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Creating my own control point w. no base station in range


(Derrick) #1

My company is looking at getting two Reach RS2s so we can establish our own GCPs. Most cases we will just need high relative accuracy to check for scaling issues with photogrammetry projects.

I’m wondering if anyone can share some workflow ideas or correct me if I’m wrong on any ideas I have. I want to know workflow without using RTK correction networks.

Case 1: set GCPs for scaling checks. Set base RS2 up with no known point, use rover RS2 to collect GCPs. Simple, no processing, I can check relative accuracy of my project this way.

Case 2: set base on known point, rover will data collect georeferenced GCPs. No post processing.

Case 3: I have no known point and want to set my own control. My understanding is that it’s best to leave base logging for an hour minimum and then download RINEX data from the closest source. (Which is available if I’m in my normal region). My question here is can I data collect GCPs with the rover as the base is logging? And how do I apply PPK corrections to these observations?

Case 4: I am >100km from a known active control point but I need to georeference my GCPs. How do I do this?

Thanks


(Michael Lambert) #2

With the new RS2 you should be able to let it collect a point for about 10 minutes and then do RTK for your GCP’s. This would not work well with the previous L1 only receivers. There should be no need to process. Just set a hub or some type of monument in the ground and note the coordinate that the base collects. You can then return to that point in the future and manually enter the same coordinate so that all of your surveys are relative. The only other scenario beyond that would be the localization method that you can learn about in many threads on the forum. Feel free to PM me and we can get you up to speed in about 15 minutes.


#3

:+1:

:+1:

:+1:

You would submit your base log file (preferably 2 hours or more) to a (free) PPP service, such as the one provided by the National Research Council of Canada (NRCAN). There are many references to NRCAN PPP processing here on the forum.


(Michael Lambert) #4

Case 4:
If you have a base and rover why do you need any additional information?


#5

@chascoadmin Only because of his georeference requirement:

I mean with RS2, you could still try RTK to the >100km active control point, but “your mileage may vary” :slight_smile:


(Michael Lambert) #6

What is the requirement beyond getting a fixed (control) point to return to? I am missing something. I don’t see where there is a specific requirement to georeference to anything other than the base station? The GCP’s are all relative to that and each other.


#7

You have a good point Michael. It seems there are a lot of people thinking they need absolute coordinates, when really they just need site-relative data and a control point(s) to work from, just like you have mentioned several times.

But, if the requirement is for the data to be geo-referenced and a 2cm relative accuracy site with a 2.5 meter accuracy control point is not good enough for a remote & out-of-the-service-area site, then PPP or long-distance RTK/PPK may be required to meet the requirements.

Do you agree?


(Michael Lambert) #8

I think so. When I think geo-referenced I just think of a GPS derived coordinate. Not necessarily globally accurate to every other control point on the planet. My understanding of what they were looking for is just the ability to set GCP’s so that the survey was horizontally accurate. The thing is though that with a drone survey because of the photogrammetry process they will already be horizontally accurate. GCP’s only slightly increase the relative accuracy horizontally, but greatly affect the vertical and global accuracy.


#9

Yep, I get it. But I think the masses believe that because you have 6 or 7 decimal places behind your LLH or 3 decimal places behind your UTM, that it means it represents that accuracy relative to every other point in the world - (especially to Goggle Maps :wink: - but don’t let me get you started on that)


(Christian Grüner) #10

What? You can’t do that in Google Maps? Mind blown! :smiley:

On a serious note, and as a different option, in my country, there is a State-maintained plugin for QGIS which delivers a 20 ish cm/px map aligned to ETRS89 (in UTM) for the entire country. I would guess that other countries would have somewhat the same?


(Michael Lambert) #11

Fresh off another post about differences between GIS Data Collection and Surveying, I put the discussion about Drone Mapping and Surveying in the same line of thinking. Drone mappers shouldn’t use the term or represent themselves as surveyors and they (we) are not Google Earth in the fact that we need to map globally and stitch all of our maps together so that they all align perfectly as defined by GNSS coordinate systems. These projects are more standalone and for the purposes of providing information about the subject. That said, a base/rover scenario creates a “georeferenced” network that the subject is then relative to. Wanting to dimensionally and accurately capture a map of a subject to me is different than trying to tie to all the adjacent plots like a true surveyor would do. Just different use-cases and I might have misunderstood the OP’s intent.


(Christian Grüner) #12

A classic example of the more you know, the more you realize that you also don’t know.
If you just go about it with the “ahhh, it can’t be that hard” mantra, you often find yourself failing miserably, or, if you succeed, not knowing why you succeeded, and thus it will be just as much trial-and-error next time.