the field of >>> photogrammetry and 3D point cloud situations. >>> >>> Time being the one thing that influences everything to do with accuracy. >>> >>> My question is what good synchronization of a gps clock in Nano seconds? >>> >>> Obviously the closer to 0 the better I would guess. >>> >>> Thank you in advance >>> >>> Yours sincerely >>> >>> Anton Strydom >>> _______________________________________________ >>> time-nuts mailing list [email protected] >>> To unsubscribe, go tohttp:// >> lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>> and follow the instructions there. >>> >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. >> > <cuprusreport.pdf><stereoscreengrab.JPG>_______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
