Waiting time to submit to DPOS

Aaron S

Active Member
What is the ideal time to wait to hit the "send to DPOS" button on the LS? After a certain time period, the improvement is extremely minimal, but if it's too soon I'm sure that's not very good.

Does it make a difference whether or not you're using a known base point, or an autonomous point then reverse-shifting it?
 

Adam

Well-Known Member
5PLS
What is the ideal time to wait to hit the "send to DPOS" button on the LS? After a certain time period, the improvement is extremely minimal, but if it's too soon I'm sure that's not very good.

Does it make a difference whether or not you're using a known base point, or an autonomous point then reverse-shifting it?
I usually run dpos that evening. Sometimes the next morning. The results are pretty similar. If you try it to early it will say waiting on cors or use cors that are available but too far away to give good results. In that case wait and try later.

It doesn't matter.
 

Steve Douty

Well-Known Member
The following is an answer from someone who is just guessing. Based on my limited, uneducated experience I have found the following:

1) I can submit data to DPOS one to two hours after I have gathered the data and generally get a CORS solution. The solution is however based on whatever CORS stations have been downloaded at the time. This means the solution may be based on a minimum number of CORS stations, a long way away from my project and not the best ephemeris. I have found that the solutions are sometimes very good, and sometimes may disagree with later solutions (using the same data) on an order of magnitude of one foot.

2) Shortly after "GPS Midnight" (1 hour) I get solutions that compare very well to more careful observations.

3) If I wait several hours after GPS Midnight or a few days I find the solution uses more and closer CORS stations and maybe better ephemeris. I would love to know how to determine which ephemeris are being used.

4) I believe that using a known base point, and holding the known value can be processed at any time. What DPOS does for us is allow PPK processing and maybe CORS comparisons depending on length of occupation and everything discussed above. I often will go to DPOS settings and chose the "Base-Rover Processing only" option. This allows me to ignore any CORS static.

Now is the time for those who know what they are talking about to tear into all of the above.
 

Steve Douty

Well-Known Member
Where can I find a summary of the different ephemeris and there timing? Also does the statement by Razumovsky mean we never have access to "the good stuff" through DPOS?
 

Adam

Well-Known Member
5PLS
From what I remember he said the broadcast deals just as good solutions as the others. I may be remembering wrong and there maybe other reasons.
 

Steve Douty

Well-Known Member
Thanks Alexey,

I can't think of a time when my procedure, equipment adjustment, center on point, measure HI and other factors were better than 0.1mm.
 

Aaron S

Active Member
Thanks everyone for the replies. Here's the basic situation I'm running to on the project they have me on:

I have corners to shoot that are very spread out, several miles in between. My preference is to use the LS as internet rover on the state's RTN to get RTK solutions.

More often, the canopy prevents this, so sometimes I can get a good result from DPOS using a 30-minute raw data file from the LS that I collected while waiting to get a fix (but this is kind of risky).

Usually, I have to set up a local base to shoot one point. Let's assume I can set up the base within a mile or two of the point I need in open sky, and can use the RTN to set an RTK point for the base to set on (establish a known point). What would be the best method to get a good position on the point in canopy, keeping in mind that radio link may not be available?
 

Nate The Surveyor

Well-Known Member
Just an idea. If you can get that base up 30' into the good, it's just way better. Don't fret about repeatability, of the base gps. Set a nail to reverse shift in the base coords. (M-local) I've done this quite successfully.
Nate
 

Aaron S

Active Member
I'd lean toward post processing the base rover vector with dpos over cors processing for the point in canopy. If I'm relying on ppk only definitely shoot it twice.
What I've been doing when setting a local base is shooting the point 3 times, 10 minutes each time, rotating the pole 120 degrees between shots. Sometimes this gets good results, sometimes the 3 points don't agree. I'm trying to find a balance between getting good numbers, but not spending hours on a point.

In general, is a PPK result better than an RTK result?
 

Aaron S

Active Member
Just an idea. If you can get that base up 30' into the good, it's just way better. Don't fret about repeatability, of the base gps. Set a nail to reverse shift in the base coords. (M-local) I've done this quite successfully.
Nate
I can get a good base location set, it's just the point that I'm shooting off that base is where I have canopy problems. And isn't repeatability what it's all about? Maybe I'm not understanding here.
 

Duane Frymire

Active Member
I can get a good base location set, it's just the point that I'm shooting off that base is where I have canopy problems. And isn't repeatability what it's all about? Maybe I'm not understanding here.
I think Nate is referring to when the base location isn't that great. Generally, your sideshot under canopy is going to be better the closer the base is to it. So, it might be worth moving the base closer than a couple miles and sending it up in the air if you have to in order to get a good base solution closer to the rtk/ppk shot. Sometimes a couple miles is nothing, but sometimes it can have an affect in my experience. Depends on the troposphere conditions. The textbooks seem to disagree with me, but my less than scientific observations are that it troposphere is playing a major role in my ability to get good positions. We do have some weird weather here on east side of tug hill plateau on east side of great lakes.
 

Aaron S

Active Member
So is PPK pretty much the same thing as RTK? If I shoot a point off a local base (say for example, 10 minutes) I'll get two coordinates for that point, RTK and PPK. If they agree with each other within 0.03' or so, what are the odds that they are both wrong? Are the two methods a truly independent check?
 

Matthew D. Sibole

Well-Known Member
5PLS
I have had them both be wrong. That is why I recommend shooting the point 3 times. I want to prove it is repeatable and build in redundancy.
 
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