Being somewhat behind in our work schedule all of a sudden, we decided to try S&G on a 5-6 acre topo job, using 2 rovers. When things go right (or should I say perfect) we can run 2 rovers on these type sites and cover about 25-30% more ground than when conventional. Yesterday I did a Mission Planning session for today's attempt, and we isolated a 1 hour spike in the morning, and a 1 hour spike in the afternoon. We decided to wait on beginning our data collection until after the a.m. spike, as we had other thing we could do. Knowing the way the firmware handles point I.D.'s, and that we would be constantly having to "over write" point I.D.'s, we decided to do a clear memory. Then, we turned on the units, did a fresh initialization, and waited until the units (in Navigation mode) fixed a position and had WAAS correction. We had a pair of L1/L2 units on site for base units (will only process to one - the other was purely for backup), and initialized both PM2 rovers on points within 10 feet of the base units. So far, nothing in the routine really should have any bearing on the problem we experienced.

After initializing the PM2's, we noticed that both the L1/L2 units (yellow bricks) were logging 8-9 sv's, and the PM2's only 6. I do have the yellow units set to log 5° mask, so that is partially understandable. But, as the project progressed, we should have been logging more sv's with the PM2 units, and very shortly into the project, still showing 6 sv's, we were "losing lock". One unit had to re-initialize a couple of times, the other lasted until just before the afternoon pdop spike. We shut down all the units for an hour to do other conventional work, and when returning to the units, the yellows were logging 9-10, and the PM2's still only 6. BUT....when you view the SV availability page, at least 8 satellites show up as fully locked, but the "survey" page shows only recordinig 6.

This was mostly in a very gps friendly location, which we have very little of and really appreciate the few opportunities we have to use S&G or rolling Kinematic.

I have not downloaded the files yet, so I still do not knnow if the entire day was a waste or not. This has happened several times before, and we're just totally baffled by the disparity between the different unit's logging capabilities.

Is it firmware, or do the old units just need some tonic?

jd

Sounds like your day was kinda like mine going round and round with SurvCE and the RTK rig(s).

Dangerous Dave

J.D.

31 is still out of service. It is probably done for the count.

25 went on the fritz today. If you had 6 GPS, you had them all. Sometimes only 5 were there and for about a 1/2 hour only 4.

Can that yellow stuff pull in satellites that are not there, or was it speaking Russian?

I get NANUs and a daily status report. It is very seldom I even go to the navcenter site anymore.Better sign up today.

Paul in PA

I just finished downloading all the files, and they are....barely adequate.

We could have done the whole job conventional with a lot less uncertainty, in the same - or less time, considering changing horses in the middle of the stream during the project. I suppose we will spend another hour looking at the data tomorrow to decide if it's worth the risk of using.

BUT... On the lighter side... too danged funny.... WHILE I was downloading the very long L1/L2 2 second epoch base unit files, I decided to go dig out my very first shotgun given to me by one of my grandfathers. A buddie and I decided we would try skeet shooting at the club range with our oldest .410 guns. Anyhow, I had a GPS unit downloading, and was walking by the office door with the old gun in my hand - headed to the drafting table (actually now the gun cleaning table) when all of a sudden there was a knock at the door - at 8:50 p.m. Well, I turned and hit the porch light, opened the door, and there was a young "Amazon Girl" (lots bigger than me) standing there holding a bottle of "Spot Remover". This was at 8:50 P.M., night time in the country. I forgot I was holding a shotgun in my right hand, and she didn't notice. She was holding her "Spot Remover" in her right hand and when I opened the door she held out her left hand to introduce herself as "Amanda". She was a big ole girl, too. As I said, I forgot about the shotgun in my right hand (it had at least 25 years worth of congealed gunk in it) and actually did the left hand "shake" with her. Then told her "You're at the WRONG place". She still tried to give me her line about the "Spot Remover" (at 8:50 p.m. - in the freakin country), and again I said the same words "You're at the WRONG place". Then she looked down and saw the old shotgun, mumbled something about "thank you anyway", turned and ran to a waiting vehicle saying something about "he answers the door with a gun".... I didn't even get a chance to see what kind of vehicle it was. Funny stuff happens.

Life is good.

jd

Hopefully your sessions will still process OK. If you are confident with your mission planning and have open sky but still losing lock, something is wrong. I have observed this infrequently and recommend shutting the unit down and resetting the antenna connections before restarting and initializing a new session. I do sometimes wonder about solar flares and of course we are constantly pushing our projects beyond locations with perfectly open sky.

You may want to look at the signal quality plots for the extra satellite data collected by your base units for some clues to what was going on.

The number of satellites that are shown collecting data on the bar screen of the PM2 does not always correspond with the number of satellites on the main screen. Sometimes the main screen also indicates something different than what you see at post processing time.

You can get good S&G data with six satellites but if the PDOPs are jumping around over 4 it becomes questionable.

