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Testing Procedures for Legacy GPS Gear for Week Rollover on April 6-7
I’ve been considering what would make a good test to verify that my four Leica SR530 receivers will be able to handle the GPS week rollover on April 7, 2019. I came up with two test procedures.
Prior to the tests I’ll collect 4 hours of static data on two points near my domicile and process them with OPUS/OPUS Projects. In the wee hours of April 7 I’ll set up on those two control points and start collecting static data at 4:30 a.m. MDT.
If my calculations are correct the GPS week rollover will occur at 6:59:41 a.m. MDT to account for the 19 seconds between GPS time and UTC time. I will let one of my receivers run without interruption until 10:00 a.m. The other receiver I’ll stop at 6:58:40 a.m. and store the results, then occupy the point again starting at 7:00:40 a.m.
My LGO software allows the user to merge two data files at the same point (same point ID too) as long as the end time and start time are within 30 minutes. This should allow me to see if there is any time problem when I import the data.
It may be that the receiver that I run continuously until 10:00 a.m. will suffer an error and not be able to store the data. The other receiver may log and store the early data and fail to log anything after the rollover. If this happens it may be due to the almanac in the receiver not being up to date.
I usually collect static data at 5 sec. epochs so I can post-process in LGO. For this exercise I will log data at 1 sec. epochs just to see what happens at the rollover.
My SR530 receivers were manufactured in 1999, 2000 and 2001 and have the latest firmware (ver. 5.1) that fixed a problem in 2009.
Any suggestions on improving my test procedure or alternatives are certainly welcome. It may be that things won’t work correctly until the receivers have downloaded almanacs with dates after the rollover.
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18 Replies
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Sounds like you have thought through your procedure carefully.
But doesnt the rollover happen at 2359:42 UTC ? That’s evening April 6 in the US.
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Thanks Bill. My senior moments used to be only lapses in memory. Now I see they include basic arithmetic…..SIGH! Maybe I should retire along with my old legacy Leica gear.
Note to self: MDT is -6:00 hours from UTC, not +7:00 hours. Making the start time 3:30 p.m. April 6 will work a lot better than scaring the neighborhood raccoons at 4:30 a.m. the next morning.
ETA: More arithmetic corrections….need caffeinated beverage.
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MST is -7, MDT -6 so the rollover is about 6 pm MDT. I didn’t consider how much lead time you need.
I took some data last week and the RINEX files say 18 leap seconds, not 19.
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Bill,
With my repeated public demonstration at math wizardry, I’ve probably misapplied the leap seconds correction too, also.
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I don’t think that the ability to span the rollover event is particularly important, I’m interested in learning whether or not my receivers will be functional after the event. My test procedure won’t require getting up at an ungodly hour!
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Since you are not doing a project on the afternoon of the 6, continuity is not important. Collect 4 hours before 0:00 UTC and 4 hours after, either it works or it doesn’t work. Not much you can do about it until you know it does not work.
Paul in PA
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I tend to agree with Jim.
It’s not the ability to roll through the change. But, to run properly, on both sides!
N
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Jim and Nate,
While I agree that collecting data before the event isn’t that important, I’m interested in seeing what happens (also why I will collect data at 1 sec. epochs). And after Bill so kindly pointed out my arithmetic errors I won’t have to get up extra early, I’ll start the receivers at 3:30 p.m. and end my experiment around 8:30 or 9:00 p.m.
Starting before the rollover will also allow me to see the RINEX data and how “things” were handled during rollover. If the time stamp does go back to 1980 or 1999 I just might be able to figure out how to modify a RINEX file after April 7 to keep my Leica gear from being boat anchors. I read somewhere that rollover problems might continue until the receiver has an almanac dated after the rollover. I don’t know if that is true or not, but I did get a note from the local Leica dealer saying that I might need to reformat the system to pick up a new almanac.
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Won’t the almanac update during your long session without any other action? I thought receivers got an update multiple times per hour.
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This thread reminds me of my test of running a session through a leap second. The receiver didn’t figure it out. And I started it, left home for a party, and came back to find the battery run fully down and therefore frozen. Not good for SLA batteries, and it went downhill fast on subsequent uses.
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I just might be able to figure out how to modify a RINEX file after April 7 to keep my Leica gear from being boat anchors.
I think you can do this with teqc by explicitly specifying the GPS week number.
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From my understanding, the almanac isn’t updated multiple times every hour. It takes a little over 12 minutes to download the almanac, but it can be used for a while. My dealer suggested reformatting the system after April 7 so that a new almanac will automatically be downloaded.
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If necessary, I’m hoping that TECQ will correct the time stamp. I guess I’m intellectually curious as to what will actually happen during the rollover. The extra collection time on a Saturday afternoon will not be a bother.
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I will be watching to see what happens. We still have 530’s two of which we still use for RTK. Great hardware and firmware. We still use LGO. I have had problems with reformatting and with a corrupt flash memory. Leica’s John Essig in their Virginia tech service office bailed me out with maybe a 5 or 10 minute keystroke process – still not sure what he did but he said they do not support the 530 any more.
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Hey Jim, weren’t you involved with the “Fix Week” patch for Trimble receivers? Isn’t this the same problem?
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Hey Jim, weren’t you involved with the “Fix Week” patch for Trimble receivers?
I wasn’t involved in that effort, but I had a similar problem with some old Topcon receivers that used Trimble boards similar to the 4700. I wrote some custom software to deal with that. It does, indeed, sound like the same issue.
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This is what Trimble has on it’s website: http://trl.trimble.com/docushare/dsweb/Get/Document-808659/SuppNote – Trimble 4700 and 4800 GPS
It may work for all the legacy receivers.
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Any update on how the Leica 530’s handled the rollover week? I have a job coming up where RTN with the GS14 may not be an option due to spotty cell coverage. I may need to bust out the trusty old base and rover setup.
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Can’t talk about Leica, but my ancients are still trundling out accurate, repeatably, measurements.
For years I’ve run Sokkia RTK, base Radian, rover 2650LB.
Taken them out twice since the doomsday event and they haven’t complained.
My first trial seemed to take little longer to initialise but that could have been imagination.
Don’t post process. Log 2 minute observations in SurvCe, repeat such several times, come back later to check.
I mainly use them for cadastral control.
Happy all round here.
Apologies of double line spacing That’s outside my control
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