Known position of base

I am new to all this and trying to understand it all and had a couple questions.
We are going to do some drone 3d mapping and will be placing some GCPs.
From my understanding we use a base and a rover to get the locations for the GCPs. But for accurate real world GPS we need to put the base over a (known position).

Question 1 : Can the reach base figure out it’s own “known true location” ? From my reading I thinking we would we just leave it there 4+ hours and record raw data and use PPP to figure out the true location? Then we could manually enter it into the base and start using it with rovers? Or would we have to hire a survey guy with a l2 device to figure out a “known location” ?

Question 2 : If I wanted to permanently make a “know location”. for example a small concrete 1ftx1ft square with X on it. And wrote down the “known location” would I need to subtract the distance from the concrete marker to the antenna used to obtain the “known location”. Like if the reach device got the known location wouldn’t it be off by the height of where ever the reach antenna was for the next person using the concrete maker?

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PPP would give you ~30cm accuracy. Dont you have ntrip serivce you can log on to? or a known position somewhere?

The coordinate for the concrete mark/bolt/pin should be true. Like on top of the measured area. Not 2m above or with any offset.

I live in tx and the rtk Network here is owned by the Department of Transportation and they don’t let anyone use it. All of the other services seem to want a lot of money per month I’m trying to do this for cheap as possible. So using PPP at the base station wouldn’t get me what’s considered a true location? The place I’m doing at at is in the middle of nowhere. I wouldn’t even know where to look for known locations.

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For the known location are you guys talking about like there should be some sort of marker on the property that some a surveyor did a long time ago or some sort of known location along the roads set up by local government or cities somewhere close by? Sorry I’m new to all this and still trying to figure it all out.

We have a similar situation here. The price for using VRS or official bases is ridiculous high.
But, around our country we ha fixed points with known coordinates we can use, their accuracy vary from sub cm to many cm. You may have similar. They could be monuments, poles, buildings, spots or marks on the ground etc etc.
Otherwise, if you are located fairy close to you mission site, getting a surveyor to survey a point for you to use. It could be a home made pole of concret and so on.
Or if your site is to far off, having a surveyor to mark on spot for you to use.
But, i would first check if you have a grid with known fixed monuments around your state. Texas that is?

So if I found a known local spot around me. Such as a monument. Would that mean I would leave my base station sitting on top of it? Would I have to leave a second person so they are guarding it? So from what I gather a professional surveyor would be able to mark a known location on my property better than I could with the reach device?

Yes.

You could, like in the city. Or if you trust this monuments with its coodinates, create you own in an area a bit more secure.

Probably. They have access to services and the knowledg to survey down to few mm.

What about making his own point from know point …

I believe the Texas Department of Transportation Lets you download files for PPK use just not live rtk. Could I find the true location using PPK and a reach device and it would be more accurate than PPP?

Yes you will get better results but depending on distance between reach and TX base.
Better is to traingulate your position with multiple TX base (3 or 6) and to make average position for all 3-6 ppk corrections.

Network is dense IMO as we could see in this pdf : https://www.gps.gov/cgsic/states/2012/austin/fuegner.pdf

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Ok I think I might have figured out how to get true “known position” of a reach base using another base somewhere else. Without going to a monument or anything. Can anyone tell me if this sounds right?

Setup the reach base somewhere and put it into single mode. Log raw data for 1 hour. Is single mode the right mode or should it be static or kinematic?

Even though they don’t let you use real time RTK network the texas dept of transportation has a FTP website with all the base stations it operates. Using maps I found the closest one to me and went to it’s folder and downloaded the latest RINEX file.

http://ftp.dot.state.tx.us/pub/txdot-info/isd/gps/RINEX/txac/
The part that I didn’t understand was the files inside the ZIP are not OBS extension. They are 18g 18o and 18n extensions.

So I put the 18o in the RTKconv and it made a OBS file.

Then I used RTKpost and put the Raw obs file from my base and the raw OBS file from the texas dept of transportation base and processed them.

After that I put the plot file into RTKplot and saw a bunch of green dots. I changed the drop down to “position” and saw a ORI coordinates. Is the ORI my true location?

Thanks!

You could also try submitting your raw-data (converted to Rinex) to this service, and see what precision comes back: https://webapp.geod.nrcan.gc.ca/geod/tools-outils/ppp.php

I, for one, would be very curious to hear the result.

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