I’ve observed a number of situations where one base unit provides fixed solutions while another does not. I believe it mostly has to do with the distance from the base to the rover. It’s hard to get a perfect location for every base and the wavering of tree limbs and sometimes antennas in the wind might also be a factor.

We recently did a big job that extended over ½ mile with three people on PM2 rovers and three base units. Placed base units on both ends plus a roof top reference station less than 5 miles away. The post processing can get confusing and needs to be broken up into different sessions. In my experience if one base provides a fixed solution for the rover but another does not the software automatically selects the best solution for the export file.

Are you sure she didn't say "sock removal"?? Have you hugged your riding mower tonight??

;)

Dangerous Dave

an'up from the ground came some bubblin' crude"

(using)

"sock remover"

(wearing)

"texas tee"

Try to get some work done tomorrow. They will turn off 04 on Tuesday, day 277.

J.D. What was the yellow brick looking at, or was it just thinking optimistically?

Paul in PA

I downloaded a "today" almanac from Thales today(this morning).

The almanac indicated 25 working this morning, but of course, 25 didn't show up on my GPS.

Can anyone tell me if some sources of Almanacs do not include an up-to-date recording, cause I don't know why 25 was in the almanac.

Depends where Thales got the almanac. 25 was turned on at 19:05 zulu, 3:05PM EDT. It was not a planned outage, so all the other satellites thought 25 was on and OK.

I just downloaded alm05.272 from the ftp site and it tells me 25 was not on.
If you where working after 3PM you might have seen 25 for about 2 hours.

Yesterday I based the number of available satellites on a 15° mask. It you used a 10° mask more were available. I don't think it is good to plan your livelyhood on 10-15° satellites. Yes use them if they are there but don't count on them, as they are the most easily obscured.

Paul in PA

25 was a zenith sat(paired with either 01 or 11 I think) from 9am to about 1pm today according to my day 271 almanac. I won't miss 04 at all for now and I don't know how much good 25 will do.

By the way, I got the almanac at about 9 am this morning.

25 is an almost all day satellite, 8:15AM-3:00PM EDT, so it can really be missed if it is unhealthy. It was turned off, or turned itself off at 12:35AM EDT yesterday, 271. The Almanac was already in effect for the day.

While the alm05.271 might have said it was going to be there, the Coast Guard emailed me at 1:30AM on day 271 and told me it was not. NANUs trump almanacs every day of the week.

Paul in PA

25 was critical for me, I would've believed it was there and figured it into my session decisions.

Where's the BEST place to get almanacs from?

"Where's the BEST place to get almanacs from?"


The best place to get almanacs from is directly from the satellites. Like LPL said, the NANUs either enhance or totally supercede the almanac files.

I always assumed that ALL almanacs came directly from the sats.

Either I set up my PM2 and get an almanac and download it to my computer, or Thales-Ashtech personnel did the same thing with a different GPS unit. Since, each day, the almanac has an updated suffix, I asumed that this was done daily.

I also assumed that outages were indicated in the "updated", almanacs and that reports from the feds(the reports I "used" to get, indicating the health of sats was redundant if a person had a new almanac, to the date of that almanac.

Evidently, all this is wrong and up-dated almanacs don't always indicate the "whole" story(sat outages, etc), at the time the almanac is collected.

Almanacs are created on the ground then sent to all the satellites. You can get them from ground sources also, JPL, etc. The almanac is the predicted orbits. It gives the values for all the different parts of each satellites orbital equations. As long as satellites are not repositioned by firing of thrusters an almanac can predict the positions long after its actual date. The predicted almanacs cannot predict the satellite health. The daily almanac includes the satellite health at the time it was created. Yesterdays almanac .272 would not give me good information to plan today's GPS work, Satellite 25 is flagged unhealthy. Having gotten a NANU saying that is was now healthy I would have to turn it on in my planning software. The almanac includes all satellite orbits, even 31 which is essentially turned off. I would be better off to get a new almanac.

The satellites then send it as extra data on top of the standard GPS signal. Not all the satellites get the update at the same time. The GPS receiver figures out which is the newest almanac and does not listen and save the old. That is just one of the many little understood pieces of what goes into making a GPS receiver. Even a cheap simple Map 330 can figure out which is the newer almanac. I have downloaded almanacs from Map 330s and they have the same error as the ProMarks in missing certain satellites in the almanac.

John, go to the navcenter site and sign up for both sets of messages. They are slightly different from before. When mine stopped coming I went and signed up for the new? service. I have gotten up to 4 messages a day.

Satellite 25 was where it was supposed to be and it was transmitting a signal. The signal said "I've got a bug, so I am not coming in to work today." or something slightly more official.

PM2s are not a good source for almanacs.

Paul in PA

I did a 1 hour session this morning 10-11 CDT. The Solutions indiacted that I had 8 SV's and a 1.9 PDOP average for the session.

Was transfering an elevation 5 miles.
Excellent results.