I had a couple of topos to do on Friday, along with trying to retrace 1950's era shot points with a client, and my base battery cord (one thing I don't carry a spare for) was not working, so I was left with either trying to repair the cable on site, making the 3hour drive back and forth to the office or using PPK continuous topo and hoping it would connect to the nearest Cors point 35 miles to the west and post process using it.
My client made up my mind as I could see him driving to me from the south so I decided to try the PPK topo mode, it had worked before but that was using TSO and TGO, hadn't tried it yet using TBC.
The day went well, a little frustrating always trying to keep the rover locked while driving through steep ravines and hills, but not bad, got back Monday and couldn't get TBC to process to the CORS data. Going through the help menu wasn't solving my problem, a desperate call to the vender didn't help so I decided to scrub the file and try again.
FACEPALM, I downloaded the first Cors file with the wrong sign for hours from Greenwich, once the correct time was imputed TBC took over the data, processed it and all was well. My check points were dead on (less than .10') the topo shots were about 12 acres of additional topo for two sites about an hour of work, but tough to redo when you need to drive 3 hours to get there. The shot point retracement would take about 3 hours by themselves so....., WHEW!!!
Cable is fixed now, and I think I need to add another to my spare cable collection.
I have only tried PPK once before and it failed because of a problem with the CORS but I would like to try it again. I have limited experience with RTK as I mostly do static campaigns.
Can I ask how many CORS stations did you use, was it one or multiple. What are the baseline length limits of a single CORS for static/PPK/RTK?
I use older equipment and have a base radio/rover setup. PPK works only for locations, if you are staking out you will need to move a radio and get real time connection, but for Friday I didn't need that. I wasn't locating section corners and I needed to collect hundreds of points so static (or fast static) wouldn't work either.
My only option was PPK and a Cors tie. So I started sessions in PPK continuous topo and 5 second point locations. Using 5 second timing means that when you download Cors you have to download it at 5 second data capture or 1 second data capture rates. Either will work but I do 5 because it keeps the file smaller and there is no real advantage to the 1 second rate if the rover is at 5.
Then import the Cors file (make sure you use the datasheet or the newest coordinate-really shouldn't matter for this), then the dc file holding your PPK sessions, and your software will process all the points moving them to the "correct" positions.
I have been using this method since 97, started renting a unit to the county to locate centerline of all the county roads. The engineer mounted a receiver on his SUV, drove each road and tied it to our base on the roof of the office. Even 70 miles away the data was very good, these are one second locations timed by the rover and base and they are very accurate. The important thing is to have the PPK session be long and "clean". Don't lose lock very often!!!
Friday the Cors station was close-30 miles on the west end and 35 miles on the east end so I knew it would work if I could figure out how TBS handles it. My check points were in continuous topo and were less than a .1', this is with a single timed one second shot. I wanted to see how it would check, and was surprised just how tight it is. I don't recommend doing it for something really important, but this was just adding data to existing dirt topos and since I slopped over the old topos I had checks everwhere and it was all good;-)
I did not tie to other cors, the next nearest one is probably almost 100 miles, and PPK continuous topo is set-up for only one tie to a base.
TBC*
Did you consider setting your base up on one of your known points and collecting data and using it for your ppk post processing?
That's how I usually do it, but alas the power cord was defective so the base was not going to power up, I could have probably jury rigged something to get the base going, but this was quicker. Had I needed RTK I would have sat down with the chord and my knife and tried some field surgery on it;-)
As it happens I had to do some PPK last week, when the radio signal dropped out on the RTK job I was working on. I've learnt always to set my base station to log data when I'm doing RTK, just in case - set it to log 1 second, otherwise it involves long waits on each PPK point. I have the PPK set to take 4 readings at 1 second intervals for each point.
The data processed in TBC and agreed well with common points where the RTK signal had cut back in briefly.
Having read this posting, out of interest I've now downloaded the UK equivalent of CORS (OS Active) for the two nearest atations and processed my PPK data against those references.
Using a single reference only gives the following results:
Reference station 15km away to the south : the agreement with my original coordinates was standard deviations of x=8mm, y=7mm, ht=17mm
Reference station 45km away to the east : the agreement with my original coordinates was standard deviations of x=7mm, y=12mm, ht=20mm
For many purposes this would be quite satisfactory. The biggest risk is finding that the reference network has suffered an outage whilst you were surveying - not common but it does happen and somebody is no doubt surveying when it does and cursing when they eventually find out.
As it happens I had to do some PPK last week, when the radio signal dropped out on the RTK job I was working on. I've learnt always to set my base station to log data when I'm doing RTK, just in case - set it to log 1 second, otherwise it involves long waits on each PPK point. I have the PPK set to take 4 readings at 1 second intervals for each point.
Honestly, I don't even have an RTK survey style in my data collector anymore except for the factory default one that I've never use. Every time I set up my base I use the RTK/Infill style, which is just what you do. The only difference is I set mine at 5 second logging, I had trouble with the 1 second timing and quit using it, but I don't remember what that problem was, lol. Guess it was too long ago.